Concentration adjustment of spot samples in analysis of urinary xenobiotic metabolites

The reliability of the adjustment for the reduction of concentration-dilution effects in urinalysis of spot specimens was evaluated; 95.4% of spot specimens showed a creatinine concentration between 0.5 and 3 g/liter, whereas 59.8% showed a specific gravity between 1.010 and 1.030. Only 6% of the specimens exceeded the specific gravity of 1.035 corresponding to a creatinine concentration of 3 g/liter. Therefore, an acceptable value for specific gravity in spot specimens of 1.035 is proposed. Although either specific gravity or creatinine provides a reliable mean of adjustment, creatinine is preferred because it has fewer physiological confounding factors.