CRP and ESR — the two common inflammation markers explained, including why GPs order them and how they are reported in Australia.
CRP (C-reactive protein) is a protein made by the liver. Its level in the blood rises when there is inflammation somewhere in the body — for example from infection, injury, or an inflammatory condition.
CRP is a general marker. A raised level tells your GP that inflammation is present, but not where it is or what is causing it. It is interpreted alongside your symptoms and other findings.
In Australia, CRP is reported in mg/L. A separate, more sensitive version called high-sensitivity CRP (hsCRP) is sometimes used in cardiovascular risk assessment.
ESR (erythrocyte sedimentation rate) is an older inflammation marker that measures how quickly red blood cells settle in a tube. Like CRP, it rises with inflammation, but it changes more slowly — taking longer to rise and longer to settle back down.
Because they behave differently over time, a GP may order CRP, ESR, or both depending on what they are looking into.
Your GP chooses these tests based on your individual situation.
CRP is reported in mg/L and ESR in mm/hr. As a commonly used guide, a low CRP is typical in the absence of significant inflammation; ESR reference points are age- and sex-dependent, so the "normal" figure differs from person to person.
Reference intervals vary between laboratories. Always read the reference range printed on your own report, and only the clinician who ordered the test can interpret what your result means for you.
No. CRP shows that inflammation is present but not where it is or what is causing it. It is one piece of information your GP considers alongside your symptoms and other tests.
No. Neither CRP nor ESR requires fasting. Both are standard blood tests.
High-sensitivity CRP (hsCRP) measures very low CRP levels more precisely and is sometimes used as part of cardiovascular risk assessment. It is a different request from a standard CRP.