Subclinical

Subclinical refers to a stage of disease in which pathological changes are present and detectable by laboratory tests or imaging, but clinical symptoms are not evident to the patient. It contrasts with clinical disease, where symptoms drive diagnosis. Subclinical conditions may precede overt illness and, in some cases, progress to symptomatic disease; in others they may remain stable for long periods or reflect incidental findings during routine screening.

Common uses of the term include subclinical hypothyroidism and subclinical hyperthyroidism, characterized by abnormal thyroid-stimulating hormone levels with normal thyroid hormone concentrations and little or no symptoms. Subclinical atherosclerosis refers to detectable vascular changes that have not yet produced cardiovascular symptoms. Subclinical infections are infections that are detected by screening tests or laboratory analysis without producing noticeable illness, though they may progress to symptomatic disease if untreated.

Diagnosis relies on abnormal test results, screening programs, or imaging findings, rather than patient-reported symptoms. The course of subclinical disease varies by condition; some subclinical states are monitored with regular testing and risk-factor modification, while others may warrant treatment to prevent progression to overt disease. Decisions are individualized and depend on age, comorbidities, risk of progression, and potential treatment benefits and harms.

Subclinical findings are important for understanding disease progression, guiding clinical decisions, and informing public health strategies. They underscore the gap between measurable disease processes and clinical presentation and highlight the value and limits of screening.