Procalcitonin: what it is, what it tells you and when it’s tested

Procalcitonin is a protein that rises sharply when your body is fighting a bacterial infection. It is a hospital and emergency department test: your doctor reads it together with an examination and other tests. If you feel very unwell, with a high fever and confusion, breathlessness or cold, blotchy skin, call 112 or go to the emergency department.

When it’s tested

Doctors order it when they suspect a serious bacterial infection: pneumonia, a blood infection, sepsis. It also helps them decide, day by day, when an antibiotic can be stopped.

There is no point measuring it when you feel well. In a healthy person it is almost zero, and it says nothing about your health or prevention.

That is why it is not in the Rosa panel. For a check-up, Rosa measures high-sensitivity CRP and white blood cells, which pick up mild inflammation. They do not replace seeing a doctor if you feel unwell.

What it tells you, and what it does not

If it is high, a bacterial infection is more likely. The higher it is, the more serious the infection may be.

If it is low, a serious bacterial infection is less likely. With viruses, such as flu and COVID, it usually stays low.

It is not enough on its own, though. It can be low early in an infection and high without one, for example after surgery. That is why your doctor always reads it with your symptoms and an examination.

That is why it is read together with other tests:

Normal procalcitonin levels

In a healthy person it is very low: many labs give a value below 0.05 ng/mL.

There is no single cut-off for infection, though. Many lab reports flag values above 0.5 ng/mL. On hospital wards two cut-offs are often used: 0.25 for someone with a mild or moderate infection, 0.5 for someone who is seriously ill.

What a number means depends on the picture: the type of infection, whether you are in intensive care, whether you have had surgery. That is why the doctor who examined you reads it.

If your procalcitonin is high or low

Why procalcitonin rises

Usually because of a bacterial infection. Sometimes for other reasons:

Procalcitonin and CRP: what is the difference

CRP rises with almost any inflammation: a bacterial or viral infection, an autoimmune disease, an injury.

Procalcitonin is more closely tied to bacteria. It rises within hours and falls quickly as the infection heals. That is why it helps decide when to start or stop an antibiotic.

In studies, using procalcitonin to guide antibiotics in chest infections cut the number of antibiotic days without making recovery worse.

When to worry

This test is not one to read on your own. How you feel is what counts:

Frequently asked questions

What are normal procalcitonin levels? In a healthy person it is below 0.05 ng/mL for many labs. Many lab reports flag values above 0.5. What it means depends on the picture, though: your doctor reads it.

High procalcitonin: what does it mean? Usually that there is a bacterial infection, sometimes a serious one. It can also rise after surgery, an injury or a burn. Your doctor reads it together with an examination and other tests.

What is the difference between procalcitonin and CRP? CRP rises with any inflammation. Procalcitonin rises mainly with bacterial infections, and falls quickly as they heal. That is why it helps with decisions about antibiotics.

Does procalcitonin rise with COVID? Usually not: with viruses it stays low. If it rises, the doctor thinks of an added bacterial infection or a severe illness.

Can I measure it to know whether I need antibiotics? No, it is not enough on its own. If you have a fever or an infection, talk to your doctor: they decide whether tests are needed and which ones. Do not take antibiotics on your own.

Does Rosa test procalcitonin? No. It is a hospital test, for people who are unwell. Rosa measures high-sensitivity CRP and white blood cells, which are useful for a check-up when you feel well.

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