Differential diagnosis of bacterial infection and inflammatory response in kidney diseases using procalcitonin

Early diagnosis of bacterial infection in renal patients remains difficult. Common laboratory parameters, such as white blood cell (WBC) count, erythrocyte sedimentation rate, and C-reactive protein (CRP) may be affected by the underlying disease, uremia or its extracorporeal treatment, or by immunosuppressive drugs. Procalcitonin (PCT) may be useful for the detection of systemic bacterial infections in patients with end-stage renal disease (ESRD) undergoing renal replacement therapy, but elevated PCT concentrations have also been found in a significant number of uremic patients without signs of infection.

We tested whether measurements of PCT levels help distinguish the chronic inflammation in renal diseases from invasive bacterial infections. Serum levels of PCT were compared with the corresponding serum C-reactive protein (CRP) concentrations and WBC counts in 197 patients with different stages of renal disease: Group I) 32 patients with chronic renal failure (serum creatinine 2-6 mg/dL); group II) 31 patients with a functioning renal transplant receiving standard immunosuppressive regimens; group III) 76 clinically stable patients with ESRD undergoing hemodialysis (HD); group IV) 23 patients with chronic renal failure (CRF) due to systemic autoimmune disease; group V) 35 patients with proven systemic bacterial infection and CRF.

PCT levels were within the normal range (< 0.5 ng/mL) in patients with CRF and renal transplant patients without any clinical evidence of bacterial infection, regardless of the degree of renal failure and the underlying disorders. In 22 out of 76 stable HD patients, PCT levels were above the upper limit of normal, but 97% of these values were below the proposed cut-off for chronic HD patients of < 1.5 ng/mL. CRP levels were elevated in 17 of 32 patients with CRF (mean +/- SD: 0.57 +/- 0.49 mg/dL), in 10 of 31 renal transplant patients (0.41 +/- 0.55 mg/dL), in 16 of 23 patients with autoimmune disorders (2.78 +/- 3.21 mg/dL) and in 42 of 76 patients treated by HD (0.64 +/- 0.58 mg/dL). In patients with CRF and systemic bacterial infections, both PCT and CRP were markedly elevated (PCT 61.50 +/- 115.4 ng/mL, CRP 14.50 +/- 10.36 mg/dL), but in contrast to PCT, CRP values overlapped in infected and non-infected patients.

Our data indicate that PCT levels are not significantly affected by loss of renal function, immunosuppressive agents or autoimmune disorders. Thus, significantly elevated PCT concentrations offer good sensitivity and specificity for the early diagnosis of systemic bacterial infection in patients with CRF or patients with ESRD treated by HD. CRP concentrations may be useful indicators for inflammation in patients with renal diseases, but have low specificity for the diagnosis of bacterial infection.