Key inflammation markers compared
| Marker | Normal | Rises within | Best for |
|---|---|---|---|
| CRP (C-reactive protein) | <10 mg/L | 4–8 hours | Acute infection, monitoring treatment response |
| ESR (erythrocyte sedimentation rate) | Men: <15; Women: <20 mm/hr | 24–48 hours | Chronic inflammation, temporal arteritis, myeloma |
| High-sensitivity CRP (hsCRP) | <1.0 mg/L (cardiovascular risk) | 4–8 hours | Cardiovascular risk assessment |
| Procalcitonin (PCT) | <0.25 ng/mL | 2–6 hours | Bacterial infection (vs viral); sepsis severity |
| Ferritin | 20–200 ng/mL | Hours to days | Iron stores; extreme rise in haemophagocytic syndrome, Still's disease |
| Fibrinogen | 200–400 mg/dL | Hours | Acute phase reactant; clotting; cardiovascular risk |
CRP vs ESR — which is better?
Different tools for different questions
CRP rises and falls quickly — it's the best marker for monitoring acute infection and treatment response. If CRP falls with antibiotics, the infection is responding. ESR rises more slowly (peaks at 24–48 hours) and falls slowly — it's better for monitoring chronic conditions like rheumatoid arthritis, temporal arteritis, and multiple myeloma. A very high ESR (>100 mm/hr) is characteristic of temporal arteritis, myeloma, severe bacterial infection, and nephrotic syndrome.
What does a very high CRP mean?
| CRP level | Likely cause |
|---|---|
| <10 mg/L | Normal — no significant inflammation |
| 10–50 mg/L | Mild inflammation — viral infection, minor bacterial infection, RA flare |
| 50–200 mg/L | Significant inflammation — active bacterial infection, serious flare |
| >200 mg/L | Severe bacterial infection, sepsis, severe burn, major trauma |
Procalcitonin — the bacterial infection marker
Procalcitonin (PCT) is produced by the body specifically in response to bacterial infection — not viral infections. This makes it useful for distinguishing bacterial pneumonia (high PCT) from viral pneumonia (low/normal PCT), and for deciding whether antibiotics are needed. Rising PCT indicates worsening infection; falling PCT with treatment indicates improvement. PCT is also used to guide antibiotic duration — antibiotics can often be safely stopped when PCT falls below 0.25 ng/mL.
Questions to ask your doctor
- Is my CRP raised — does this suggest active infection or inflammation?
- Is my ESR elevated — could this be temporal arteritis or myeloma?
- Has my procalcitonin been checked to guide antibiotic use?
- Is my inflammation responding to treatment (CRP trending down)?