Determination of CA19-9-EIA False-Positive Specimens in Liver Disorders and Their CA19-9 Molecular Weights

Abstract

We have previously reported that CA19-9 values obtained with the enzyme immunoassay (EIA) method were higher than those obtained with radioimmunoassay (RIA) for patients with liver disorders. In this report the following findings are presented:
1) When screening of sera from 48 patients with liver disorders was performed using our criteria, 19 specimens were found to have more than 2-fold higher CA19-9 values as measured by EIA than as measured by RIA.
2) These 19 specimens with large discrepancies in CA19-9 values each had slightly elevated levels, in the range 100-500U/ml, of CA19-9 on measurement by EIA. They had been obtained from patients with chronic hepatitis or cirrhosis of the liver.
3) The molecular weight of CA19-9 was determined by high-performance liquid chromatography (HPLC). While the molecular weight of CA19-9 in two patients with carcinoma, which was used as a control, was approximately 1000kD, most of the sera with discrepancies in CA19-9 values noted above had CA19-9 of two molecular weights, one high, at 1300-1400kD, and one low, at 400-800kD.
4) When account is taken of the unsatisfactory degree of resolution in the high molecular weight region on HPLC, the above findings suggest that the low molecular weight components of CA19-9 react in EIA measurements, yielding false-positive results.