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Procalcitonin (PCT) in Serum/Plasma

Published: August 9, 2026Updated: August 16, 2026

This test measures procalcitonin, a precursor protein made by cells in response to bacterial infections. It helps distinguish between bacterial and viral infections.

Quick summary

["Procalcitonin is often checked to guide antibiotic use and monitor serious infections."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
85742-5
Short code
S pneum Da 3 DNA Ct Spec Qn NAA+probe
Synonyms
S pneum Da 3 DNA Ct Spec Qn NAA+probe
Category
coagulation
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
probe-amp-tar
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What Is Procalcitonin Used For?

Procalcitonin is primarily used to identify bacterial infections, especially in cases where other tests or symptoms are unclear. It can help doctors decide whether to start antibiotics or adjust treatment plans, particularly in patients with fever or suspected sepsis.

How Is It Different from Other Infection Tests?

Unlike C-reactive protein (CRP), which rises in both bacterial and viral infections, procalcitonin is more specific for bacterial infections. It’s also less affected by stress or inflammation from non-infectious causes.

When Might You Need This Test?

Your doctor may order a procalcitonin test if you have symptoms like fever, chills, or signs of infection (e.g., pneumonia, sepsis, or severe flu). It’s also used in monitoring patients with chronic illnesses (like COPD or heart failure) who may develop infections more easily.

What to Expect Before the Test

No special preparation is needed. A blood sample will be drawn from a vein, usually in your arm. You may feel a slight pinch, but it’s quick and temporary. If you’re on blood thinners, let your doctor know before the test.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Why It Matters in Diagnosis and Treatment

Short name

PCT

Frequently asked questions

Why is procalcitonin important in diagnosing infections?
Procalcitonin is a key marker because it’s produced almost exclusively by cells responding to bacterial infections. Levels rise early in bacterial infections (like pneumonia or sepsis) and fall when the infection is treated. It’s especially useful in settings where other tests (like blood cultures) take time or are inconclusive.
How does procalcitonin help guide treatment decisions?
High procalcitonin levels may prompt doctors to start antibiotics sooner, especially in severe cases. It can also help determine if a patient’s symptoms are worsening due to infection, allowing for adjustments to care (e.g., hospitalization, IV antibiotics). In some cases, it may help avoid unnecessary antibiotics if the cause is viral.
Can procalcitonin levels change over time?
Yes, procalcitonin levels typically drop within days to weeks after successful treatment of a bacterial infection. This can help doctors track progress and decide when it’s safe to stop antibiotics or switch to oral medication.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy