Polyethylene glycol precipitation is a useful method for excluding the interference of unexplained elevated CA 19-9.

With improved living standards and increased health awareness among Chinese residents, carbohydrate antigen 19-9 (CA 19-9) has become a routine marker in health examinations. Elevated CA 19-9 levels are frequently observed in clinical practice. Although chemiluminescence technology is widely recognized for its high sensitivity and specificity, it cannot eliminate interference, which may lead to deviations and misdiagnoses. This study aims to find a simple and effective method to confirm and exclude the interference of CA 19-9 on the Abbott platform. 342 individuals with unexplained elevated CA 19-9 in serial determinations for more than 6 months were included as cases. Serum samples from individuals with persistently elevated CA 19 -9 levels were evaluated via sialidase treatment, polyethylene glycol (PEG) precipitation, gel filtration chromatography (GFC), gradient dilution assays, heterophile antibody blocking assays and rheumatoid factor titer assays. Out of 342 individuals with elevated CA 19-9, 77 cases were confirmed as interferent by the sialidase treatment. There was a significant consistency between the PEG precipitation and sialidase treatment results (kappa = 0.920). Compared with the sialidase treatment method, the specificity of the PEG precipitation method was 96.2%, and the sensitivity was 100%. When the cutoff value for the CA 19-9 recovery after PEG precipitation was below 37.9%, the area under the curve (AUC) was highest at 0.993 (95% CI 98.5-99.8%). The PEG precipitation method is useful and reliable for patients with unexplained elevated CA 19-9. This method could effectively identify the interference, reduce clinical misdiagnosis, alleviate unnecessary financial burdens on patients.