Objective Thrombocytopenia is frequently observed during bloodstream infection (BSI); however, little is known about the trends in platelet size during BSI. The aim of this study was to investigate trends in platelet indices during BSI and to determine the relationship between the mean platelet volume (MPV) levels and the prognosis of BSI patients.
Methods We conducted a four-year retrospective study to assess the trends in the platelet indices and the clinical features of BSI. We enrolled 350 patients with positive blood cultures and measured the platelet indices during five periods: 30 to seven days before onset (1st period); within one day of onset (2nd period); three to five days after onset (3rd period); seven to 10 days after onset (4th period); and 14 to 19 days after onset (5th period). The end point was defined as 30-day mortality.
Results Among the BSI patients, the average platelet count decreased during BSI (29.4 ^*10⁹/L to 24.0 ^*10⁹/L, p<0.001), while the average MPV level increased (7.33 fL to 7.89 fL, p<0.001). The degree of MPV elevation in the nonsurvivors (n=25) was lower than that observed in the survivors (n=325) between the 1st and 2nd periods (0.00 fL vs. 0.35 fL, p=0.006), whereas between the 2nd and 3rd periods, the degree of MPV elevation in the nonsurvivors was higher than that observed in the survivors (0.74 fL vs. 0.19 fL, p=0.03). MPV elevation after BSI was identified to be a negative prognostic factor for BSI (odds ratio: 1.82; 95% confidence interval: 1.00-3.32; p=0.027).
Conclusion Changes in the MPV levels after BSI may therefore be a useful prognostic marker for BSI.