Ferritin, inflammation and CRP: tested together

Ferritin is a store of iron, but it is also affected by inflammation. That is one of the main reasons a ferritin number cannot always be taken at face value, and why a doctor may look at other tests alongside it.

What CRP is

C-reactive protein (CRP) is a protein the liver makes in response to inflammation. A CRP test measures how much of it is in the blood. MedlinePlus is clear about what it cannot do: it shows that inflammation may be present, but not what is causing it or where it is.

Why CRP and ferritin appear together

MedlinePlus says ferritin can be raised by inflammation, including infection and recovery from surgery, as well as by some autoimmune conditions and liver disease. A CRP result gives a doctor an additional piece of information to consider when reading a ferritin result. Whether it changes the reading in any individual case is something for the doctor to say.

There are two kinds of CRP test

A standard CRP test is used for infections and inflammatory conditions. A high-sensitivity CRP (hs-CRP) test detects very small increases and is used for a different purpose, estimating heart disease risk. Check which test you had.

Check the unit

CRP is printed as mg/L on most reports and as mg/dL on some. One mg/dL is ten mg/L, so the digits can differ by a factor of ten for the same quantity. Always write the unit with the number, and use a unit converter (free at ferrolady.com/tools) if you need to compare two reports.

MedlinePlus also says some medicines, including anti-inflammatory painkillers such as ibuprofen and aspirin, and some supplements, can affect CRP, so tell the person ordering the test what you take.