C-Reactive Protein (CRP)

C-reactive protein (CRP) is one of the plasma protein found in the blood plasma, produced by the liver.

Gist

Acute-phase protein; inflammatory marker; Binds to damaged cells and amplifies immune response; Used to measure bodily stress and immune response.

Inflammation

Inflammation is your body’s response to irritants, pathogens and cell damage.

How does it get into your bloodstream

There are some steps before/during/after CRP gets into the bloodstream:

1. You get an infection or injured
2. Immune cells (macrophages/dendritic cells) detect threat (bacteria)
3. They release cytokines (chemical messenger molecule)
4. cytokines reach the liver through bloodstream
5. The liver ups CRP production
6. CRP levels in blood go up (biomarker)
7. CRP binds to damaged cells / bacteria
8. This marks them for destruction by complement and macrophages
9. Infection clears up, cytokine production stops
10. CRP levels drop (biomarker)

Acute vs Chronic inflammation

Acute inflammation can be caused by injuries or infections. Chronic inflammation, and therefore consistent higher CRP readings, can be an indicator for an underlying issue.

Timing

CRP is a great inflammatory marker because of its clockwork-like timing. So an infection’s levels would look something like this (not real CRP measurements):

• Hour 0 CRP 2 mg/L baseline; infection starts, cytokines begin
• Hour 6 CRP 5 mg/L first rise
• Hour 14 CRP 20 mg/L doubling every ~8h now
• Hour 24 CRP 60 mg/L clearly abnormal
• Hour 48 CRP 160 mg/L peak. antibiotics working, cytokines stop
• Hour 67 CRP 80 mg/L one half-life later. Halves every ~19h from here
• Hour 86 CRP 40 mg/L
• Hour 105 CRP 20 mg/L
• Hour 124 CRP 10 mg/L
• Day 7 CRP 3 mg/L back to baseline

Ref range

• < 5 mg/L - Normal
• 5-10 mg/L - Mild inflammation
• 10-50 mg/L - Moderate inflammation
• 50-100 mg/L - Significant inflammation (fighting off disease)

• 100 mg/L - Severe infection (count your days)