In short
- CRP is a protein your liver produces as soon as the immune system goes into action.
- A raised value shows that inflammation is present, but not where or why.
- hsCRP is the same substance, measured with a more sensitive method for low-grade inflammation.
- An infection, injury or heavy training session in the preceding days colours the result.
What CRP is and why it moves
CRP stands for C-reactive protein, a protein your liver produces as soon as the immune system raises the alarm. With an infection, tissue damage or an inflammatory reaction, immune cells release signalling substances, and the liver responds by releasing CRP into the blood.
The protein then helps clear away bacteria and damaged cells. So CRP is not a disease and not a cause, but a response: a signal that your body is dealing with something.
What makes CRP so useful is its speed. The value starts rising within a few hours of an inflammatory reaction beginning and peaks within a day or two. Once the trigger disappears, CRP falls back just as briskly.
That rapid rise and fall makes the value suitable for following a course, for example whether an infection is genuinely settling. That same mobility also means a single measurement is always a snapshot.
Acute inflammation: a fast gauge
In an acute situation CRP does what it is good at. These situations usually produce a clearly raised value:
- Pneumonia
- A urinary infection that has spread upwards
- An infected wound
- Surgery
- A substantial injury
In that context doctors mainly use CRP to judge how pronounced the response is and whether treatment is working.
One important nuance applies: CRP alone cannot say with certainty whether an infection is caused by a bacterium or a virus. It helps with that judgement, together with your complaints, your temperature and the physical examination, but it does not decide on its own.
Low-grade inflammation and hsCRP
Besides the acute variety there is low-grade inflammation: mild, ongoing immune activity without you feeling ill. That form is linked to:
- Excess weight and abdominal fat in particular
- Smoking
- Chronic lack of sleep
- Little exercise
- Prolonged stress
- Insulin resistance
Seeing those small differences reliably requires a more sensitive measuring technique, called hsCRP, where hs stands for high sensitivity. So it is not a different protein, but the same substance measured with a finer method.
It is precisely this low-grade inflammation that is interesting for cardiovascular risk. Inflammation plays a part in the formation and destabilising of plaques in the vessel wall, which is why hsCRP is used in risk assessment as an addition to cholesterol, ApoB, blood pressure, blood sugar and smoking.
Addition is the key word here. An hsCRP value replaces none of those other factors and is no prediction in itself. It is an extra piece of the puzzle that can weigh in when your doctor is unsure how firmly to judge your risk.
| Acute inflammation | Low-grade inflammation | |
|---|---|---|
| What it is | A clear response to infection, injury or surgery | Mild, ongoing activity of the immune system |
| How you feel | You feel ill or have a clear complaint | You usually do not feel ill |
| Test | Ordinary CRP | hsCRP, the same substance with a more sensitive method |
| Used for | Detecting inflammation and following its course | An addition when judging cardiovascular risk |
What CRP does not tell you
This is the most important limitation to know. CRP does not point to a place. A raised value does not say whether the inflammation is in your lungs, your bowels, your teeth, a joint or a wound. It says nothing about the cause either: an infection, a rheumatic condition, bowel inflammation and a broken bone can all four produce a similar rise.
Conversely, a CRP that is not raised does not rule a problem out. Some conditions run with little or no CRP response, and at an early stage the value can still lag behind.
CRP is also not cancer screening and not a general health score. It is a signpost showing that something is going on, after which further looking is needed.
Have CRP measured at Bloodworks
CRP as an individual test, including doctor interpretation and a personal PDF report. The price is all-in, so the blood draw fee is included. No referral required, results typically within 2 working days.
What can distort the result
CRP responds to far more than illness alone, which makes the timing of your blood draw important. These things can lift the value temporarily:
- A cold or mild flu in the preceding days
- Inflamed gums
- Recent surgery or dental work
- A sprained ankle
- A marathon or a heavy strength session
Muscle damage after intensive exercise is a common and entirely harmless explanation. Pregnancy, the use of oestrogen-containing contraception and excess weight also go together with a higher value on average. In the other direction, anti-inflammatory medicines such as prednisolone or NSAIDs can push the value down.
If you want a clean picture of your baseline, plan the draw at a settled moment: not shortly after an infection or period of illness, and not in the days following an exhausting workout.
When is testing worthwhile?
CRP is mainly useful in combination, not as a stand-alone number. With persistent complaints without a clear explanation, such as long-standing fatigue, unexplained fever, joint complaints or unintended weight loss, CRP helps to see whether an inflammatory component is involved.
A broader picture then makes sense, including your blood count and the sedimentation rate. The Immunity & Inflammation package bundles those values in a single draw for €109, excluding the €29 blood draw fee, which is waived from €225.
A second good reason is following a course: a repeat test after a few weeks shows whether a raised value is genuinely coming down. And when mapping your cardiovascular risk, hsCRP can be an additional piece of the puzzle alongside your cholesterol profile.
When a blood test is not the answer
If you genuinely feel ill right now, with persistent fever, breathlessness, severe pain, confusion or a rapidly worsening condition, do not order a blood test and do not sit waiting for a result. Contact your GP or the out-of-hours service. In an acute situation, assessment by a doctor, with examination and the right tests at the right moment, is what you need.
Conversely, a normal CRP is not a free pass. If your complaints persist while your value shows nothing unusual, have that investigated rather than reading it as reassurance.
Frequently asked questions
What is the difference between CRP and hsCRP?
It is the same protein. With hsCRP a more sensitive measuring method is used, which makes small differences at the low end visible. Ordinary CRP is meant for detecting and following clear inflammation, hsCRP mainly for judging low-grade inflammation in cardiovascular risk.
Can exercise influence my CRP value?
Yes. Intensive exertion causes mild muscle damage, and CRP responds to that. After a marathon, a heavy strength session or an unusually long endurance effort, the value can be raised for a few days without anything being wrong. So ideally plan your blood draw on a quiet day.
Do I need to fast for a CRP test?
No, fasting is not necessary for CRP. If values that do require fasting are measured in the same draw, such as glucose or triglycerides, a fasting sample may still be requested. Follow the instruction you receive with your appointment.
Does a raised CRP mean I have a serious illness?
Not automatically. By far the most rises are caused by an ordinary infection, inflammation in the mouth or gums, an injury or a recent procedure. If the value stays raised without a clear explanation, further investigation by your GP is appropriate.
Do I need a referral for a CRP test?
No. At Bloodworks you have CRP tested without a referral, at one of the more than 750 affiliated collection points in the Netherlands. Your result is reviewed by a doctor and you receive a personal PDF report, typically within 2 working days.