CRP optimal range and reference range
Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026
Sera's bands for CRP:
- Optimal 0 – 5 mg/L (0 – 0.5 mg/dL); out of range below 0 or above 5 mg/L.
Evidence grade: Published reference interval. A band that primarily reflects a published adult laboratory or population reference interval. It is not necessarily applicable to every assay or laboratory.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| mg/L | 0 – 5 | — | below 0 or above 5 |
| mg/dL | 0 – 0.5 | — | below 0 or above 0.5 |
No separate Sufficient band is currently defined for this marker.
What the evidence says
Standard CRP is a test for active inflammation or infection, not a cardiovascular risk figure. That is what hsCRP is for, and its cut-offs of 1 and 3 mg/L do not apply here. The band ends at 5 mg/L, the adult reference limit UK laboratories print. Labcorp prints 10 mg/L, so a result between 5 and 10 can be normal on a US report and is flagged here. Below 5 mg/L does not exclude low-grade inflammation, and many assays cannot measure that low, so a result reported as below 5 reads as in range. Results above 100 mg/L usually mean acute bacterial infection or active inflammatory disease. CRP rises within hours of infection or injury and falls over days, so repeat it once the person is well before reading anything into a mild rise.
Sources
- C-reactive protein (CRP) — University Hospitals Birmingham NHS Foundation Trust, Pathology, 2026 · Laboratory / reference-interval sourceAdult reference range 0 to 5 mg/L on the Abbott assay. Up to 5 mg/L excludes many acute inflammatory diseases but not all inflammation, and above 100 mg/L suggests acute bacterial infection or active inflammation. Updated August 2026.
- CRP (C-reactive protein) — Gloucestershire Hospitals NHS Foundation Trust, Pathology, 2026 · Laboratory / reference-interval sourceAdult reference range below 5 mg/L. Reviewed January 2026. A second NHS laboratory on the same edge.
- C-Reactive Protein (CRP), Quantitative (test 006627) — Labcorp test directory, 2026 · Laboratory / reference-interval sourceAdult (over 17) interval 0 to 10 mg/L for both sexes. The page points to the separate high-sensitivity assay for cardiac risk. This is the 10 mg/L edge US reports print.
- ABIM Laboratory Test Reference Ranges, January 2026 — American Board of Internal Medicine, 2026 · Laboratory / reference-interval sourceUS reference table: standard C-reactive protein 0.8 mg/dL or less (8 mg/L), listed separately from high-sensitivity CRP, which carries the cardiovascular risk categories (below 1, 1 to 3, above 3 mg/L).
What CRP (C-Reactive Protein, standard) measures
The standard C-reactive protein test, which rises within hours of infection, injury or active inflammation.
A test for active inflammation or infection, not a cardiovascular risk figure. Its lower reporting limit (often below 4 or 5 mg/L) is too coarse for the 1 and 3 mg/L risk tiers, which belong to the high-sensitivity test.