The clinical chemistry of inorganic sulfate

Although inorganic sulfate is an essential and ubiquitous anion in human bi ology, it is infrequently assayed in clinical chemistry today. Serum sulfat e is difficult to measure accurately without resorting to physicochemical m ethods, such as ion chromatography, although many other techniques have bee n described. It is strongly influenced by a variety of physiological factor s, including age, diet, pregnancy, and drug ingestion. Urinary excretion is the principal mechanism of disposal for the excess sulfate produced by sul fur amino acid oxidation, and the kidney is the primary site of regulation. In renal failure, sulfoesters accumulate and hypersulfatemia contributes d irectly to the unmeasured anion gap characteristic of the condition. In con trast, sulfate in urine is readily assayed by a number of means, particular ly nephelometry after precipitation as a barium salt. Sulfate is most commo nly assayed today as part of the clinical workup for nephrolithiasis, becau se sulfate is a major contributor to the ionic strength of urine and alters the equilibrium constants governing saturation and precipitation of calciu m salts. Total sulfate deficiency has hitherto not been described, although genetic defects in sulfate transporters have been associated recently with congenital osteochondrodystrophies that may be lethal. New insights into s ulfate transport and its hormonal regulation may lend to new clinical appli cations of sulfate analysis in the future.