Evaluation of swirling, pH, and glucose tests for the detection of bacterial contamination in platelet concentrates

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Abstract
Although infrequent, episodes of transfusion-associated bacterial sepsis may lead to serious outcomes or death and therefore are of concern. This study evaluates the sensitivity of three surrogate tests for the presence of bacteria in platelet concentrates: cessation of swirling, low extracellular pH, and low plasma glucose levels. Day 0 platelet concentrates were inoculated with low levels of one of seven bacterial strains and stored with agitation at 20 to 24 degrees C for up to 5 days. In the morning and afternoon of each day of storage, bacterial levels were ascertained by quantitative plate culture, and platelet concentrates were tested for platelet pH, plasma glucose, and swirling. Quantitative and semiquantitative dipstick techniques were used to determine pH and glucose levels. Platelet concentrates had attained stationary phase growth of Streptococcus pyogenes, Staphylococcus aureus, Escherichia coli, Bacillus cereus, Enterobacter cloacae, Streptococcus mitis, or Staphylococcus epidermidis (> or = 10(7) -10(8) colony-forming units [CFU]/mL) before either the swirling or dipstick methods suggested the presence of bacteria. The sensitivity of swirling and glucose tests for detecting bacterial contamination in platelet concentrates was generally comparable. Although the sensitivity of the pH test was generally similar to that of swirling and glucose tests for most bacteria, platelet concentrates contaminated with E. cloacae had normal pH despite the presence of high levels of bacteria (> or = 10(7)-10(8) CFU/mL). The sensitivity in detection of bacteria in platelet concentrates by the swirling technique or by measuring extracellular pH or plasma glucose is less than the sensitivity reported for microscopy with Gram stain (10(5)-10(6) CFU/mL), fluorescence microscopy with acridine orange stain (10(4)-10(5) CFU/mL), chemiluminescence detection of ribosomal RNA (10(3)-10(4) CFU/mL), and automated bacterial culture (1 CFU/sample volume).