In Acute Illness 1. If treatment would be altered by knowledge derived from a lab test, then it should be done. An example of this would be a test for ova and parasites in a stool sample from a child with severe or protracted diarrhea. If the prognosis depends on a simple, noninvasive lab test, then it may be beneficial.
Examples are an office strep test or throat culture or a mononucleosis blood test.
If treatment would not change given the knowledge derived from the test, then it is probably not necessary. This includes skin culture in a localized infection, however - 4. If a diagnosis is needed to understand the patient's condition , then it should be performed. Examples are a urine culture in an infant's unexplained fever, a pregnancy test in adolescent secondary amenorrhea, or a sedimentation rate and rheumatic workup for joint pain. If the condition is possibly life-threatening, then a complete diagnostic workup is essential.