What best describes the preclinical phase of disease?

• A. The phase after symptoms appear.
• B. Anytime after disease onset when there are no outward signs and symptoms.
• C. The phase during which treatment trials are conducted.
• D. The end stage of disease.

Answer: (B)

The preclinical phase is the period after disease onset when there are no outward signs and symptoms. In this stage the disease process has begun, but nothing is yet detectable clinically, so a person doesn’t feel ill even though pathology may be present. This phase ends when symptoms or signs first appear, marking the transition to the clinical (symptomatic) phase. The other descriptions don’t fit because they refer to stages after symptoms appear, to late-stage disease, or to research activities rather than a natural history stage.