Procalcitonin

Order Code

---

4709

Preferred Specimen

---

Collect 2 mL Serum using an SST tube. Allow it to clot in an upright position for at least 30 minutes, then centrifuge within 2 hours of collection. Refrigerate the specimen.

Container Type

---

Serum Separator Tube

Alternate Specimen Requirements

---

Acceptable alternatives include:

Collect 2 mL Serum in a plain red-top tube. Allow it to clot upright for at least 60 minutes, then centrifuge and transfer the serum into a plastic transport tube within 2 hours. Label the tube as Serum from Plain Red-Top Tube and Refrigerate.

Minimum Volume

---

• 0.3 mL Serum

Transport Temperature

---

Refrigerated

Expected Turnaround Time

---

2 Days

Specimen Stability

---

• Room Temperature: 24 hours
• Refrigerated: 6 days
• Frozen: 3 months

Methodology

---

Electrochemiluminescence Immunoassay (ECLIA)

Rejection Criteria

---

No more than one freeze/thaw cycle

Overview

---

Procalcitonin (PCT) is the precursor of the hormone calcitonin, which is normally produced by the thyroid C-cells and neuroendocrine cells of the lungs and intestines.
During systemic inflammation, especially bacterial infections, PCT production increases across various tissues and organs. Measuring these elevated levels helps identify bacterial infections and evaluate their severity.

In bacterial infections, PCT levels rise because bacterial endotoxins and cytokines block the conversion of PCT to calcitonin. In contrast, viral infections typically show low PCT levels, since cytokines like gamma interferon do not inhibit this conversion. Similarly, conditions such as gout, inflammatory bowel disease, arthritis, or the use of steroids and NSAIDs rarely cause a significant PCT increase (Gilbert, 2011).

PCT testing has been studied in two main patient groups — outpatients with respiratory tract infections and critically ill ICU patients (Hayashi, 2011). It also plays a role in reducing unnecessary antibiotic use for nonbacterial conditions and shortening treatment durations for bacterial infections.

Clinical Significance

---

• Helps differentiate bacterial infections (requiring antibiotics) from viral or allergic causes.
• Aids in the diagnosis of sepsis and infection severity assessment.
• Monitors treatment response to antibiotics and guides therapy duration.
• Supports antibiotic stewardship, minimizing overuse without affecting outcomes.
• Assists in diagnosing pediatric pneumonia and renal involvement in pediatric urinary tract infections (UTIs).

Additional Information

---

In pediatric UTIs, PCT demonstrates higher sensitivity (90%) and specificity (88%) than C-reactive protein for identifying kidney involvement (Xu, 2014).
While calcitonin (CT) remains the main marker for medullary thyroid cancer (MTC), PCT testing offers advantages — studies show strong correlations between CT and PCT in MTC patients, suggesting PCT can serve as a complementary or alternative marker (Machens, 2014).

Interpretative Information

---

In healthy individuals, PCT ≤0.1 ng/mL is normal. Levels may become detectable within 2–4 hours of systemic inflammation, peaking within 24 hours.
PCT remains elevated during ongoing infection and drops by about 50% daily once effective treatment begins (Schuetz, 2011).

Newborns may show naturally high PCT levels during the first 24–72 hours after birth. However, those with early sepsis have significantly higher PCT values compared to uninfected newborns (Chiesa, 1998).

Cutoff Points for Interpretation

---

Lower Respiratory Tract Infections (Adults) (Clayton, 2013):

• < 0.10 ng/mL – Bacterial infection very unlikely
• 0.10 – < 0.25 ng/mL – Bacterial infection unlikely
• 0.25 – < 0.50 ng/mL – Bacterial infection possible
• ≥ 0.50 ng/mL – Suggestive of bacterial infection

Systemic Bacterial Infection / Sepsis (Adults) (Clayton, 2013):

• < 0.50 ng/mL – Systemic infection unlikely
• 0.50 – < 2.0 ng/mL – Possible systemic infection
• 2.0 – < 10.0 ng/mL – Likely systemic infection; high risk for progression
• ≥ 10.0 ng/mL – Severe sepsis or septic shock likely

Noninfectious Causes of Elevated PCT

---

• Major trauma, surgery, burns, multiorgan failure
• Addisonian crisis, pancreatitis, cirrhosis (Child-Pugh C)
• Myocardial infarction, cardiogenic or hemorrhagic shock
• Heat stroke, peritoneal dialysis
• Certain cancers: medullary thyroid carcinoma, small-cell lung carcinoma, bronchial carcinoid
• Treatment with interleukins or TNF-α
• Parasitic (Plasmodium falciparum) and fungal infections
• Newborns during the first two days of life

Limitations

---

• Should not replace clinical judgment or microbiologic studies.
• Early infections (<6 hours) may show false-negative results; repeat testing in 6 hours is advised.
• Fibrin or particulate matter may lead to false-low readings.
• Localized or subacute infections (e.g., endocarditis) may yield low PCT.
• Antibiotic pretreatment can reduce PCT levels.
• Rare high-dose hook effect may cause false-low results.

References

---

Diagnostic Role

---

PCT is among the earliest and most specific markers for bacterial infections, valuable for monitoring disease progression and treatment response.
While cultures remain the gold standard, results take 24–48 hours. PCT can yield results within hours, making it useful in emergency and ICU settings.

• < 0.1 ng/mL strongly supports a nonbacterial cause.
• > 2.0 ng/mL on ICU admission suggests high risk for severe sepsis.
• A > 30% drop after 24 hours of antibiotics indicates treatment success.

PCT testing (e.g., Vidas Brahms PCT assay) has FDA approval for guiding antibiotic initiation or discontinuation in lower respiratory infections and sepsis (Brooks, 2017).
It should always be interpreted alongside clinical findings, as empiric antibiotics may still be necessary even with normal PCT levels in high-risk cases.

Test Setup Days

---

Monday through Friday AM shift

CPT

---

84145 LOINC:75241-0

Reference Range

<0.10 NG/ML

UNIT CODE	UNIT CODE NAME	ANALYTE	GENDER	AGE	REFERENCE RANGE	UNITS OF MEASURE
4709	PROCALCITONIN	PROCAL	NOT SPECIFIED	ALL	<0.10	NG/ML
4709	PROCALCITONIN	PROCAL	MALE	ALL	<0.10	NG/ML
4709	PROCALCITONIN	PROCAL	FEMALE	ALL	<0.10	NG/ML