Measurement of sialic acid in serum and urine: clinical applications and limitations.

Many recent studies have examined the sialic acid content of serum or urine in various pathological states. We have briefly reviewed the substances which contribute to the observed total sialic acid concentration, and given an overview of assay methods used. Three major areas of clinical interest in sialic acid metabolism are discussed. Serum total sialic acid, 'lipid-bound' and 'protein bound' sialic acid have all been proposed as tumour markers; but the usefulness of any of these tests is severely limited by changes due to accompanying inflammatory processes. Serum total sialic acid is not a valuable simple marker of an acute phase response. Urinary free and bound sialic acid measurements should be included in screening protocols for inherited disorders of lysosomal metabolism. Current developments in research and potential applications within the clinical biochemistry laboratory are briefly discussed.