The predictive value of procalcitonin serum levels to detect or rule out ba
cteremia was investigated prospectively in a case-control study with 200 ho
spitalized adults from whom blood samples were taken for culture. Fifty bac
teremic patients (cases) had higher procalcitonin serum levels than the 150
controls with sterile blood cultures (11.7 vs. 0.7 ng/ml; P=0.0001), a dif
ference that remained significant after controlling for potential confounde
rs in multivariate analysis. At cut-off values of 0.5 and 0.2 ng/ml, the se
nsitivity of procalcitonin was 56 and 92%, and the specificity was 83 and 4
3%, respectively. These results yielded low positive (22 and 12%) and high
negative predictive values (96 and 99%), reflecting primarily the low preva
lence of bacteremia among patients who undergo blood cultures in hospitals
(low pretest probability). Although caution is mandatory when using such ma
rkers at the individual level, procalcitonin, possibly together with other
parameters, could nonetheless prove useful in future studies to rapidly rul
e out bacteremia.