Micro-scale blood lead determinations in screening: evaluation of factors affecting results.

The Delves micro-scale technique for blood lead analysis is an accurate method for screening capillary blood specimens, obtained by fingerstick, for lead intoxication. Results are affected by the age of cup, loop, and hollow-cathode tube and by the spatial relationship between optical tube and cup. Because the glass in many commercially available capillary tubes (used in specimen collection) contains lead and cannot be decontaminated, a lead-free glass tube must be used. A solution of citric acid in ethanol (20 g/liter) effectively cleanses the puncture site. A double-blind study of 207 specimens gave a mean value of 276.6 plus or minus 105.8 mug/liter (1SD) for the micro-scale method vs. 273.2 plus or minus 99.0 for a macro-scale method. The mean coefficent of variation for the micro-scale method was 5.75 percent plus or minus 1.9 (SD). We conclude that values of 480 mug/liter or below are not "toxic" (i.e., are significantly less than 600 mug/liter, the value at which therapy is begun). The method is shown to be satisfactory as a screening procedure and for confirming lead analyses done by other methods.