Internists repeat C-reactive protein a few days after an emergency admission almost as a reflex, and many of us act on the second value: a fall reassures, a rise prompts a rethink. Yet the evidence behind that reflex is thinner than the habit suggests. Serial measurement has been studied mainly in intensive care and pneumonia cohorts of a few hundred patients, in which the exposure is usually collapsed into “responders” and “non-responders” [1–4], a practice that discards information and cannot tell a clinician how much the risk actually differs [5].
