Autor(s): M. Schinella, G. Lippi, V. Curci, P. Gualdi, L. Collini, M. Mattarei
Background. Distinguishing sepsis from other non-infectious conditions in critical patients with clinical signs of acute inflammation is challenging. Procalcitonin (PCT) has recently been now acknowledged as one of the most useful laboratory parameters for increasing the accuracy of diagnosing sepsis, for monitoring patients at high risk, for prognostic assessment and therapeutic control, but little information is available on its relationship with blood culture test and C reactive protein (CRP). Therefore, the aim of this study was to compare PCT with CRP and blood culture from a laboratory standpoint.
Methods. A total of 1358 samples referred for PCT testing were considered. All the samples were from patients hospitalised at the Rovereto Hospital and other facilities pertaining to Trento Provincial Health Service (APSS). PCT was measured using EDTA plasma specimens on the automatic analyser KRYPTOR, whereas CRP was measured by an Olympus latex-amplified immunoturbidimetric assay. Bactec 9240 was used to detect bacterial growth in the blood samples. A total of 798 samples for measurement of CRP were also processed, along with 1529 blood culture specimens.
Results.1343 (88%) out of the 1529 blood culture performed were negative and 186 (12%) were positive. 861 (63%) tests yelded to a PCT level below the detection limit of the assay (0.5 ng/ml). Of these 798 C-reactive protein tests, 728 were significant, above 6 mg/l, and just 70 were not significant.
In our study, the highest value of PCT observed was 352 ng/mL, associated with four positive blood culture vials where Escherichia coli was isolated. The microorganisms most frequently isolated were: Staphylococcus epidermidis 20, Escherichia coli 16, Staphylococcus aureus 8, Staphylococcus hominis 6, Streptococcus pneumoniae 4, Klebsiella pneumoniae 3, Pseudomonas aeruginosa 3.
The following pathogenic microorganisms were isolated in the positive blood culture vials, associated with low PCT values (<2 ng/mL): Staphylococcus epidermidis 16, Staphylococcus hominis 4, Staphylococcus aureus 3, Escherichia coli 3, Corynebacterium spp.. The following pathogenic microorganisms were isolated in the positive blood culture vials, associated with intermediate PCT values (from ≥2 to <10 ng/mL): Escherichia coli 4, Staphylococcus epidermidis 2, Staphylococcus aureus 2, Streptococcus pneumoniae 2, Haemophilus influenzae 2. The following pathogenic microorganisms were isolated in the positive blood culture vials, associated with high PCT values (≥10 ng/mL): Escherichia coli 9, Staphylococcus aureus 3, Staphylococcus epidermidis 2, Staphylococcus hominis 2, Streptococcus pneumoniae 2, Pseudomonas aeruginosa 2.
Conclusions. Although we found a strong correlation between positive blood culture tests and high PCT values, some positive blood cultures have near to normal levels. Overall, gram-positive blood culture tests were clearly associated with the PCT levels moderately higher than the diagnostic threshold, whereas gram-negative blood cultures were associated with considerably higher. We also found a good agreement between negative blood cultures and PCT values, either lower than the diagnostic cutoff or comprised between 2.0 and 10.0 ng/mL, allowing us to conclude that PCT has a high negative predictive value. Procalcitonin is far more specific and reliable than C-reactive protein as regards systemic inflammation. Unlike procalcitonin, PCR increases greatly in localised inflammation, but does not reflect inflammatory condition patterns equally well.
Taken together, our results confirm that measurement of PCT would be suitable to provide important indications for the therapeutic control of infection, contributing to a potential reduction in antibiotic treatment.
Key-words: Sepsis, PCT, CRP, bacteremia.