An Immunoassay for Human Chorionic Gonadotropin in Cerebrospinal Fluid: Validation of a Modified-Approved Method for Accreditation by the College of American Pathologists

Background Human chorionic gonadotropin (hCG) detection in cerebrospinal fluid (CSF) can provide additional value in the diagnosis of germinoma. However, matrix effects can influence the results when alternative sample types are used. Therefore, modified-cleared/approved methods, which are standard methods used outside their intended scope, are of interest. The aim of the present study was to establish a model to validate modified-approved methods in agreement with the College of American Pathologists (CAP) accreditation requirements. Methods Concentrations of hCG in CSF were determined by means of electrochemiluminescence immunoassay using a Roche Cobas e 602 immunoassay analyzer. Based on the intended use, the following performance characteristics were evaluated: precision, the limit of quantitation (LoQ), and the analytical measurement range (AMR). The reference interval (RI) was also established. For the clinical application study, CSF and serum hCG were measured in 10 patients diagnosed with germinoma. Results The intra- and inter-assay precisions at two levels (10, 250 IU/L) were 0.64 and 0.57% and 4.26 and 3.54%, respectively. The LoQ for hCG was determined to be 0.25 IU/L. The AMR was set from 0.2 to 1,200 IU/L. The RI for hCG in CSF was below 0.40 IU/L. The CSF hCG levels of 10 patients were all above 0.4 IU/L before therapy. Conclusion Modified-approved methods were validated and showed that the quality specifications of the medical laboratory have a positive value in the clinical context. The illustration of quantification of hCG in CSF resulted in compliance with the CAP accreditation requirements.