C-reactive protein, a fast-rising blood marker of inflammation or infection.
What it is
C-reactive protein (CRP) is made by the liver within hours of an inflammatory signal (especially interleukin-6). Standard CRP is reported in mg/L. High-sensitivity CRP (hs-CRP) assays measure much lower concentrations and are sometimes used in cardiovascular risk research; they are not interchangeable with acute infection cut-offs.
CRP does not tell you where inflammation is or what caused it. It is a non-specific flare detector used alongside symptoms, examination, and other tests.
CRP transcription in hepatocytes rises within 6–8 hours of an IL-6 signal and can increase a hundredfold in severe bacterial infection. It falls with a half-life of about 19 hours once the trigger settles: faster than many other acute-phase proteins.
Why it matters
CRP often rises with bacterial infection, inflammatory flares, tissue injury, and post-operative states, then falls as the trigger settles, which is why serial values can track recovery. Mild elevations have many explanations; very high values usually prompt a search for significant infection or inflammation.
A normal CRP does not exclude all disease. Conversely, a raised CRP after a hard race, dental infection, or vaccine can be short-lived. Lifestyle links include smoking, central adiposity, and poor sleep, but “lowering CRP” is not a substitute for investigating a clinically important rise.
Never start or stop prescribed medicines based on a consumer CRP reading alone.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
CRP binds to damaged cells and pathogens and helps the innate immune system clear debris. The same acute-phase response shifts liver protein production (up CRP, often down albumin) and can redistribute iron, which is why ferritin and iron tests need inflammatory context.
Chronic low-grade elevation is associated in population studies with higher cardiometabolic risk, but that epidemiology is not a personal diagnosis from one shop-bought panel.
For athletes
In athletes, CRP helps separate “training sore” from systemic illness when used carefully. A spike with fever, swollen joints, or persistent fatigue deserves rest and medical advice, not another threshold session.
Ultra-endurance events and muscle-damaging blocks can raise CRP briefly. Overreaching and inadequate recovery sometimes travel with inflammatory signals, but CRP alone cannot diagnose overtraining syndrome. Pair with resting heart-rate trends, mood, sleep, and performance, and get urgent care for suspected infection that is not settling.
Related tests
Showing 6 of 7 panels that include C-reactive protein.
