Background: Procalcitonin (PCT), the precursor of the calcitonin, is synthesized in the parafollicular C-cells of the thyroid. It has been used to detect and to differentiate systemic bacterial infections from flares of systemic lupus erythematosus (SLE). PCT in serum increases in severe bacterial and fungal infections, but not, or only slightly in viral infections.
Objective: To measure PCT levels in patients with active SLE and to compare them with patients without lupus activity and to determine the possible association between activity and elevation of the PCT.
Design: Prospective case control study.
Patient and methods: Measurements were made of PCT (METHOD: Essay immunoluminometric--and ultrasensitive--BRAHMS Diagnostika, Berlin, Germany), C-reactive protein, erythrocyte sedimentation rate, and blood and urine cultures. The index of activity of SLE was determined by Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) score of a serial group of patients seen by our rheumatology service. Samples from 53 patients were analyzed. The patients were divided in 2 groups: group I (n = 21) with little or no activity for SLE; group II (n = 32) with activity for SLE (SLEDAI >5). None of the patients had severe bacterial infection, sepsis, or systemic multiorgan failure.
Results: Group I had a SLEDAI score of 1.8 [95% confidence interval (CI) 1.09-2.51] with mean levels of PCT 0. 08 ng/mL (Negative smaller than 0. 5 ng/mL). Group II SLEDAI score was 14.6 (95% CI 11.95-17.23) with mean levels of PCT 0.418 ng/mL with standard deviation 1.0021 (95% CI 0.0628-0.773). The measure of association calculated by Fisher method was not significant (1.927) (P = 0. 282). In the group II, 3 patients had frankly positive PCT (3.18, 3.42, and 3.95 ng/mL) and high activity indices (14, 13, and 24). None presented with severe infection, sepsis, or systemic multiorgan failure. They had pneumonia, renal failure (PCT 3.42 ng/mL) and urinary tract infection without systemic symptoms (3.95 ng/mL). Infection was not detected in the other patient (3.18 ng/mL) that was interpreted as a false positive.
Conclusions: This study demonstrates that there is no association between the activity of SLE and PCT levels. The utility of the PCT resides is in raising suspicion of a concurrent bacterial or mycotic infection in the evaluation of patients with active autoimmune diseases.