CRP vs ESR: Key Differences
| Feature | CRP | ESR |
|---|---|---|
| What it measures | Liver-produced acute phase protein | Rate red cells settle in 1 hour |
| Rise time | 6–8 hours after trigger | 24–48 hours after trigger |
| Fall after resolution | Falls quickly (half-life 19 hours) | Falls slowly over days-weeks |
| Normal range | <5 mg/L | Men: age/2; Women: (age+10)/2 mm/hr |
| More useful for | Monitoring infection/inflammation acutely | PMR, GCA, myeloma, chronic disease |
| Affected by anaemia/pregnancy | No | Yes — falsely elevated |
Interpreting CRP Levels
| CRP Level | Likely Cause |
|---|---|
| <5 mg/L | Normal — no significant inflammation |
| 5–50 mg/L | Mild-moderate inflammation: viral infection, mild bacterial, flare of autoimmune |
| 50–150 mg/L | Moderate-severe: pneumonia, UTI, autoimmune flare, post-surgical |
| >150 mg/L | Severe: serious bacterial infection, sepsis, major trauma |
| >350 mg/L | Often indicates bacterial sepsis or severe tissue damage |
High-Sensitivity CRP (hsCRP)Standard CRP measures inflammation. High-sensitivity CRP (hsCRP) can detect very low-level chronic inflammation and is used as a cardiovascular risk marker. Persistently elevated hsCRP (>3 mg/L) predicts future heart attack and stroke risk.
Can a normal CRP rule out infection?
A very low CRP (<5 mg/L) makes significant bacterial infection less likely, but does not exclude it early (within 6 hours). ESR and white cell count add information. Clinical assessment remains essential.
Why is my CRP raised with no obvious cause?
Mild chronic CRP elevation (5–20 mg/L) can be caused by obesity, metabolic syndrome, chronic dental disease, sleep apnoea, depression, or subclinical inflammation. Persist with investigation if no clear cause.
What is the difference between CRP and hs-CRP?
They measure the same molecule but at different sensitivities. Standard CRP is for diagnosing acute inflammation (>5 mg/L threshold). hsCRP measures very low levels (<1 mg/L) for cardiovascular risk prediction.
In PMR, what does a very high ESR mean?
Polymyalgia rheumatica (PMR) typically causes a dramatically elevated ESR (often >50–100 mm/hr) with elevated CRP and clinical symptoms. ESR >50 in the right clinical context is highly supportive of PMR.
Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.