CRP Unit Converter
CRP Unit Converter
Convert C-reactive protein between mg/L, mg/dL and µg/mL, and see why the tenfold difference between the two mass units is the trap that matters.
CRP converter
mg/L ⇄ mg/dLCRP 8 mg/L
Formula and conversion factors
mg/L = mg/dL × 10
µg/mL = mg/L (numerically identical)
- × 0.1
- one decilitre is 100 mL, so a concentration per decilitre is a tenth of the same concentration per litre — 5 mg/dL is 50 mg/L
- µg/mL
- numerically identical to mg/L; no conversion is needed between them
- no molar unit
- CRP is a pentameric protein reported by mass only; molar reporting is not used clinically and none is offered here
- hs-CRP
- not a different molecule — the same protein measured with an assay sensitive enough to discriminate within the 0–10 mg/L range for cardiovascular risk
Worked example
CRP 8 mg/L
8 × 0.1 = 0.80 mg/dL
= 8.0 µg/mL
Above the adult reference interval of 0–5 mg/L
Thresholds in both conventions
| mg/L | mg/dL | |
|---|---|---|
| Adult reference interval | < 5 | < 0.5 |
| hs-CRP, lower cardiovascular risk | < 1 | < 0.1 |
| hs-CRP, higher cardiovascular risk | > 3 | > 0.3 |
| Mild elevation — viral illness, low-grade inflammation | 5 – 40 | 0.5 – 4.0 |
| Marked elevation — bacterial infection more likely | > 100 | > 10 |
CRP against ESR for following a patient
| CRP | ESR | |
|---|---|---|
| Starts to rise | 4 – 6 hours | 24 – 48 hours |
| Peak | About 48 hours | Days |
| Half-life / fall | About 19 hours | Days to weeks |
| Affected by anaemia, paraproteins, age | No | Yes |
Reading a CRP: units first, then kinetics
C-reactive protein is reported in mg/L in most of the world and in mg/dL in parts of the United States, and the two differ by a factor of ten. That difference is the most consequential trap on this page: a CRP of 5 mg/dL is 50 mg/L, a marked elevation that would usually prompt a search for bacterial infection, while 5 mg/L sits at the top of the normal adult range and needs no action at all. When a result arrives without its unit attached, resolve the unit before interpreting the number.
µg/mL is numerically identical to mg/L, so no arithmetic is needed between them; it appears mainly on research assays and some immunology reports. High-sensitivity CRP is a further source of confusion. It is not a different molecule and not a different analyte — it is the same protein measured with an assay sensitive enough to discriminate within the 0 to 10 mg/L range, where cardiovascular risk stratification operates. A standard assay cannot resolve differences that small, which is why the two reports coexist.
The kinetics are what make CRP more useful than the ESR for following a patient. It begins to rise within four to six hours of the inflammatory stimulus, peaks at around 48 hours, and falls with a half-life of about 19 hours once the stimulus stops. That short half-life means the level reflects the current state of the illness rather than the previous week’s, so a falling CRP on serial measurement is genuine evidence of response. The ESR, by contrast, changes over days to weeks and is shifted by anaemia, age and paraproteins.
A normal CRP does not exclude active disease. It rises unreliably in some conditions — most notably in systemic lupus erythematosus, where a flare without serositis often produces little or no rise, which is part of why a high CRP in a lupus patient should raise the question of infection rather than flare. It is also blunted in liver failure, since it is synthesised hepatically, and by IL-6 receptor blockade with tocilizumab, which can leave CRP normal in the face of serious infection.
Frequently asked questions
How do I convert CRP from mg/dL to mg/L?
Multiply by ten. A CRP of 0.8 mg/dL is 8 mg/L. Going the other way, divide the mg/L figure by ten.
Is µg/mL the same as mg/L for CRP?
Yes, they are numerically identical. One microgram per millilitre is one milligram per litre, so no conversion is needed.
Is high-sensitivity CRP a different test?
It measures the same protein, using an assay sensitive enough to discriminate between values in the 0 to 10 mg/L range. That range is where cardiovascular risk stratification operates, and a standard CRP assay cannot resolve it. The molecule and its units are unchanged.
Why is CRP more useful than ESR for tracking treatment response?
CRP rises within hours and falls with a half-life of about 19 hours once the stimulus stops, so it tracks the current state of the illness. The ESR changes over days to weeks and is also affected by anaemia, age and paraproteins.
Can a patient have active disease with a normal CRP?
Yes. Lupus flares without serositis often produce little or no rise, and CRP is blunted in liver failure and by IL-6 receptor blockade with tocilizumab. A normal result never excludes active disease on its own.
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References
- Pepys MB, Hirschfield GM. C-reactive protein: a critical update. J Clin Invest. 2003;111(12):1805–1812.
- Ridker PM, Danielson E, Fonseca FAH, et al. Rosuvastatin to prevent vascular events in men and women with elevated C-reactive protein. N Engl J Med. 2008;359(21):2195–2207.
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory. CLSI guideline EP28-A3c.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.