What Infections Can Cause High CRP Levels

How Infections Cause High CRP Levels

When your body senses an infection, like bacteria or a virus, your immune system quickly reacts. One of the first things it does is tell your liver to make more C-reactive protein. This is part of your body’s early defense system.

Your white blood cells release a chemical called interleukin-6 (IL-6) when there’s a problem. IL-6 travels to your liver and tells it to start producing CRP.

CRP then moves into your bloodstream and helps your immune system fight off the infection.

This whole process is known as an acute-phase response, and CRP is one of the first markers to rise.

How Quickly CRP Levels Rise and Fall

CRP levels don’t stay the same for long. They can:

• Start rising within 6-8 hours after an infection begins
• Reach their peak in 2-3 days
• Drop quickly once the infection is under control

That’s why doctors often repeat the CRP test, to see if your treatment is working or if the infection is getting worse.

What Infections Can Cause High CRP?

CRP levels often rise when your body is fighting an infection. But the type of infection affects how high they go. Let’s break it down into different categories.

Bacterial Infections That Raise CRP the Most

Pneumonia is a lung infection that can cause a big spike in CRP levels. You may have:

• Cough with mucus
• Fever or chills
• Trouble breathing

CRP often rises above 50 mg/L in serious cases.

UTIs affect the bladder or kidneys and are common. A high CRP level may suggest the infection is moving beyond the bladder, especially if you also have:

• Back pain
• Fever
• Pain during urination

Sepsis is a life-threatening condition caused by an overwhelming infection. CRP levels in sepsis can go very high, often over 100 mg/L.

It’s the body’s way of screaming for help.

This skin infection can make your skin red, swollen, and warm. If the infection spreads deeper, CRP levels go up.

It's especially common on the legs.

Osteomyelitis is an infection in the bone. CRP helps doctors track how serious it is.

People with bone infections often have long-lasting high CRP levels that take time to come down.

Viral Infections

COVID-19 is caused by a virus that affects the lungs and immune system. In many people, CRP levels can rise early in the illness, even before breathing problems start.

Higher CRP levels are often linked with more serious cases, especially if the infection spreads to the lungs or causes other complications.

Doctors may use CRP to:

• Watch how the illness is progressing
• Decide if more tests or care are needed
• Track how well your body is fighting the virus

By the way, if you are unsure about your symptoms, try using the Covid Symptom Checker to better understand your condition.

The flu (influenza) can also lead to high CRP levels, though they’re usually not as high as in bacterial infections.
Still, when the flu causes severe symptoms or leads to pneumonia, CRP can rise sharply.

You might notice:

• Sudden fever and chills
• Body aches
• Fatigue that lasts for days

CRP helps show if it's more than just a mild viral illness.

EBV virus causes mononucleosis or “mono,” known for extreme tiredness and swollen glands. CRP levels can go up, especially early on, when the body’s immune system is reacting strongly.

While it’s a virus, the symptoms can last weeks, and CRP may stay elevated during that time.

Some forms of hepatitis, especially acute viral hepatitis, can lead to inflammation in the liver and a rise in CRP levels.

If your CRP is elevated and you also have symptoms like nausea, yellowing of the skin (jaundice), or belly discomfort, doctors may test for liver infections.

Viral infections usually cause mild to moderate increases in CRP, but levels can still be helpful in checking how your body is responding.

Fungal and Parasitic Infections

Candidiasis is a fungal infection caused by yeast, often affecting the mouth, skin, or genitals. In healthy people, it's usually mild. But in people with weakened immune systems, it can become serious and spread to the blood.
When that happens, CRP levels can rise significantly, sometimes similar to bacterial infections.

Doctors may use CRP tests to:

• Spot signs of a deeper or spreading infection
• Monitor how the body is responding to treatment

Aspergillosis mostly affects the lungs and is more common in people with chronic lung problems or weak immune systems.

It may start slowly but can cause inflammation deep inside the lungs. CRP levels tend to increase as the infection grows.

Common signs include:

• Coughing, sometimes with blood
• Chest pain
• Feeling short of breath

A rising CRP may be one of the first signs something more serious is happening.

Malaria is a parasitic infection spread by mosquitoes. It causes cycles of fever, chills, and body aches.

During active infection, CRP levels can go very high, especially if the illness becomes severe or affects multiple organs.

CRP helps indicate how active the inflammation is and whether the body is still under attack.

Toxoplasmosis is another parasitic infection that can raise CRP levels, especially in people with weak immune defenses.

Most people don’t feel symptoms, but when the infection becomes active, it can affect the eyes, brain, or muscles.

If CRP is elevated and the person feels generally unwell, doctors may include toxoplasmosis in their list of possible causes.

When High CRP Isn’t Caused by Infection

CRP levels can be high even when there’s no infection in the body. This is because CRP responds to any kind of inflammation, not just those caused by bacteria or viruses.

Autoimmune Diseases

Conditions like rheumatoid arthritis (RA) or lupus can make the immune system attack healthy tissues. This causes long-term inflammation, and CRP levels can stay elevated for weeks or months. These conditions often cause joint pain, rashes, and fatigue.

Chronic Inflammatory Conditions

Inflammation also plays a role in long-term health problems like:

• Inflammatory bowel disease (IBD): causes belly pain and digestive symptoms
• Obesity: fat tissue produces chemicals that lead to low-grade inflammation

These raise CRP slowly over time, even if you don’t feel sick.

Cancer, Trauma, or Surgery

CRP can rise:

• After major injuries
• Following surgery
• In some types of cancer, especially if they trigger inflammation or tissue damage

Doctors often use CRP levels along with other tests to figure out whether inflammation is caused by infection or something else. That’s why CRP alone doesn’t give a full answer, it’s a clue, not a diagnosis.

Common Symptoms of Infection with High CRP

If your CRP is high because of an infection, your body will usually show other signs too. These symptoms often come on quickly and may include:

• Fever
• Chills or shivering
• Body aches or pain
• Swelling or redness in one area
• Fatigue or low energy
• Cough, sore throat, or pain when peeing (depending on the infection)

You should see a doctor if:

• These symptoms come on suddenly and feel strong
• They last more than a few days
• You feel worse even after resting

CRP levels give doctors extra information to understand what’s going on, but your symptoms still tell the bigger story.

How Doctors Diagnose the Cause of High CRP

Since many things can raise CRP, doctors usually run other tests alongside the CRP test to figure out the exact cause.

Here’s what they might use:

• CBC (Complete Blood Count): Checks if your white blood cells are high, which often points to infection.
• Procalcitonin: Helps tell if the problem is a bacterial infection or something else.
• Blood, urine, or throat cultures: These can find the exact germ causing the infection.
• Imaging tests: Like chest X-rays or ultrasounds if a hidden infection is suspected.

You can upload your blood test results to get a simple, easy-to-understand interpretation.

Doctors may also repeat your CRP test after a few days to:

• See if it’s going up or down
• Check if your body is responding to treatment
• Decide if more tests are needed

A high CRP isn’t dangerous by itself, but it does signal that your body needs attention.

How to Lower High CRP from Infections

Things That Can Help:

• Get plenty of rest: Your body heals faster when you’re well rested.
• Drink enough fluids: Staying hydrated supports your immune system.
• Eat anti-inflammatory foods: These include fruits, vegetables, and foods rich in omega-3 fats like flax seeds and walnuts.
• Avoid smoking and processed foods: These can make inflammation worse.

Small lifestyle changes can help your body recover faster and lower your CRP naturally.