Short answer: CRP (C-reactive protein) is a protein the liver makes quickly when there is inflammation or infection; it rises within hours and falls within days. ESR (erythrocyte sedimentation rate, sed rate) measures how fast red cells settle in a tube; it rises more slowly and stays up longer. Neither says where the inflammation is or what causes it: they show that something is going on and help follow it.
At a glance
| CRP | A protein the liver makes within hours of inflammation; falls within days |
|---|---|
| ESR | How fast red cells settle in a tube; rises slowly, stays up longer |
| Units | mg/L (CRP); mm/h (ESR) |
| LOINC | 1988-5 (CRP), 30341-2 (ESR) |
| What they do not say | Where the inflammation is or what causes it |
| Keep | The series with the date and what was happening |
What the test measures
CRP is measured directly in the blood. A high-sensitivity CRP (hs-CRP) test measures very low levels and is used for a different purpose, as one factor in cardiovascular risk; the method is printed on the report.
ESR is a physical measurement in millimetres per hour. It is affected by age, sex, anaemia and pregnancy, which is why it is less specific than CRP.
When it is ordered
Common reasons, which your doctor adapts to you:
- when a doctor looks for or follows an infection or inflammation;
- to monitor some inflammatory conditions and their treatment;
- hs-CRP: sometimes as part of a cardiovascular risk assessment.
How the result is written on the report
| Result on the report | LOINC code | Usual unit | Also seen as |
|---|---|---|---|
| C-reactive protein (CRP) | 1988-5 | mg/L | mg/dL (÷10) |
| ESR | 30341-2 | mm/h | — |
| ESR, Westergren method | 4537-7 | mm/h | — |
CRP is written in mg/L in most of Europe and in mg/dL in some US labs: mg/L = mg/dL × 10, so 0.5 mg/dL and 5 mg/L are the same value. This tenfold difference is the most common reading mistake with CRP.
Reading your report
A mild rise can follow a cold, an injury or intense exercise; a single value is read with symptoms and examination. CRP is useful to follow a known problem: a falling CRP over days usually goes with improvement, which is why keeping several results in one place helps. ESR changes slowly, so it is compared over weeks rather than days.
Keeping the results in your record
Scan or photograph the report in Anpheros Daily: each value is read with its unit and the laboratory's reference range, you check it, and it is stored with its LOINC code as an HL7 FHIR Observation, a format used by many hospitals and national health systems. Results from different laboratories line up on one chart over time, and the lab unit converter helps when two reports use different units. Our guide on how to read lab results explains reference ranges and flags in general; the lab results guide for a new doctor shows how to share them.
What this page does not do
It explains what the test is and how the result is written. It does not interpret your result, diagnose or recommend treatment: the meaning of a value depends on your history, your other results and how the sample was taken, and that is your doctor's job.
Related pages
Sources
Frequently asked questions
What is the difference between CRP and ESR?
CRP is a protein measured directly and changes within hours; ESR is how fast red cells settle and changes over days to weeks.
Is CRP in mg/L the same as in mg/dL?
No. mg/L is ten times the mg/dL number: 0.5 mg/dL equals 5 mg/L.
What is hs-CRP?
A high-sensitivity version of the CRP test that measures very low levels, used as one factor in assessing cardiovascular risk.
Does a high CRP mean an infection?
Not necessarily. It shows inflammation, which has many causes. Your doctor reads it with your symptoms and other results.
Try it in Anpheros Daily
Photograph your lab report and Anpheros Daily lines up each value with its reference range, so you can compare reports from different laboratories.
How it works in the app →
Anpheros builds a medical record that the patient controls and can share with any clinic, on an HL7 FHIR R4 platform, based in the EU. These guides help you understand and organise your health; they do not replace your doctor.
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