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Heterophilic antibodies are human antibodies in a specimen which interact with assay antibodies to give false-positive or false-negative results. The heterophilic antibody may arise in a patient in response to exposure to certain animals or animal products, or to infection by bacterial or viral agents, or non-specifically. Among the anti-animal antibodies, the most common occurrence is of human anti-mouse antibody because of the wide use of murine monoclonal antibody products in therapy or imaging. Interferences from heterophilic antibody and anti-animal antibody in immunoassays are often grouped together as heterophilic antibody interference. Interference from auto-antibodies therapeutic anti-bodies, and rheumatoid factors (RF) is included in such interference. Such interferences are common with immunometric sandwich assays, but encountered only infrequently with competition (most common assay used in therapeutic drug monitoring/drugs of abuse testing) assays. Sample dilution, removal of interfering antibodies, or treatment of specimen with a heterophilic blocking agent prior to assay, has been recommended to remove heterophilic antibody interference. Thus, heterophilic antibodies are absent in the protein-free ultrafiltrate, and monitoring free drug concentration also eliminates this interference. [ABSTRACT FROM AUTHOR]

Among the endogenous interferents affecting assay results, the most common are bilirubin, hemoglobin, lipids, and paraproteins. These interferents may affect therapeutic drug monitoring (TDM), drugs of abuse (DAU) testing, and toxicology assays of any format where the sample is used directly for analysis without any pretreatment of specimen. Immunoassays are commonly used in clinical laboratories where analyte-specific antibody or binding agents are used to estimate the analyte concentration in the specimen. Some enzyme and chemistry assays are also utilized in TDM and DAU analysis. Such assays use various types of signals, the most common being colorimetry, fluorimetry, and chemiluminescence. Assays may be prone to interference depending on the format or label used. Commercial assay kits report the result of such interference in the kit inserts (up to levels of >20 mg/dL bilirubin, >500 mg/dL hemoglobin, and >1000 mg/dL lipids). The interference is caused by the optical, fluorescent, or chemiluminescent properties of these interferents. Thus, bilirubin interferes by its absorption and fluorescence properties, hemoglobin by its absorption, fluorescence and chemiluminescence properties, and lipids interfere mostly from their light-scattering (turbidity) properties. Bilirubin and hemoglobin may also interfere because of side reactions in the assay. Modern auto-analyzers can detect all three interferents and flag the results. Flagged results should be carefully reviewed for the accuracy. Both hypo- and hyper-proteinemia can affect assay results. Paraproteins interfere in many assays by precipitating out during the sample blanking step thus producing false results. Another source of interference may be from probe (sample or reagents) or reaction cuvettes carryover contamination in random-access auto-analyzers. If the validity of test results is questioned, the assay should be repeated either by removing the interferent from the sample or by using different method which is known to suffer less from that type of interference. [ABSTRACT FROM AUTHOR]

Significant improvement in prostate cancer diagnosis and monitoring of therapy has been made possible by the discovery and use of prostate-specific antigen (PSA) measurement in patient serum. Widespread use of the PSA test has resulted in significant prevention of death from this major cancer disease in males. PSA measurements are used not only to stage the patient's cancer or monitor therapy but also to screen for patients who need the prostate biopsy, a costly and painful process. There are controversies present with regard to the serum PSA cutoff (4.0 µg/mL), above which level the cancer is suspected. A lower cutoff (2.5 µg/mL) improves sensitivity of cancer detection but reduces the specificity, because benign diseases of the prostate also might raise serum PSA. Measurement of serum PSA isoforms—complex or free PSA—has been reported to improve the efficiency of the PSA test. The main way serum PSA is measured is by immunoassays, of which many commercial methods, applied on automated systems, are available. It is, however, important to consider issues like hook and heterophilic interference that could affect some PSA assays. Future improvements in prostate cancer diagnosis include markers for aggressive than the slow-growth cancer and use of multiple markers to improve the efficiency of the diagnosis. [ABSTRACT FROM AUTHOR]