Utilization of Platelet-Rich Plasma (PRP) in the Performance of Blood Cultures

Abstract

Sepsis is a leading cause of death and morbidity. A precise microbiologic diagnosis in these patients reduces mortality, morbidity, hospital length of stay and costs. Current blood culture technology is woefully inadequate in the detection of circulating bacteria, with detection rates in the range of only 32 to 71%. Platelets play a key role in innate immunity. Platelets interact directly with innate immune cells, exert important immunomodulatory effects, and promote leucocyte migration to sites of infection. During active bacterial infection, platelets release platelet factor -4 which binds onto a variety of bacterial surfaces, thus rendering bacteria more susceptible to opsonization by leucocytes. Platelet surface Toll-like receptors play a key role in regulating bacterial phagocytosis by leucocytes. FcgammaRllA mediates immune complex mediated platelet activation for killing of opsonized bacteria. Platelets also have been observed to “corral” circulating bacteria by forming hollow spheres around them. For these reasons, we performed a prospective pilot study involving 100 patients with suspected sepsis testing the hypothesis that BC performed with PRP is superior to traditional BC performed with whole blood in detecting circulating bacteria. PRP was prepared via centrifugation of blood contained in 3 cc CBC tubes containing EDTA obtained upon admission. PRP and whole blood were injected into separate and identical culture media bottles and cultures were incubated identically in our state-of-the art microbiology laboratory. PRP culture technique detected two patients with circulating bacteria in whom traditional blood cultures were negative: Enterobacter faecalis in an elderly woman with bilateral pneumonia and Burkolderia capecia in an immunocompromised elderly man with pneumonia. In two patients with urosepsis culture results were concordant with identification of E. coli in both techniques. In eight patients, traditional BC technique detected circulating bacteria, wherein PRP-generated cultures were negative: three with Klebsiella pneumoniae, two with Enterococcus faecalis, two with E. Coli, and one with anaerobic Bacteroides Theta-iota group. Three positive cultures generated by traditional methodology were deemed contaminants by I.D. consultation. No contaminants or false positives were detected by the PRP-generated technique. Thus, in this pilot study, evaluating the utility of blood cultures prepared from platelet-rich-plasma, two patients were detected to harbor pathogenic circulating bacteria which was undetected by standard state-of-the-art blood culture techniques. Two distinct disadvantages of BC prepared from PRP relative to traditional BC technique in this study were the time delay in preparing PRP from the patient's CBC tube: these had been stored in the lab for typically 4 to 48 hours before centrifugation and subsequent inoculation, and the dramatic difference in volume represented by PRP vs. traditional BC: typically .5 to 1.1 cc vs. 32 to 40 cc, respectively. An additional disadvantage was the presence of EDTA in CBC tubes, which is confirmed to exert antibacterial properties. The results of this pilot study are intriguing. Further studies comparing PRP-generated BC and traditional BC in the detection of circulating bacteria with emerging identification techniques such as metrogenomic analysis in detecting bacterial DNA, RNA or peptide signatures would be interesting.