Medical Decision Limits

true positive - result at or above the decision limit in a patient who has the disease false positive - result at or above the decision limit in a patient who does not have the disease true negative - result below the decision limit in a patient who does not have the disease false negative - result below the decision limit in a patient who has the disease

Along with determining the reference ranges to correlate with absence of disease, it is also helpful for physicians to have a cutoff value to associate with specific diseases. In fact, that is the basic purpose of laboratory tests with the goal of detecting disease in its early stages. For example, a fasting plasma glucose of 126 mg/dL is used to classify diabetes. This is an example of a medical decision limit or cutoff. It helps to differentiate presence of a particular disease from absence of that disease. Medical decision limits are determined by quantifying the analyte of interest in a sampling of a patient population with the disease and a sampling of those without the disease. Next, with the results obtained from the analysis, the patients are classified based on disease presence and test result using a presumed medical decision limit. The four diagnostic categories are true-positive, false-positive, true-negative, and false-negative.

A true positive (TP) is a patient with the disease and a laboratory result at or above the medical decision limit. A true negative (TN) is a patient without the disease and a laboratory result below the medical decision limit. A false positive (FP) is a patient with a laboratory result above the medical decision limit but who is found not to actually have the disease, while a false negative (FN) is a patient with a laboratory result below the medical decision limit but who actually does have the disease. Good medical decision limits exhibit low diagnostic false positives and false negatives (such as 2% or less). Table 2-8 shows an example of the classification of patients based on fasting plasma glucose (FPG) and diagnosis of diabetes mellitus (DM). This information is then used to calculate the diagnos-

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Responses

  • vesa
    What is decision limit?
    6 years ago

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