Biological Exposure Indices (BEI®) Introduction

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Policy Statement on the Uses of TLVs® and BEIs®

The Threshold Limit Values (TLVs®) and Biological Exposure Indices (BEIs®) are developed as guidelines to assist in the control of health hazards. These recommendations or guidelines are intended for use in the practice of industrial hygiene, to be interpreted and applied only by a person trained in this discipline. They are not developed for use as legal standards and ACGIH® does not advocate their use as such. However, it is recognized that in certain circumstances individuals or organizations may wish to make use of these recommendations or guidelines as a supplement to their occupational safety and health program. ACGIH® will not oppose their use in this manner, if the use of TLVs® and BEIs® in these instances will contribute to the overall improvement in worker protection. However, the user must recognize the constraints and limitations subject to their proper use and bear the responsibility for such use.

The Introductions to the TLV®/BEI® Book and the TLV®/BEI® Documentation provide the philosophical and practical bases for the uses and limitations of the TLVs® and BEIs®. To extend those uses of the TLVs® and BEIs® to include other applications, such as use without the judgment of an industrial hygienist, application to a different population, development of new exposure/recovery time models, or new effect endpoints, stretches the reliability and even viability of the database for the TLV® or BEI® as evidenced by the individual Documentation.

It is not appropriate for individuals or organizations to impose on the TLVs® or the BEIs® their concepts of what the TLVs® or BEIs® should be or how they should be applied or to transfer regulatory standards requirements to the TLVs® or BEIs®.

Approved by the ACGIH® Board of Directors on March 1, 1988.

Special Note to User

These values are intended for use in the practice of industrial hygiene as guidelines or recommendations to assist in the control of potential workplace health hazards and for no other use. These values are not fine lines between safe and dangerous concentrations and should not be used by anyone untrained in the discipline of industrial hygiene. It is imperative that the user of these values read the Introduction to each section of the TLV®/BEI® Book and be familiar with the Documentation of the TLVs® and BEIs® before applying the recommendations. ACGIH® disclaims liability with respect to the use of the TLVs® and BEIs®.

Statement of Position Regarding the TLVs® and BEIs®

The American Conference of Governmental Industrial Hygienists (ACGIH®) is a private not-for-profit, nongovernmental corporation whose members are industrial hygienists or other occupational health and safety professionals dedicated to promoting health and safety within the workplace. ACGIH® is a scientific association. ACGIH® is not a standards setting body. As a scientific organization, it has established committees that review the existing published, peer-reviewed scientific literature. ACGIH® publishes guidelines known as Threshold Limit Values (TLVs®) and Biological Exposure Indices (BEIs®) for use by industrial hygienists in making decisions regarding safe levels of exposure to various chemical and physical agents found in the workplace. In using these guidelines, industrial hygienists are cautioned that the TLVs® and BEIs® are only one of multiple factors to be considered in evaluating specific workplace situations and conditions.

Each year ACGIH® publishes its TLVs® and BEIs® in a book. In the introduction to the book, ACGIH® states that the TLVs® and BEIs® are guidelines to be used by professionals trained in the practice of industrial hygiene. The TLVs® and BEIs® are not designed to be used as standards. Nevertheless, ACGIH® is aware that in certain instances the TLVs® and the BEIs® are used as standards by national, state, or local governments.

Governmental bodies establish public health standards based on statutory and legal frameworks that include definitions and criteria concerning the approach to be used in assessing and managing risk. In most instances, governmental bodies that set workplace health and safety standards are required to evaluate health effects, economic and technical feasibility, and the availability of acceptable methods to determine compliance.

ACGIH® TLVs® and BEIs® are not consensus standards. Voluntary consensus standards are developed or adopted by voluntary consensus standards bodies. The consensus standards process involves canvassing the opinions, views and positions of all interested parties and then developing a consensus position that is acceptable to these parties. While the process used to develop a TLV® or BEI® includes public notice and requests for all available and relevant scientific data, the TLV® or BEI® does not represent a consensus position that addresses all issues raised by all interested parties (e.g., issues of technical or economic feasibility). The TLVs® and BEIs® represent a scientific opinion based on a review of existing peer-reviewed scientific literature by committees of experts in public health and related sciences.

ACGIH® TLVs® and BEIs® are health-based values. ACGIH® TLVs® and BEIs® are established by committees that review existing published and peer-reviewed literature in various scientific disciplines (e.g., industrial hygiene, toxicology, occupational medicine, and epidemiology). Based on the available information, ACGIH® formulates a conclusion on the level of exposure that the typical worker can experience without adverse health effects. The TLVs® and BEIs® represent conditions under which ACGIH® believes that nearly all workers may be repeatedly exposed without adverse health effects. They are not fine lines between safe and dangerous exposures, nor are they a relative index of toxicology. The TLVs® and BEIs® are not quantitative estimates of risk at different exposure levels or by different routes of exposure.

Since ACGIH® TLVs® and BEIs® are based solely on health factors, there is no consideration given to economic or technical feasibility. Regulatory agencies should not assume that it is economically or technically feasible for an industry or employer to meet TLVs® or BEIs®. Similarly, although there are usually valid methods to measure workplace exposures at TLVs® and BEIs®, there can be instances where such reliable test methods have not yet been validated. Obviously, such a situation can create major enforcement difficulties if a TLV® or BEI® was adopted as a standard.

ACGIH® does not believe that TLVs® and BEIs® should be adopted as standards without full compliance with applicable regulatory procedures including an analysis of other factors necessary to make appropriate risk management decisions. However, ACGIH® does believe that regulatory bodies should consider TLVs® or BEIs® as valuable input into the risk characterization process (hazard identification, dose-response relationships, and exposure assessment). Regulatory bodies should view TLVs® and BEIs® as an expression of scientific opinion.

ACGIH® is proud of the scientists and the many members who volunteer their time to work on the TLV® and BEI® Committees. These experts develop written Documentation that include an expression of scientific opinion and a description of the basis, rationale, and limitations of the conclusions reached by ACGIH®. The Documentation provides a comprehensive list and analysis of all the major published peer-reviewed studies that ACGIH® relied upon in formulating its scientific opinion. Regulatory agencies dealing with hazards addressed by a TLV® or BEI® should obtain a copy of the full written Documentation for the TLV® or BEI®. Any use of a TLV® or BEI® in a regulatory context should include a careful evaluation of the information in the written Documentation and consideration of all other factors as required by the statutes which govern the regulatory process of the governmental body involved.

  • ACGIH® is a not-for-profit scientific association.
  • ACGIH® proposes guidelines known as TLVs® and BEIs® for use by industrial hygienists in making decisions regarding safe levels of exposure to various hazards found in the workplace.
  • ACGIH® is not a standards setting body.
  • Regulatory bodies should view TLVs® and BEIs® as an expression of scientific opinion.
  • TLVs® and BEIs® are not consensus standards.
  • ACGIH® TLVs® and BEIs® are based solely on health factors; there is no consideration given to economic or technical feasibility. Regulatory agencies should not assume that it is economically or technically feasible to meet established TLVs® or BEIs®.
  • ACGIH® believes that TLVs® and BEIs® should NOT be adopted as standards without an analysis of other factors necessary to make appropriate risk management decisions.
  • TLVs® and BEIs® can provide valuable input into the risk characterization process. Regulatory agencies dealing with hazards addressed by a TLV® or BEI® should review the full written Documentation for the numerical TLV® or BEI®.

ACGIH® is publishing this Statement in order to assist ACGIH® members, government regulators, and industry groups in understanding the basis and limitations of the TLVs® and BEIs® when used in a regulatory context. This Statement was adopted by the ACGIH® Board of Directors on March 1, 2002.

TLV®/BEI® Development Process: An Overview Provided below is an overview of the ACGIH® TLV®/BEI® Development Process. Please also refer to the Process Flowchart (Figure 1).

  1. Under Study: When a substance or agent is selected for the development or revision of a TLV® or BEI®, the appropriate committee places it on its Under Study list. Each committee determines its own selection of chemical substances or physical agents for its Under Study list. A variety of factors is used in this selection process, including prevalence, use, number of workers exposed, availability of scientific data, existence/absence of a TLV® or BEI®, age of TLV® or BEI®, input from the public, etc. The public may offer input to any TLV® or BEI® Committee by e-mail to

    The Under Study lists serve as notification and invitation to interested parties to submit substantive data and comments to assist the committees in their deliberations. Each committee considers only those comments and data that address issues of health and exposure, but not economic or technical feasibility. Comments must be accompanied by copies of substantiating data, preferably in the form of peer-reviewed literature. Should the data be from unpublished studies, ACGIH® requires written authorization from the owner of the studies granting ACGIH® permission to (1) use, (2) cite within the Documentation, and (3) upon request from a third party, release the information. All three permissions must be stated/covered in the written authorization. (See endnote for a sample permission statement.) Electronic submission of all information to the ACGIH® Science Group at is preferred and greatly increases the ease and efficiency with which the committee can consider the comments or data.

    The Under Study list is published each year by February 1 on the ACGIH® website (, in the Annual Reports of the Committees on TLVs® and BEIs®, and later in the annual TLVs® and BEIs® book. In addition, the Under Study list is updated by July 31 into a two-tier list.  

    • Tier 1 entries indicates which chemical substances and physical agents may move forward as an NIC or NIE in the upcoming year, based on their status in the development process.

    • Tier 2 consists of those chemical substances and physical agents that will not move forward, but will either remain on, or be removed from, the Under Study list for the next year.

    This updated list will remain in two-tiers for the balance of the year. All updates to the Under Study lists and publication of the two-tier lists are posted on the ACGIH® website (  

  2. Draft Documentation: One or more members of the appropriate committee are assigned the task of collecting information and data from the scientific literature, reviewing results of unpublished studies submitted for review, and developing a draft TLV® or BEI® Documentation. The draft Documentation is a critical evaluation of the scientific literature relevant to recommending a TLV® or BEI®; however, it is not an exhaustive critical review of all studies but only those pertinent to identifying the critical effect and setting the TLV®. Particular emphasis is given to papers that address minimal or no adverse health effect levels in exposed animals or workers that deal with the reversibility of such effects, or in the case of a BEI®, that assess chemical uptake and provide applicable determinant(s) as an index of uptake. Human data, when available, are given special emphasis. This draft Documentation, with its proposed TLV® or BEI®, is then reviewed and critiqued by additional committee members, and eventually by the full committee. This often results in several revisions to the draft Documentation before the full committee accepts the proposed draft TLV® or BEI® and draft Documentation. The draft Documentation is not available to the public during this stage of the development process and is not released until it is at the Notice of Intended Changes (NIC) stage. Authorship of the Documentation is not disclosed.

  3. Notice of Intended Changes (NIC):
    [Notice of Intent to Establish (NIE): The Physical Agents section of the TLVs® and BEIs® book also uses the term Notice of Intent to Establish (NIE) in addition to NIC. An NIE follows the same development process as an NIC. For purposes of this process overview, only the term NIC is used.]

    When the full committee accepts the draft Documentation and its proposed TLV® or BEI®, the Documentation and proposed values are then recommended to the ACGIH® Board of Directors for ratification as an NIC. If ratified, each proposed TLV® or BEI® is published as an NIC in the Annual Reports of the Committees on TLVs® and BEIs®, which is published in the ACGIH® member newsletter, Today! Online and is also available online for purchase at At the same time, the draft Documentation is made available through ACGIH® Customer Service or online at All information contained in the Annual Reports of the Committees on TLVs® and BEIs® is integrated into the annual TLVs® and BEIs® book, which is usually available to the general public in February or March of each year. Following the NIC ratification by the ACGIH® Board of Directors, interested parties, including ACGIH® members, are invited to provide data and substantive comments, preferably in the form of peer-reviewed literature, on the proposed TLVs® or BEIs® contained in the NIC. Should the data be from unpublished studies, ACGIH® requires written authorization from the owner of the studies granting ACGIH®permission to (1) use, (2) cite within the Documentation, and (3) upon request from a third party,release the information. All three permissions must be stated/covered in the written authorization. (See endnote for a sample permission statement.) The most effective and helpful comments are those that address specific points within the draft Documentation. Changes or updates are made to the draft Documentation as necessary. If the committee finds or receives substantive data that change its scientific opinion regarding TLV® or BEI® values or notations, the committee may revise the proposal(s) and recommend to the ACGIH® Board of Directors that it be retained on the NIC.

    Important Notice: The comment period for an NIC or NIE draft Documentation and its respective TLV(s)®, notation(s), or BEI(s)®, will be limited to a firm 4-month period, running from February 1 to May 31 of each year. ACGIH® has structured the comment period to ensure all comments are received by ACGIH® in time for full consideration by the appropriate committee before its fall meeting. Because of the time required to properly review, evaluate, and consider comments during the fall meetings, any comments received after the deadline of May 31 will not be considered in that year's committee deliberations regarding the outcome for possible adoption of an NIC or NIE. As general practice, ACGIH® reviews all submissions regarding chemical substances and physical agents on the Under Study list, as well as NICs or NIEs, or currently adopted BEI(s)® or TLV(s)®. All comments received after May 31 will be fully considered in the following year. Draft Documentation will be available for review during the comment period.

    When submitting comments, ACGIH® requires that the submission be limited to 10 pages in length, including an executive summary. The submission may include appendices of citable material not included as part of the 10-page limit. It would be very beneficial to structure comments as follows:

      The above procedure will help ACGIH® to more efficiently and productively review comments.

    1. TLV®/BEI® and Adopted Documentation: If the committee neither finds nor receives any substantive data that change its scientific opinion regarding an NIC TLV® or BEI® (or notation), the committee may then approve its recommendation to the ACGIH® Board of Directors for adoption. Once approved by the committee and subsequently ratified by the Board, the TLV® or BEI® is published as adopted in the Annual Reports of the Committees on TLVs® and BEIs® and in the annual TLVs® and BEIs® book, and the draft TLV® or BEI® Documentation is finalized for formal publication.

    2. Withdraw from Consideration: At any point in the process, the committee may determine not to proceed with the development of a TLV® or BEI® and withdraw it from further consideration. Substances or physical agents that have been withdrawn from consideration may be reconsidered by placement on the Under Study list (step 1 above).

       There are several important points to consider throughout the above process:

      1. The appropriate method for an interested party to contribute to the TLV® and BEI® process is through the submission of literature that is peer-reviewed and public. ACGIH® strongly encourages interested parties to publish their studies, and not to rely on unpublished studies as their input to the TLV® and BEI® process. Also, the best time to submit comments to ACGIH®is in the early stages of the TLV® and BEI® Development Process, preferably while the substance or agent is on the Under Study list.


      2. An additional venue for presentation of new data is an ACGIH®-sponsored symposium or workshop that provides a platform for public discussion and scientific interpretation. ACGIH®encourages input from external parties for suggestions on symposium topics, including suggestions about sponsors, speakers and format. ACGIH® employs several criteria to determine the appropriateness of a symposium. A key criterion is that the symposium must be the most efficient format to present the committee with information that will assist in the scientific judgment used for writing the Documentation and in setting the respective TLVs® or BEIs®. A symposium topic should be suggested while the substance/agent is under study, as symposia require considerable time, commitment, and resources to develop. Symposium topic suggestions submitted while a substance is on the NIC will be considered, but this is usually too late in the decision-making process. A symposium topic will not be favorably considered if its purpose is to provide a forum merely for voicing opinions about existing data. Rather, there must be on-going research, scientific uncertainty about currently available data, or another scientific reason for the symposium. Symposium topic suggestions should be sent to the ACGIH® Science Group (


      3. ACGIH® periodically receives requests from external parties to make a presentation to a committee about specific substances or issues. It is strictly by exception that such requests are granted. While there are various reasons for this position, the underlying fact is that the committee focuses on data that have been peer-reviewed and published and not on data presented in a private forum. A committee may grant a request when the data is significantly new, has received peer review, is the best vehicle for receipt of the information, and is essential to the committee's deliberations. The presentation is not a forum to merely voice opinions about existing data. In order for a committee to evaluate such a request, the external party must submit a request in writing that, at a minimum, addresses the following elements: (a) a detailed description of the presentation; (b) a clear demonstration of why the information is important to the committee's deliberations; and (c) a clear demonstration of why a meeting is the necessary method of delivery. This request must be sent to the ACGIH® Science Group (

        Also, the committee may initiate contact with outside experts (a) to meet with the committee to discuss specific issues or to obtain additional knowledge on the subject, and (b) to provide written input or review of a Documentation. This is only done on an as needed basis, and not as a routine practice.

      4. ACGIH® does not commit to deferring consideration of a new or revised TLV® or BEI® pending the outcome of proposed or ongoing research.


      Important dates to consider throughout each calendar year of the TLV®/BEI® Development Process:

      First Quarter:

      Year Round

      • Public comments are accepted. See Note below.


      • Committees meet.
      Note: It is recommended that comments be submitted as early as practical, and preferably no later than May 31st to allow sufficient time for their proper consideration/review. This is particularly important for an NIC TLV®/BEI®.


      Important Notice: The comment period for an NIC or NIE draft Documentation and its respective TLV(s)®, notation(s), or BEI(s)®, will be limited to a firm 4-month period, running from February 1 to May 31 of each year. (See Important Notice, step 3 above.)

      Third Quarter:

      Fourth Quarter
      : *

      • TLV®/BEI® Committees vote on proposed TLVs®/BEIs® for NIC or final adoption.


      • ACGIH® Board of Directors votes on ratification of TLV®/BEI® Committee recommendations.
      * These actions typically occur early in the fourth quarter, but may occur during other periods of the quarter or year.

      Endnote: Sample permission statement granting ACGIH® authorization to use, cite, and release unpublished studies:


      [Name], [author or sponsor of the study**] grants permission to ACGIH® to use and cite the documents listed below, and to fully disclose them to parties outside of ACGIH® upon request. Permission to disclose the documents includes permission to make copies as needed.

      Example: Joseph D. Doe, PhD, co-author of the study, grants permission to ACGIH®to use and cite the document listed below, and to fully disclose this document to parties outside of ACGIH®. Permission to disclose the document includes permission to make copies as needed.

      "Effects of Quartz Status on Pharmacokinetics of Intratracheally Instilled Cristobalite in Rats. March 21, 2003."
      **This statement must be signed by an individual authorized to give this permission, and should include contact information such as title and address.

      Last Revised April 2012


    Introduction to the Biological Exposure Indices (BEIs®)

    Biological monitoring provides an important means to assess exposure and health risk to workers. It entails measurement of a chemical determinant in the biological media of those exposed and is an indicator of the uptake of a substance. Biological Exposure Indices (BEIs®) are guidance values for evaluating biological monitoring results. BEIs® generally represent the levels of determinants that are most likely to be observed in specimens collected from healthy workers who have been exposed to chemicals to the same extent as workers with inhalation exposure at the Threshold Limit Value–Time Weighted Average (TLV–TWA). However, there are BEIs® for chemicals for which the TLVs® are based on protection against nonsystemic effects (e.g., irritation or respiratory impairment) where biological monitoring is desirable because of the potential for significant absorption via an additional route of entry (usually the skin). There are also BEIs® that better predict health effects than air levels and finally, BEIs® that are based on the levels in the environmentally exposed population. The BEI® generally indicates a concentration below which nearly all workers should not experience adverse health effects. The BEI® determinant can be the chemical itself; one or more metabolites; or a characteristic, reversible biochemical change induced by the chemical. The specimens used for BEIs® are urine, blood, or exhaled air. The BEIs® are not intended for use as a measure of adverse effects or for diagnosis of occupational illness.

    Biological monitoring can assist the occupational health professional (occupational and industrial hygienists, occupational physicians and nurses, etc.) to determine absorption via the skin or gastrointestinal system, in addition to that by inhalation; assess body burden; reconstruct past exposure; detect nonoccupational exposures among workers; test the efficacy of personal protective equipment and engineering controls; and monitor work practices.

    Biological monitoring serves as a complement to exposure assessment by air sampling and medical surveillance. The existence of a BEI® does not indicate a need to conduct biological monitoring. Conducting, designing, and interpreting biological monitoring protocols and the application of the BEI® require professional experience in occupational health and reference to the current edition of the Documentation of the Threshold Limit Values and Biological Exposure Indices (ACGIH®).

    Editor’s note: The approximate year that the current Documentation was last substantially reviewed and, where necessary, updated may be found following the CAS number for each of the adopted entries in the alphabetical listing, e.g., Acetone [67-64-1] (2014). The reader is advised to refer to the “BEI® Chronology” section in each Documentation for a brief history of the BEI® recommendations and notations. 


    It is essential that the user consult the specific BEI® Documentation before designing biological monitoring protocols and interpreting BEIs® for a specific agent. The Documentation for each compound contains the explicit information that is only discussed in general in this Introduction. In addition, each BEI® Documentation now provides a chronology that traces all BEI® recommended actions for the chemical substance in question.

    BEIs® are developed by Committee consensus through an analysis and evaluation process. The detailed scientific criteria and justification for each BEI® can be found in the Documentation of the Threshold Limit Values and Biological Exposure Indices. The principal material evaluated by the BEI® Committee includes peer-reviewed published data taken from the workplace (i.e., field studies), data from controlled exposure studies, and from appropriate toxicokinetic modeling when available. The results of animal research are also considered when relevant. The Documentation provides essential background information and the scientific reasoning used in establishing each BEI®. Information given includes the analytical methods, possible potential for confounding exposures, specimen collection recommendations, limitations, as well as other essential information, specific for each compound and analyte.

    In recommending a BEI®, ACGIH® considers whether published data are of reasonable quality and may also consider unpublished data if a complete copy of the data/report is provided to ACGIH®. However, unpublished data are never used as the primary basis for a BEI®, although it may provide a secondary support. There are numerous instances when analytical techniques are available for the measurement of a biological determinant, but published information is unavailable or inadequate to determine a BEI®. The data needed to establish a BEI® include comprehensive assessment of total exposure and/or health effects. Therefore, occupational health professionals are encouraged to accumulate and report biological monitoring data together with exposure and health data. 

    Relationship of BEIs® to TLVs®

    BEI® determinants are an index of an individual’s uptake of a chemical by all routes. In some cases they correspond to the TLV® as a “safe” level without reported health effects. In other cases they may reflect the highest 5% of levels seen in the general population. In addition, some BEIs® are without a numerical value and/or provide only qualitative estimates of exposure. These indices are useful to confirm that an exposure to a specific agent is occurring. The basis of each BEI® is provided in the Documentation. Air monitoring to determine the TLV® indicates the potential inhalation exposure of an individual or group. The internal dose for individuals within a workgroup may be different for a variety of reasons, some of which are indicated below:
    • Exposure by routes other than inhalation, usually dermal, is often a major reason why there is less than perfect concordance between air sampling and biological monitoring. This is often the strongest argument for doing biological monitoring.
    • Physiological makeup and health status of the worker, such as body build, diet (water and fat intake), metabolism, body fluid composition, age, gender, pregnancy, medication, and disease state.
    • Occupational exposure factors, such as the work-rate intensity and duration, temperature and humidity, co-exposure to other chemicals, and other work factors.
    • Nonoccupational exposure factors, such as community and home air pollution, water and food components, personal hygiene, smoking, alcohol and drug intake, exposure to household products, or exposure to chemicals from hobbies or from another workplace.
    • Methodological factors, which include specimen contamination or deterioration during collection and storage and bias of the selected analytical method.
    • Location of the air monitoring device in relation to the worker’s breathing zone.
    • Particle size distribution and bioavailability.
    • Variable effectiveness of personal protective devices.

    It is important that the reader consult the Documentation of the TLVs® and BEIs® to understand the importance of each of these factors for each particular agent.

    Specimen Collection

    Because the concentration of some determinants can change rapidly, the specimen collection time (sampling time) is very important and must be observed and recorded carefully. The sampling time is specified in the BEI® and is determined by the duration of retention of the determinant, modified in some cases by practicality (for example, if the peak level is expected several hours after the end of a shift). Substances and determinants that accumulate may not require a specific sampling time. An explanation of the BEI® sampling time is as follows:

    Sampling Time
    1. Prior to shift

    2. Prior to last shift
    3. Increase during shift
    4. During shift
    5. End of shift 
    6. End of the workweek
    7. Discretionary/Not Critical

    Recommended Collection
    16 hours after exposure ceases, but before any exposure on sampling day
    Prior to last shift of a workweek
    Requires pre- and post-shift sample collection
    Anytime after two hours of exposure
    As soon as possible after exposure ceases
    After four or five consecutive working days with exposure
    At any time*

    *These determinants have long half-lives and their levels may take weeks, months or years after a worker first begins their job to approach steady state and be comparable to the BEI®. Health professionals should note that if sequential samples taken early in a worker’s exposure career show a marked increase, an overexposure situation might be developing and must be addressed despite the values being below the BEI®.

    Urine Specimen Acceptability

    Urine specimens that are highly dilute or highly concentrated are generally not suitable for biomonitoring. The World Health Organization has adopted guidelines (without reference) for acceptable limits on urine specimens as follows:

    Creatinine concentration: > 0.3 g/L and < 3.0 g/L

    Specific gravity: > 1.010 and < 1.030

    Specimens falling outside either of these ranges should be discarded and another specimen should be collected when possible. 

    Some BEIs® for determinants whose concentration is dependent on urine output are expressed relative to creatinine concentration. For other determinants such as those excreted by diffusion into the renal tubules, correction for urine output is not appropriate. In general, the best correction method is chemical-specific, but research data sufficient to identify the best method may not be available. When the field data are only available as adjusted for creatinine, the BEI® will continue to be expressed relative to creatinine; in other circumstances, no correction is recommended, and the BEI® will be expressed as concentration in urine (e.g., μg/L). 


    "B" = background

    The determinant may be present in biological specimens collected from subjects who have not been occupationally exposed, at a concentration that could affect interpretation of the result. A “B” notation is assigned to a determinant when the observed 95th percentile value of a random sample, from  national population studies, such as the NHANES surveys, is more than 20% of the BEI®. When general population data are not available to make this assessment, the BEI® Committee may assign a “B” notation based on its interpretation of the available data in the scientific literature. In this case, the rationale for the notation is provided in the Documentation for the particular Index. Such background concentrations are incorporated in the BEI® value.

    “Nq” = Nonquantitative

    Biological monitoring should be considered for this compound based on the review; however, a specific BEI® could not be determined due to insufficient data.

    “Ns”  = Nonspecific

    The determinant is nonspecific, since it is also observed after exposure to other chemicals. 

    “Sq”  = Semi-quantitative

    The biological determinant is an indicator of exposure to the chemical, but the quantitative interpretation of the measurement is ambiguous. These determinants should be used as a screening test if a quantitative test is not practical or as a confirmatory test if the quantitative test is not specific and the origin of the determinant is in question.

    “Pop”  = Population based

    “Pop” indices are assigned when there are insufficient data to establish a numerical BEI® but where there are sufficient data on background levels in the general population. “Pop” values can be based on the 95th percentile of large studies of the general population, like the NHANES surveys by the CDC, or they can be based on nonoccupationally exposed populations from the scientific literature.
    “Pop” values are not health-based and are intended to give the health professional guidance regarding exposures that are likely to be occupational and not from the general environment. A measurement at or above a “Pop” level will have a high probability of resulting from an occupational exposure.  

    Quality Assurance 

    Each aspect of biological monitoring should be conducted within an effective quality assurance (QA) program. The appropriate specimen must be collected at the proper time, without contamination or loss, utilizing a suitable container. Donor identification, time of exposure, source of exposure, and the sampling time must be recorded. The analytical method used by the laboratory must have the accuracy, sensitivity, and specificity needed to produce results consistent with the BEI®. Appropriate quality control specimens should be included in the analysis, and the laboratory must follow routine quality control rules. Whenever possible, the laboratory should participate in an external proficiency program.

    The occupational health professional may also provide known challenge samples to the laboratory along with worker specimens (e.g., blanks, purchased specimens containing the determinant, or split specimens). These challenges will enable the occupational health professional to assess the ability to process, analyze, and report results properly, and to have confidence in their ability to estimate exposure.

    The most effective means for controlling laboratory quality is through an external QA/QC program.

    Application of BEIs®

    BEIs® are intended as guidelines to be used in the evaluation of potential health hazards in the practice of occupational hygiene. BEIs® do not indicate a sharp distinction between hazardous and nonhazardous exposures. For example, it is possible for an individual’s determinant concentration to exceed the BEI® without incurring an increased health risk. If measurements in specimens obtained from a worker on different occasions exceed the BEI®, the cause of the excessive value should be investigated and action taken to reduce the exposure. An investigation is also warranted if measurements in specimens obtained from a group of workers at the same workplace and workshift exceed the BEI®. It is desirable that relevant information on related operations in the workplace be recorded.

    Due to the variable nature of concentrations in biological specimens, administrative action should not be normally based on a single result, but on measurements of multiple samplings, or an analysis of a repeat specimen. However, it may be appropriate to remove the worker from exposure following a single high result if there is reason to believe that significant exposure may have occurred. 

    BEIs® apply to 8-hour exposures, 5 days per week. Although modified work schedules are sometimes used in various occupations, the BEI® Committee does not recommend that any adjustment or correction factor be applied to the BEIs® (i.e., the BEIs® should be used as listed, regardless of the work schedule).

    Use of the BEI® should be applied by a knowledgeable occupational health professional. Toxicokinetic and toxicodynamic information is taken into account when establishing the BEI®; thus, some knowledge of the metabolism, distribution, accumulation, excretion, and effect(s) is helpful in using the BEI® effectively. ACGIH® may be contacted for technical assistance on any BEI® issue. The BEI® is a guideline for the control of potential health hazards to the worker and should not be used for other purposes. The values are inappropriate to use for the general population or for nonoccupational exposures. The BEI® values are neither rigid lines between safe and dangerous concentrations nor are they an index of toxicity.


    It is essential to consult the BEI® Documentation before designing biological monitoring protocols and interpreting BEIs®. In addition, each BEI® Documentation now provides a chronology that traces all BEI® actions for the chemical substance in question.