Retrospective Approach to Evaluate Interferences in Immunoassay

BACKGROUND Despite the increase in sensitivity and specificity of immunoassay technique over years, analytical interference remains to be major area of concern. The interfering substances are endogenous substances that are natural, polyreactive antibodies as heterophilic or auto antibodies, or human anti-animal antibodies together with other unsuspected binding proteins that are unique to the individual. Interfering substances can interfere with the reaction between analyte and reagent antibodies in immunoassay resulting in false positive or negative values. This ultimately results in misinterpretation of patients reports and finally to wrong course of treatment. OBJECTIVE In our study, we used a retrospective approach to find out the extent of interferences and type of interferences in some cases during our routine practice. METHOD The immunoassay reports which were clinically not correlating were retrospectively evaluated after discussion with the clinician. Over a period of six month a total of 42 samples were evaluated for interference for different immunoassay parameters such as Beta HCG, Estradiol, CA 125, AFP, prolactin, Hepatitis B Surface antigen (HbSAg) and troponin I. The samples were treated with commercially available antibody blocking agents and were reanalyzed. Commercially available diluents were used in some cases to evaluate high dose hook effect. Different platform, methodology and reagents were used for re -analysis. RESULTS Out of 42 samples, 19 were found to be affected by interferences The data obtained for interferences was as follows beta HCG - 6 samples (2 positive and 4 negative interference); estradiol - 3 samples (2 positive and 1 negative interference); CA-125-3 samples (2 positive and 1 negative interference), Alfa Feto Protein - 2 samples (2 positive interference); prolactin - 1 sample (positive interference); Hepatitis B Surface antigen - 1 samples (negative interference); troponin I - 2 samples (positive interference). CONCLUSION Despite the use of state of the art laboratory equipments, chances of interference in immunoassay analysis resulting from endogenous substances could not be ruled out. In conclusion, thorough evaluation of all immunoassay reports should be carried out in cases of suspected interference.