CRP is an acute-phase protein that the liver releases into the blood in response to inflammation. It is the fastest and most universal marker: it reacts within a few hours and rises with infection, injury and autoimmune processes.
Two tests should be distinguished. Ordinary CRP looks for overt inflammation (normal below 5 mg/L). High-sensitivity (hs-CRP) measures the same molecules but more precisely — and is needed to assess chronic low-grade inflammation, which is linked to cardiovascular risk and aging.
Reference ranges
Two different tests — two different sets of thresholds:
| Ordinary CRP — normal | below 5 mg/L |
| hs-CRP — low CVD risk | below 1 mg/L |
| hs-CRP — moderate risk | 1 – 3 mg/L |
| hs-CRP — high risk | above 3 mg/L |
| Overt inflammation / infection | above 10 mg/L |
What an elevated level means
A sharply elevated CRP (tens and hundreds of mg/L) means acute inflammation: a bacterial infection, a flare of autoimmune disease, injury, the postoperative period.
A moderately elevated hs-CRP (1–3 and especially above 3 mg/L) in the absence of infection is a sign of chronic low-grade inflammation. It is linked to visceral obesity, insulin resistance, smoking, periodontitis, chronic stress and lack of sleep. This "silent" inflammation is considered one of the mechanisms of accelerated aging (inflammaging) and is included in biological-age models.
What a low level means
A low CRP is a favorable sign: there is no active inflammation.
An hs-CRP value below 1 mg/L corresponds to low cardiovascular risk. There are no risks of a "too low" CRP.
How the test is done
Venous blood. Strict fasting is not required, but it is better to test fasting and in the morning.
Critically important: do not test during or right after an acute illness, injury, surgery or intense exercise — inflammation will raise CRP and make chronic-risk assessment meaningless. For hs-CRP the right approach is to test twice, 2 weeks apart, during a calm period and take the average.
What affects the value
- Any infection and injury — raise it sharply (this is normal).
- Visceral obesity — fat tissue itself releases pro-inflammatory substances.
- Smoking — sustains chronic inflammation.
- Chronic stress and lack of sleep — raise hs-CRP.
- Gum disease (periodontitis) — a common and unnoticed cause of chronic inflammation.
- Physical activity and weight loss — lower hs-CRP.
Calculate using this marker
Calculators where C-reactive protein is used directly:
Frequently asked questions
How does hs-CRP differ from ordinary CRP?
It is the same protein but tests of different precision. Ordinary CRP looks for overt inflammation (threshold 5 mg/L). The high-sensitivity test measures low concentrations and is needed to catch chronic low-grade inflammation — there even 1–3 mg/L matters.
My CRP is high but I'm not ill — why?
First rule out the non-obvious: a recent cold, intense exercise, injury, gum problems. If there is no infection, a moderately elevated hs-CRP most often reflects chronic inflammation against a background of visceral obesity, smoking, lack of sleep or insulin resistance.
How do you lower hs-CRP?
The same measures work as against visceral fat: weight loss, regular aerobic exercise, quitting smoking, normalizing sleep and treating chronic infection foci (primarily the gums). There is no separate "anti-inflammation pill" here.