BLOOD CULTURES IN RELATION TO THE CULTURE D BLOOD-VOLUME IN BACTEC 6ABOTTLES

BACKGROUND: Concentration of microorganisms in blood is low in bactere mia from extravascular sources. The best yield from blood cultures is achieved by culturing a minimum of 10-20 ml, although in some processi ng blood culture systems such as Bactec NR-860, smaller volume is used . The objectives of the present study were to establish the frequency in which inadequate small blood volumes are employed for culturing and to analyze the relation between the cultured blood volume in Bactec 6 A bottles and the yield achieved. MATERIAL AND METHODS: We weighed 200 0 Bactec 6A bottles pertaining to consecutive blood cultures obtained from untreated patients with clinical suspicion of infection. The cult ured blood volume was estimated subtracting the mean empty bottle weig ht. RESULTS: Microorganisms were recovered from 251 bottles (12.5%). O ne hundred and thirty one (6.8%) isolates were considered as clinicall y significant and 115 (5.7%) as contaminant. The inoculated blood volu me in both significant (5.532 +/- 1.587 ml) and non-significant (5.471 +/- 1.563 ml) recoveries was superior than that of bottles without mi crobiologic growth (5.209 +/- 1.575 ml, p = 0.016 and p = 0.06, respec tively). A linear positive trend was found between the cultivated bloo d volume and the rate of recoveries (p = 0.008). Within the range of 1 up to 10 ml, the rate of recoveries increased 2.28% for each addition al ml of cultivated blood (r = 0.953, p < 0.0001). Out of the 2,000 we ighed bottles 127 (6.3%) contained less than 3 ml of blood and 576 (29 %) between 3 and 5 ml. CONCLUSIONS: We have proved that the rate of re coveries from Bactec 6A bottles increased with the volume of cultured blood. In untreated patients, this increase is mantained up to volumes of 7 to 10 ml.