Rational Use of Diagnostic Tests
should be made aware that more expensive, more invasive tests may follow if diagnosis is not
achieved. For example, fine needle aspiration and cytologic evaluation are often
recommended prior to surgical removal and biopsy of a mass. For many tumor types, such as
lymphoma and mast cell tumors, diagnosis is usually easily achieved with cytology, and
knowledge of the diagnosis prior to surgery augments treatment planning. For spindle cell
tumors, such as fibrosarcoma or hemangiopericytoma, diagnostic cytologic samples are not
always obtained, and a biopsy may need to be performed to achieve a definitive diagnosis.
Useful characteristics of diagnostic tests
Accuracy and Precision
Accuracy is the measure of a test result's accordance with results determined by a gold
standard. It is the frequency with which a given test correctly identifies a patient as having a
disease, or put another way, how closely the mean of test data points accords to the mean of
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