Serological Tests for the Diagnosis of Infectious Diseases

Recent automated systems for the serological tests employing chemiluminescence immunoassay or electrochemiluminescent immunoassay give results within 30 minutes with high sensitivity and accuracy. However, false positive results are inevitable in serological screening for an infection due to the trade-off between sensitivity and specificity. A titration test has been used to confirm the screening results, but it is rarely performed. Instead, molecular tests are preferred in these days. Immunoassays were mostly qualitative in the past; however, quantitative kits have been developed and released on the market. The calibration step is necessary to report results quantitatively. As the calibration curve of an immunoassay is non-linear, four parameter or five parameter logistic models are adopted. Analytical measurement range (AMR) verification should be performed periodically at least every six months in order to report quantitative results. Quantitative reporting is feasible only within a linear range that is verified by AMR evaluation. A new concept of quantitative measurement/qualitative reporting in immunoassays is introduced. Qualitative reporting even after the quantitative measurement has the advantage that periodic AMR verification is not required. This category can be applied if the accurate quantitative value is not clinically significant. Lately, the market of point-of-care testing (POCT) is growing rapidly due to an increasing need. Nevertheless, the performance of the serological POCT kits is much lower than that of automated systems for central laboratories. This limits the broad utilization of POCT, and thus research for enhancing its performance should continue.