What does it mean when your doctor tells you that you have a high CRP?  The answer is both simple and yet complex.  Simply put, an elevated CRP means that something inside your body is causing inflammation.  A CRP, also known as a C-reactive protein, is one many proteins found in the blood referred to as acute phase reactants (APR).

Acute phase reactants

The name is slightly misleading as APRs increase both with acute and chronic inflammation. Acute phase reactants are proteins that increase or decrease by at least 25% during inflammation.  That being said, you can have positive or negative APR.  CRP is a positive APR, whereas albumin is a negative APR as it tends to decrease with inflammation.  It’s also important to note that APR changes are terribly non-specific, occurring in a multiple of situations:

• Infection
• Trauma
• Clots
• Systemic autoimmune diseases
• Cancer

Basically, anything that can cause inflammation or tissue injury can affect acute phase reactants.

Inflammation

Think of inflammation as a highly complex orchestra.  You have your wind instruments, brass, strings, percussion, etc. Together in perfect unison, they can produce a variety of music: melancholic, invigorating, soothing, frantic, etc.  Now instead of musical instruments think of inflammation as an orchestra of cell types and molecules initiating, amplifying, attenuating, and abolishing inflammation.

Chronic inflammation often cause the following symptoms:

• Fever
• Anemia
• Weight loss
• Fatigue
• Muscle loss
• Swollen lymph nodes

What does CRP do?

CRP has both proinflammatory and anti-inflammatory effects.  It helps recognize and eliminate pathogens and helps clear necrotic tissue and apoptotic cells (i.e., cells that self-destructed).  These actions help reduce inflammation.

However, CRP can increase inflammation by activating the complement system and by forcing cells to release inflammatory cytokines.  These actions can actually worsen tissue injury depending on the situation.

How is CRP used in a clinical situation?

Broadly speaking, CRP and acute phase reactants in general detect the presence and intensity of an inflammatory process.  They do not help us decide what exactly is causing the inflammation, simply that it is there.

There are certain exceptions.  For example, an APR called procalcitonin sometimes helps us differentiate infection from autoimmune inflammation or that caused by cancer.

What is a normal CRP level?

We actually don’t really know was normal or clinically benign CRP is.  Instead we refer to inflammation as low, moderate, or high-grade inflammation.

What is low-grade inflammation and what causes it?

Low-grade inflammation refers to a situation resulting in a CRP between 0.3 and 1 mg/dL.  The following are some situations that can cause low-grade inflammation.

• Atherosclerosis
• Obesity
• Sleep apnea
• Diabetes mellitus
• High blood pressure
• General poor health
• Sedentary lifestyle
• Unhealthy diets
• Social isolation
• Stress!!!

Moderate to marked elevation of CRP

These are CRP levels that are greater than 1 mg/dL.  What is “moderate” and what is “marked” is a matter up for debate.  It really depends on the clinician. Essentially, the higher the level the more inflammatory the situation.

Why does my doctor get a CRP and an ESR?

An erythrocyte sedimentation rate (ESR) or sed rate is another way of measuring inflammation, although in this situation indirectly so.  An ESR measures the rate at which red blood cells suspended in plasma settle when place in a vertical tube.  Systemic inflammation increases the ESR, but other situations that are not related to inflammation can also influence the level.

Increased ESR

• Increased age
• Female sex
• Anemia
• Kidney disease
• Obesity (fat cells secrete interleukin-6)
• Technical problems (tilting the tube or performing the test in high room temperature)

Decreased ESR

• Have abnormal red blood cells (e.g., sickle-cell anemia, polycythemia)
• High white blood count (WBC)
• Heart failure
• Having low levels of fibrinogen
• Technical problems (e.g., low room temperature, short ESR tube)

We often get a CRP and an ESR because oftentimes there is a bit of discrepancy between these levels.

Discrepancies between acute phase reactants

This happens actually happens quite frequently.  As previously discussed many situations can alter the result of the ESR and to a certain degree also the CRP.  These in and of itself, can influence the discrepancy.

Moreover, ESR level change relatively slowly, whereas CRP levels tend to change rapidly.  For example, if someone is experiencing a rheumatoid arthritis flare-up, I usually will prescribe prednisone to decrease the inflammation.  Before the prednisone both the ESR and CRP will be high.  If I were to repeat the test in 3 days, the ESR will most likely still be elevated but the CRP may be low.

There are also some diseases where the discrepancy exists and can help differentiate it from other rheumatic diseases.  For example, in macrophage activation syndrome the ESR is famously low and the CRP is strikingly raised.

Summary

A CRP is a type of acute phase reactant seen in both acute and chronic inflammation.  Elevations occur in a variety of situations including but not limited to infection, autoimmune conditions, trauma, and malignancy.  Rheumatologist often order acute phase reactants to help monitor disease activity.  But labs are not perfect.  Oftentimes, a rheumatologist will order many acute phase reactants.

References

UpToDate

Medical Disclaimer

This information is offered to educate the general public. The information posted on this website does not replace professional medical advice, but for general information purposes only. There is no Doctor – Patient relationship established. We strongly advised you to speak with your medical professional if you have questions concerning your symptoms, diagnosis and treatment.