Half-Life of C-Reactive Protein
The half-life of C-reactive protein (CRP) is approximately 19 hours, though clinically relevant elimination occurs over 46-48 hours in most patients.
Kinetic Properties
The biological half-life of CRP has been measured in clinical studies:
In patients with community-acquired pneumonia, the biological half-life of CRP was 46.4 ± 21.7 hours when measured during successful treatment and recovery 1
CRP synthesis begins 4-6 hours after an inflammatory insult, with concentrations doubling every 8 hours and reaching peak levels at 36-50 hours 2, 3
Plasma CRP levels start to rise 12-24 hours after an acute inflammatory or infectious insult, reaching maximum values after 48 hours 2
Clinical Implications of CRP Kinetics
The relatively long half-life of CRP compared to other inflammatory markers has important clinical applications:
CRP remains elevated longer than acute phase reactants with shorter half-lives, making it useful for monitoring chronic inflammatory conditions rather than rapid changes in acute infection 4
Serum CRP levels can change 10-100 fold within 6-72 hours of any tissue damaging event, with the rate of change determined by synthesis rather than elimination 5
CRP production and elimination are not influenced by renal replacement therapy or immunosuppression (including systemic steroids and neutropenia), making it a reliable marker across diverse patient populations 2, 3
Comparison to Other Biomarkers
Understanding CRP's half-life relative to other inflammatory markers helps guide appropriate clinical use:
Procalcitonin (PCT) has a much shorter half-life of 22-35 hours, making it more responsive to acute changes in infection status 2
Serum amyloid A (SAA) has a biological half-life of 34.9 ± 28.7 hours, significantly shorter than CRP's 46.4 hours (p = 0.0014) 1
Fibrinogen (for which ESR is an indirect measure) has a much longer half-life than CRP, making ESR more suitable for monitoring chronic conditions while CRP is preferred for acute inflammatory diagnosis and treatment monitoring 4
Important Clinical Caveats
The sole determinant of CRP plasma levels is its synthesis rate, which is proportional to the intensity of the inflammatory insult—not its elimination rate 2, 3
CRP levels decrease rapidly after antibiotic treatment or resolution of inflammation, with the decline following an exponential pattern 1
Normal baseline CRP levels are typically below 3-5 mg/L in healthy individuals, though levels can rise above 500 mg/L during acute illness 3