Analytical error and interference in immunoassay: minimizing risk

Although generally robust, immunoassays remain vulnerable to occasional analytical errors that may have serious implications for patient care. Sporadic errors that occur as a result of properties of the specimen are particularly difficult to detect. They may be due to the presence of cross-reacting substances, antianalyte antibodies or antireagent antibodies, all of which may lead to erroneously high or low results. Low results may be observed for tumour markers due to high-dose hooking in the presence of very high analyte concentrations. Erroneous results can occur unexpectedly with any specimen and there is no practical means of identifying specimens likely to cause problems in immunoassays. The possibility of interference should always be considered when results do not appear to be in accord with the clinical picture. Errors can occur in even the best-managed laboratories and their early investigation is always desirable. If there is any doubt whatsoever about a result, clinical staff should be encouraged to contact the laboratory. Investigations for possible interference that can be undertaken in most laboratories include testing for linearity on dilution, recovery experiments, treatment with heterophilic blocking tubes and confirmation using a different method. It may be desirable to consult specialist laboratories if more complex studies are necessary. Informing clinical and laboratory staff of the ever-present possibility of unexpected interference, ensuring brief clinical details are available to laboratory staff, and above all facilitating excellent communication between laboratory and clinical staff are key to minimizing the risk of clinical mismanagement due to unsuspected interference.