A patient at increased risk for interference in an immunoassay:
(1) multiply transfused patient
(2) patient with a history of previous false positive or negative assay
(3) multiparous woman
(4) patient with autoimmune disorder, especially rheumatoid arthritis
(5) patient with an acute infection, often viral
(6) recent immunization
(7) malignant disorder, especially multiple myeloma, malignant lymphoma, or CLL
(8) immunosuppression or immunodeficiency
Clinical features:
(1) A test finding does not match the clinical findings.
(2) The unexpected test finding is seen in a repeat specimen.
(3) The test utilizes an antibody in the detection system (to drug, serum protein, hormone, tumor marker, antibody to an infectious agent).
Possible solutions:
(1) Test for possible interfering compound (rheumatoid factor, heterophile antibody, etc.).
(2) Modify the test protocol (alter steps, switch to antibody from different species, use a blocking agent).
(3) Repeat testing later, if associated with a period of activity in an autoimmune disease or if suspect an infection with prior to development of the immune response.
(4) Perform serial dilutions of the specimen. Dilution of an interfering substance may give nonlinear results (a small dilution can result in the interference disappearing).
(5) Perform the assay using a different immunoassay platform.
