OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at http://www.osha.gov.

July 20, 1989




SUBJECT:          Letter from Dr. Glen Douglas Re:  Interpreting Blood
                 Test Parameters Under Benzene Standard

As requested, attached is a copy of our response to the letter you forwarded us on May 22, from Dr. Glen Douglas of Houston, Texas, in which he raised questions relative to the blood testing requirements of the benzene standard, 29 CFR 1910.1028.

We believe you will find our response to be self-explanatory. If you have any questions, please feel free to contact Melody Sands of my staff at (FTS) 523-8036.


July 20, 1989

Glen A. Douglas, M.D.
Post Office Box 24092
Houston, Texas 77229-4092

Dear Dr. Douglas:

This is in response to your letter of May 14, to the Occupational Safety and Health Administration (OSHA) Regional Office in Dallas. Your letter, which had been forwarded to us for reply, sought specific guidance relative to OSHA'S standard for occupational exposure to benzene, 29 CFR 1910.1028.

The Medical Surveillance sections (i)(2) and (i)(3) of the standard require that during both the initial exams and periodic exams "a complete blood count including a leukocyte count with differential..." be performed. You questioned whether a manual differential was acceptable, pointing out that cell abnormality was notable only through the performance of the manual test. The language of the standard does not designate which type must be performed and so therefore either type would be acceptable. However, as with many OSHA health standards, in terms of enforcement of this requirement, the benzene standard sets only the minimal criteria that must be met in order to be in compliance with the requirements of the rule. If, in your opinion as the physician responsible for the employees' medical surveillance program, performing a manual differential provides you superior information on the effects of benzene exposure on the exposed employees than automated counting, you are encouraged to continue to perform the manual tests. Again, however, you are not required to do so.

Additionally, according to section (i)(7)(i)(B) of the standard, the employer must provide affected employees with the physician's written opinion as to whether or not "the employee has any detected medical conditions which would place the employee's health at greater than normal risk of material impairment from exposure to benzene." If a manual differential is performed that indicates the presence of any cell abnormalities, and since changes in cell morphology such as the kind that might be noted during a manual differential may be indicative of a hematological abnormality, the physician would need to report this finding in his written opinion.

Your second question concerned the language in Appendix C - Medical Surveillance Guidelines for Benzene, section V.B.2, which requires that the peripheral blood smear may be prepared from "fresh, uncoagulated blood" except under "certain limited conditions" when the smear may be prepared from a blood sample anticoagulated with EDTA. You questioned what the "limited conditions" were and offered that the use of anticoagulated blood was routine clinical practice. As result of discussions with personnel from OSHA's Office of Occupational Medicine and Directorate of Health Standards, we were unable to determine the derivation of the qualification that blood should, only under "limited conditions," be anticoagulated. Our staff physicians agreed that it is indeed routine procedure for blood samples to be anticoagulated before examination, since it is rare that blood samples are able to be analyzed immediately after the sample is collected. It is, therefore, perfectly acceptable to routinely prepared blood smears that have been made from blood anticoagulated with EDTA.

We hope this discussion adequately addresses the concerns you raised. Please feel free to contact us again if you have any further questions.


Patricia K. Clark, Acting Director
Directorate of Compliance Programs