We all know how the antibodies of our immune system protect us from microbial harm and pathology. We also know the history of immunoassays, and how this technology makes very specific and sensitive detection possible. The highly specific and strong reaction between antigens and their corresponding antibodies enables laboratories to measure biomarkers in many kinds of biological fluids. Because of immunoassays, we can detect biomarkers quickly and efficiently diagnose many diseases, making them a cornerstone of modern medicine.
But at the same time, antibodies also have a dark side. One example of this is the way in which heterophilic antibodies and paraproteins present in patient samples. These interact with assay reagents—not only immunoassays, but many chemistry assays as well—to give erroneous results, resulting in misdiagnosis and compromising patient care. Sutirtha Chakraborty, MD, and Bernard Cook, PhD, explored these troublesome interferences and their results in yesterday’s short course, “Endogenous Antibody Interferences in the Chemistry Laboratory: Trouble from the Inside.”
Chakraborty described how the interference of monoclonal proteins in clinical chemistry assays could be detected and solved. Such interference may often be detected when the lab result does not match the clinical picture. He also talked about false positive inorganic phosphorous (IP) results in serum samples from patients with monoclonal gammopathy. IP is commonly analyzed by molybdate reaction under acidic condition. Monoclonal paraproteins may precipitate under such condition, generating false positive results. Chakraborty described a method for removing the serum proteins first, either by PEG-6000 precipitation or by ultrafiltration. In his studies, the protein-free supernatant had the correct IP results.
Such interference may happen for many other chemistry assays—bilirubin, HDL-cholesterol, calcium, uric acid, electrolytes, glucose, albumin, C-reactive protein, ferritin, urea, creatinine, and thyroxine, for example. Laboratories can deal with this interference by removing proteins before analysis or by alternate methods.
For his part, Cook explained how heterophilic antibodies can interfere in immunoassays. He gave examples where false positive serum hCG led to unneeded surgery and/or chemotherapy for suspected choriocarcinoma. In these examples, the serum samples gave different results in other hCG assays and did not dilute linearly. Also, urine samples from these patients did not show hCG or its degradation products. The conclusion, Cook explained, was that protocols for diagnosis and treatment of choriocarcinoma must include a compulsory test for hCG in urine. Cook also elucidated the use of antibody fragments and other blockers to neutralize serum heterophilic interference.
The take home message from this short course was that laboratorians must watch for lab results that do not agree with the clinical picture. Laboratories can take steps than can remove or minimize the interferences from heterophilic antibodies or monoclonal proteins in serum or plasma samples. Yes, when it comes to immunoassays, laboratories face “trouble from within.” However, with the right knowledge, laboratories can still succeed against such troubles.