A simple procedure is described for the detection of
sialic acid in serum. After a direct addition of Ehrlich
reagent to serum and an incubation at 56 degrees C for eight hours, the resulting mixture is diluted with saline. After centrifugation, the color in the supernatant is determined at 525 nm in a spectrophotometer. Serum
sialic acid was significantly greater in
cancer patients than in normals.
Cancer patients with
metastases had significantly greater
sialic acid than
cancer patients without
metastases. In two
cancer patients,
sialic acid levels returned to normal after surgery. The diagnostic usefulness of 95.6% was similar to that reported with
lipid-soluble
sialic acid and seemed to be superior to CEA and other
tumor antigens associated with a limited spectrum of
tumors. However, patients with inflammatory diseases such as
arthritis,
Crohn's disease and
psoriasis also showed elevated
sialic acid levels. Ultrafiltration showed that almost all of the
sialic acid was retained on an Amicon filter, which suggests that
sialic acid was bound to a macromolecule. A quality control serum run 25 times had a coefficient of variation (CV) of 8.4% and the same serum ran on 42 days had a CV of 11.6%.