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 https://www.osha.gov.

June 15, 1994

Anton D. Check
Safety and Health Specialist
Degussa Corporation/Metal Group
3900 South Clinton Avenue
South Plainfield, NJ 07080

Dear Mr. Check:

This letter is in response to your questions of June 9, 1994 regarding cadmium biological monitoring. Your questions pertain to accurate urinary sampling. The short answers to your questions are as follow: 1) standard medical practice specifies that when specific gravity is low (e.g., less than 1.008), urine samples are too dilute for accurate laboratory analysis; 2) epidemiological studies of cadmium-induced renal damage, summarized in the preamble to the final cadmium standards, specify that Beta-2 microglobulin (B(2)-M) will degrade in acidic urine, with pH less than 5.5; and, 3) since both cadmium in urine (CdU) and B(2)-M are standardized to grams of creatinine (CRTU), artificially low CRTU will inflate CdU and B(2)-M calculations. Additional information follows.

OSHA has received several questions concerning overhydration and its effects on urinary sample results. In Appendix F of the cadmium standard, OSHA specified a number of sample collection and handling procedures for enhancing the accuracy of blood and urine samples taken as part of the cadmium biological monitoring program. Under section 3.4.1. of Appendix F (57 Federal Register 42424), for example, employees are advised to void, drink a large glass of water, and then provide a urine specimen within an hour. OSHA now believes this prehydration procedure may lead to overhydration in some instances, thereby lowering CRTU levels.

In response to the hydration problem noted in the previous paragraph, OSHA's current recommendation is that employees provide a urine sample for cadmium, B(2)-M, and CRTU for laboratory analyses without first drinking a glass of water. If screening tests show that this first urine sample is too dilute (i.e., a specific gravity of less than 1.008), then a second urine sample should be collected at the next void with no intervening hydration. Only if screening tests demonstrate that this first urine sample is too acidic (i.e., a pH of less than 5.5) should the employee drink water prior to collecting the second urine sample; in this case, the employee should drink no more than an eight-ounce glass of water, and the second urine sample should be collected after waiting at least one (1) hour. Urine from the second void should be used for laboratory analysis of CdU, B(2)-M, and CRTU if screening tests show that specific gravity and pH levels are at or above 1.008 and 5.5, respectively. If the CRTU level of the second void remains too low, the employee should wait one (1) day and provide a third sample. This third sample should be collected without first drinking a glass of water. If screening tests indicate that the CRTU levels is still too low, then the renal function of the employee should be evaluated medically to rule out other possible etiologies that may account for these effects. Only after these etiologies have been ruled out should a fourth urine sample be collected; this sample should be treated in the same manner as the first sample described earlier in this paragraph. Under no circumstances should samples that are too dilute or too acidic be submitted to a laboratory for analysis.

If you have any questions or comments, please contact my office at 202-219-5003.


Melissa McDiarmid, MD, MPH
Office of Occupational Medicine
200 Constitution Avenue, N.W.
Washington, D.C. 20210