Finding the right tests…
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Finding the right tests…
Hormonal
Procalcitonin is a protein your body makes in tiny amounts all the time, but a serious bacterial infection makes cells across your body release much more of it into your blood. Your doctor orders this test mainly in a hospital setting, when you're seriously unwell and needs to work out whether a bacterial infection is driving your illness or whether a virus is more likely — a distinction that decides whether antibiotics will actually help. It's also used to judge how severe a bacterial infection or sepsis is, and to track whether treatment is working as the level falls over following days. This is not a general infection screen; it's aimed specifically at telling bacterial and non-bacterial causes apart.
This test reports the level of procalcitonin in your blood, usually in nanograms per millilitre. In someone with a serious bacterial infection, cells throughout the body release procalcitonin, so the number tends to rise with the severity of the infection and fall as treatment works. It's almost always ordered for someone already seriously unwell, typically in a hospital, rather than as a first check for a mild illness at home. A single sample is drawn from a vein, and no special preparation is needed beforehand.
Procalcitonin sits at very low levels in healthy blood, but a bacterial infection that's spreading through the body — as opposed to one staying local — makes tissues across the body release it in much larger amounts. Viral infections generally don't trigger the same response, which is what makes this test useful for telling the two apart.
The main use is in people who are seriously unwell with a suspected infection, where knowing whether bacteria or a virus is responsible changes the treatment. Antibiotics help bacterial infections but do nothing for viral ones, so this test is often used alongside clinical judgement to decide whether starting or continuing antibiotics makes sense — a role sometimes called antibiotic stewardship. It's also used to gauge how severe a bacterial infection or sepsis is, since higher levels generally track with more serious illness and a greater risk of complications such as septic shock.
A level that's normal or only mildly raised makes a severe bacterial infection less likely and a viral or local infection more likely. A level that keeps climbing over repeat tests points to worsening infection, while a falling level over the following days is often used to show treatment is working and that antibiotics might be safely stopped.
This test doesn't identify which bacteria is responsible — for that, your doctor still needs cultures or other targeted tests.
Procalcitonin rises more specifically with serious bacterial infection than general inflammation markers like CRP, and it tends to fall faster once treatment works, which is why it's often used to guide antibiotic decisions. It isn't meant to replace CRP or a white blood cell count — doctors often use them together.
Viral infections generally cause little or no rise in procalcitonin, which is exactly why the test is useful for separating bacterial from non-bacterial causes of illness. A level that stays low despite obvious illness points away from a serious bacterial infection.
It's mostly used for people who are seriously unwell, which in practice usually means it's ordered in a hospital or emergency setting rather than for routine outpatient illness.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Yes. Recent major surgery, severe burns, and some other non-infectious conditions can raise procalcitonin, so your doctor interprets the result alongside your symptoms and history rather than in isolation.
Yes, a falling procalcitonin level over consecutive tests is commonly used to show that treatment for a bacterial infection is working, and can support a decision to stop antibiotics earlier.
No special preparation, including fasting, is needed before this blood draw.