Confirmatory and Repeat Testing

A screening result changes probability; it does not automatically establish disease. Screening tests are often designed to detect as many possible cases as possible, which means some reactive results will be false-reactive. A confirmatory test usually uses a different assay, target, or testing sequence to establish whether the screening signal represents the condition of interest. A repeat test asks a different question: does the same analyte remain abnormal when measured again on a new specimen? Repetition is useful when collection, transport, biological variation, or random analytic error could explain the first result. It is not a universal solution. If the assay is distorted by a haemoglobin variant or the marker persists after an old infection, repeating the same test reproduces the problem. Before ordering anything, verify the patient and specimen, review collection conditions and timing, check for haemolysis or other integrity flags, and compare the result with the current clinical picture and prior values. A delta check—a comparison with the patient’s previous result—can expose mislabelling, contamination from an infusing line, or an analytic problem. A physiologically impossible change should trigger...