Rapid identification of bacterially contaminated platelets using reagent strips: Glucose and pH analysis as markers of bacterial metabolism

BACKGROUND: One in every 1000 units of platelets is bacterially contaminated, which puts patients at risk for transfusion-associated sepsis and death. However, there is currently no screening test in place to detect contaminated units. The use of commercially available multiple-reagent urine dipsticks for this purpose was evaluated. STUDY DESIGN AND METHODS: Platelet concentrates were inoculated with either sterile saline or suspensions of Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Klebsiella pneumoniae, or Serratia marcescens to a final concentration of 50 colony-forming units (CFU) per mt. The platelets were analyzed daily by the use of multiple-reagent strips, quantitative culture, and glucometry. RESULTS: B. cereus grew rapidly, reaching 10(7) CFU per mt I day after inoculation, while S. epidermidis grew slowly, achieving similar concentrations 4 to 6 days after inoculation. Two of 10 dipstick reagents, glucose and pH, proved useful in detecting bacteria. Both were lower in bacterially contaminated units than in controls. Glucose data obtained from automated analyzers validated the dipstick data. All organisms were detected at concentrations greater than or equal to 10(7) CFU per mt, and S. aureus and K. pneumoniae were detected in the range of 10(3) to 10(5) CFU per mt. CONCLUSION: The multiple-reagent test used had a sensitivity and specificity of 95 percent (greater than or equal to 10(7) CFU/mL) and 98 to 100 percent, respectively. These data indicate that urine dipsticks can be used to rapidly and inexpensively detect bacterial contamination in platelet concentrates, which potentially will reduce morbidity and mortality at minimal cost.