A New Method for Measuring Sialic Acid Levels in Serum and Its Application to Rheumatic Fever1

Abstract

Previous reports (1-4) have indicated the clini- cal usefulness of a color reaction given by serum with the diphenylamine reagent of Dische.It has been shown that the purple color produced in this reaction is probably due to the presence of a deoxyhexose structure in the sialic acid molecule (5).Sialic acid, or a closely related substance, appears to be a common constituent of mucopro- teins (glycoproteins) including orosomucoid of serum (6, 7).The color produced in the diphenyl- amine reaction reflects the concentration of the mucoproteins in the serum being tested.In our experience, and as reported by Anderson and Maclagan (8), the color developed with diphenyl- amine appears to be a specific reaction of muco- proteins.An elevation in the mucoproteins found in the alpha globulin fraction of serum is characteristic of many diseases (7).As pointed out in a previous report (4) a con- stant feature of the diphenylamine reaction was the concomitant rise in the color index of the "serum blank" associated with the increased color intensity of the serum samples tested.The "serum blank" in this instance was the combination of depro- teinized serum with the sulfuric acetic acid mix- ture which did not contain diphenylamine.This report will consider the chemical and clini- cal aspects of the "serum blank" reaction.It will be shown that the color produced when a mixture of sulfuric and acetic acids is heated with the de- proteinized serum sample is also probably due to sialic acid.The simplicity of the test suggests its usefulness as a new method for measuring the in- tensity of inflammation.

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