Blood test
Procalcitonin Test
A procalcitonin test measures a marker that rises with serious bacterial infection, helping to assess infection and guide antibiotic use.
Quick answer
Procalcitonin Test: what it is and what the results mean
Procalcitonin (PCT) is a protein that rises in the blood particularly with bacterial infections. A blood test measures its level to help judge whether a serious bacterial infection is present.
- Why it is done: It is used to help distinguish bacterial from other causes of illness, to assess the severity of infection such as sepsis, and to help decide when antibiotics can be safely started or stopped.
- Understanding results: A higher procalcitonin makes a significant bacterial infection more likely and can indicate severity, while a low and falling level supports stopping antibiotics.
What it is
Procalcitonin (PCT) is a protein that rises in the blood particularly with bacterial infections. A blood test measures its level to help judge whether a serious bacterial infection is present.
Why it is done
It is used to help distinguish bacterial from other causes of illness, to assess the severity of infection such as sepsis, and to help decide when antibiotics can be safely started or stopped.
What to expect
It is a standard blood test from a vein in the arm. In hospital it is often repeated over time to track the course of an infection and response to treatment.
Understanding the results
A higher procalcitonin makes a significant bacterial infection more likely and can indicate severity, while a low and falling level supports stopping antibiotics. Results are always interpreted alongside the clinical picture.
Good to know
Risks and limitations
It is a safe blood test but not perfect: some bacterial infections give low levels and some non-bacterial situations raise it, so it supports rather than replaces clinical judgement.
Education and reference only. This explains the test in general terms and is not medical advice. Always follow the specific instructions from the team arranging your test, and discuss your results with your clinician.
Answers
Procalcitonin Test: frequently asked questions
Can procalcitonin tell if I need antibiotics?
It helps guide the decision. A low level makes serious bacterial infection less likely and can support avoiding or stopping antibiotics, but the decision always considers your symptoms and other tests too.
How is procalcitonin different from CRP?
Both are infection and inflammation markers, but procalcitonin tends to rise more specifically with bacterial infection, whereas CRP rises with many types of inflammation. They can be used together.
Related tests
Other blood test investigations
Sources
Where this is drawn from
- NHS — Tests and treatments
- NICE — diagnostic guidance
- Association for Laboratory Medicine / relevant professional body
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