Page:NIOSH Manual of Analytical Methods - Chapter F.pdf/4

 2. The method needs to be evaluated for the required specificity and possible interferences. If interferences from diet, drugs, alcohol, disease states, or other workplace chemicals or agents exist, they must be accounted for.

3. The method should have a sufficiently low limit of detection to differentiate exposed from nonexposed workers. A method developed when biological monitoring reference levels were higher may be inadequate for measuring exposures at and below the current guidelines.

4. Limitations of the sample matrix and its affect on the analysis need to be assessed. In general, blood serum and urine specimens require different sample preparations and may require separate methodologies to eliminate matrix effects.

5. Because of sample instability, some methods may be impractical or not feasible.

6. The method should have guidelines for interpretation of collected data. Such guideline are discussed in Interpretation of Results below.

7. To minimize the risk of harm to workers, when two biological monitoring methods will provide the same information, the less invasive method should be used. Thus, methods monitoring urine or exhaled breath are preferred over those monitoring blood.

Sampling Strategy. Strict attention to specimen handling and collection is essential for quality data. The analytical laboratory should be consulted for sampling instructions. Analytical methods should provide specific directions on the collection, storage, and transportation of specimens to the laboratory. Adherence to these directions is of the utmost importance to ensure sample integrity.

1. Timing of specimen collection should be for the timing of specimen collection, that work shift, at the end of the shift, or at the half-life of the xenobiotic, the less critical appropriate. The method should include instructions is, whether specimens should be obtained during the some other time during the work week. The longer is the timing of the collection [11].

2. The baseline of a biomarker should be evaluated when the toxicant accumulates in the body, as do cadmium, lead, and polychlorinated biphenyl [11]. The baseline should also be assessed, if there is large intersubject variability in the population, such as when pseudocholinesterase in plasma is measured.

3. Care should be taken not to contaminate the specimen with either chemicals or bacteria.

4. The proper preservative (for urine or blood samples) or anticoagulant (blood) should be used, if appropriate.

5. Stability of the biomarker is assured through proper storage and shipment of the specimen to the laboratory and proper storage by the laboratory.

Correction of Urinalysis Data for Dilution. Determination of biomarkers in individual urine samples is confounded by urine dilution, which can vary substantially with fluid intake and physical work load. In practice, this effect of urine dilution is reduced by adjusting the measured concentration of the biomarker to a normal value [5,27], such as:

1. Specific gravity. This adjustment is made by multiplying the measured concentration of the biomarker by the ratio of [(1.024 - 1)/(sp.g. - 1)], where sp.g. is the specific gravity of the urine sample and 1.024 is the assumed normal specific gravity value.

2.Urine output. The measured concentration of the biomarker is multiplied by the ratio R/0.05, where R is the output for the sample in liters per hour. The urine output for the sample is 1/15/98 Manual of Analytical Methods