The Specific Gravity Adjustment in Urinalysis

Over twenty years’ experience with the specific gravity adjustment in urinalysis has been reviewed. It is concluded that this method of expressing results of analysis of urine for heavy metals, solvent metabolites, and radioactive isotopes is preferable to the unadjusted concentration. Complicating factors, which may affect the validity of specific gravity-adjusted values, include variations in diet and degree of sweating. The adjustment fails when applied to samples containing sugar. As between measurement of rate of excretion per 24 hours and the specific gravity adjustment, the latter is generally preferable for practical reasons. In extreme cases values obtained by the two methods vary by a factor of five or more. In such situations the best method of expressing findings is uncertain.