Patient Guide

Understanding Inflammation Blood Tests

Name: Understanding Inflammation Blood Tests: CRP, ESR & More
Creator: Suman Konda
Published: 2026-07-05

When your body fights infection or has an autoimmune flare, it releases inflammatory proteins into the blood. These markers help doctors detect and monitor inflammation.

Written by Suman Konda, PharmD, Clinical Pharmacist · Editorial policy · Not medical advice

Last updated: 01 August 2026 · How we check our content

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	Men: 24–336 ng/mL; Women: 11–307 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)?