Does lupus increase procalcitonin levels?

Procalcitonin Levels in Lupus Patients

Lupus does not typically increase procalcitonin (PCT) levels, and normal PCT values can help differentiate lupus flares from bacterial infections in SLE patients. 1, 2

PCT in Lupus vs. Bacterial Infection

• PCT levels generally remain within normal range during lupus disease flares, making it a useful biomarker to distinguish between disease activity and bacterial infection 1
• Studies have consistently shown that PCT levels are not significantly elevated in SLE patients experiencing disease flares without infection 2, 3
• When PCT is elevated in an SLE patient, bacterial infection should be strongly suspected, especially with values >0.38 ng/mL 3

Diagnostic Value of PCT in SLE

• PCT has high negative predictive value (94%) for ruling out bacterial infection in lupus patients when levels are <0.17 ng/mL 4
• PCT is more reliable than CRP for differentiating bacterial infection from disease activity in SLE patients with active disease (SLEDAI >10) 3
• In one study, a PCT cutoff value of 0.38 ng/mL demonstrated 74.5% sensitivity and 95.5% specificity for detecting bacterial infection in SLE patients 3

Clinical Application in SLE Management

• When evaluating febrile SLE patients with SIRS (Systemic Inflammatory Response Syndrome), elevated PCT levels strongly suggest infection rather than disease flare 5
• PCT levels typically decrease following effective antibiotic treatment in infected SLE patients, making it useful for monitoring treatment response 3
• A multi-biomarker approach including neutrophil CD64 expression, presepsin, and PCT provides better diagnostic accuracy for infections in SLE patients 5

Important Caveats and Considerations

• Male SLE patients may have higher baseline PCT levels than females, which should be considered when interpreting results 1
• Some studies have reported conflicting results regarding PCT's utility in SLE, highlighting the need for clinical correlation 2
• C-reactive protein (CRP) may be more useful than PCT for detecting infection in SLE patients who are in disease remission 4
• The European League Against Rheumatism (EULAR) notes that CRP in SLE is controversial, with elevated levels (especially >50 mg/L) suggesting superimposed infection rather than disease activity 6

Clinical Decision Algorithm

1. Measure PCT in febrile SLE patients with suspected infection
2. If PCT <0.17 ng/mL: Likely disease flare rather than infection (94% NPV) 4
3. If PCT >0.38 ng/mL: Strongly suspect bacterial infection (92.1% PPV) 3
4. For values between 0.17-0.38 ng/mL: Consider additional biomarkers (neutrophil CD64, presepsin) and clinical presentation 5
5. Monitor PCT levels during antibiotic treatment to assess response 3