Laboratory investigations - inflammatory markers

CRP and ESR

ESR and CRP are the two standard non-specific markers of systemic inflammation - both rise with a wide range of infective, inflammatory, and malignant processes, and neither identifies a specific cause
Widely used as a first-line screen when systemic inflammatory disease is suspected, and to monitor treatment response in known inflammatory conditions

CRP - an acute-phase reactant produced by the liver in response to IL-6; rises and falls rapidly (within hours-days), making it useful for tracking acute change
ESR - indirectly reflects plasma protein changes (mainly fibrinogen) that promote red cell rouleaux formation and faster sedimentation; rises and falls more slowly than CRP, and is also affected by factors unrelated to inflammation (age, anaemia, pregnancy, obesity all raise ESR independently)

Discordant CRP/ESR patterns are informative: markedly raised ESR with a relatively normal CRP is classic for multiple myeloma (paraprotein drives rouleaux without a true acute-phase response) and some connective tissue diseases; SLE characteristically produces a raised ESR with a disproportionately normal/mildly raised CRP unless there is superimposed infection or serositis
Extremely high ESR (>100mm/hr) should prompt consideration of giant cell arteritis, malignancy, or severe infection

Trend (not a single value) is what guides management in most chronic inflammatory disease - CRP is generally preferred for monitoring acute response to treatment given its faster kinetics

A normal CRP/ESR does not exclude significant disease (some conditions, including SLE without serositis, can have normal markers), and both are non-specific - always interpreted alongside the clinical picture, never in isolation

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