CRP tests – what are they?



What does CRP measure?

Chemical messengers (cytokines)are released during the innate immune response. The cytokines known as IL-6 (InterLeukin-6) and TNF (Tumour Necrosis Factor) stimulate the liver to produce the protein known as CRP (C-reactive protein).  CRP is a non specific measure of inflammation. It doesn’t tell you what is inflamed. It doesn’t give you a diagnosis.

CRP mg/dL CRP mg/ml Inflammatory State
> 1 mg/dL > 10 mg/ml Inflammation such as infection or flare. Often with heat/redness/pain
>0.3-1.0 mg/dL > 3-10 mg/ml inflammation (meta-inflammation). insulin resistance, sleep apnea, obesity, hypertension, sedentary lifestyle
>0.2 mg/dL > 2 mg/L increases the chance of a cardiovascular event


A CRP rise is dependent on which cytokines are released. Patients with lupus produce different cytokines so the CRP often does not reflect the activity of the disease.  Some RA sufferers can have inflammation with a normal CRP. These people are releasing different cytokines. One study has shown that up to 25% of sufferers of RA had marked inflammation with a normal CRP.  In summary, if your CRP was high at diagnosis, it is one way of tracking your response to your immune modulating actions.

My summary is taken from UpToDate a subscription medical review service. (You can purchase a short-term membership)

The review was written by I Kusher, MD. Literature review was done last in Oct 2021. The review was updated July 2021. The study pointing out the not all inflammatory RA sufferers have elevated CRP or ESR is reference #87: Kay J, Morgacheva O, Messing SP, et al. Clinical disease activity and acute phase reactant levels are discordant among patients with active rheumatoid arthritis: acute phase reactant levels contribute separately to predicting outcome at one year. Arthritis Res Ther 2014; 16:R4

By Dr. Charmaine Jones, see Patient Advisory Bio Click here