When is testing indicated based on pretest probability of disease?

Testing is often indicated when the pretest probability of disease is moderate because this is where the balance between benefit and risk is most favorable. In such cases, a moderate pretest probability suggests that there is a reasonable likelihood of the disease being present, which justifies the pursuit of further diagnostic testing. The results of the testing can provide more clarity, influence management decisions, and provide necessary information for both the healthcare provider and the patient.

When the pretest probability is high, there may be less need for testing if the clinical presentation strongly indicates the disease; the clinical diagnosis may suffice to guide treatment. Conversely, when the probability is low, testing may not be warranted, as the likelihood of a positive result is not high enough to justify the costs, risks, or potential harms of the testing. In asymptomatic patients, the lack of symptoms usually indicates a low pretest probability for most diseases, further decreasing the rationale for testing in that scenario.