Volume of blood required to obtain central venous catheter blood cultures in infants and children.

To determine how much blood must be discarded before one can obtain a reliable central venous catheter blood culture, we prospectively cultured the blood (from 96 patients) that is ordinarily discarded before obtaining blood for such a culture. We then compared the prospective culture results with those of the actual blood culture. Three sequentially drawn aliquots of blood were aspirated from the central venous catheter and cultured. The culture results of the second aliquot were comparable to those of the third (the portion usually cultured) in overall sensitivity (94.4%), specificity (94.9%), and positive predictive value (80.9%). Thus, the amount of blood that must be discarded (infants: 0.3 mL; children: 1.0 mL) before one can obtain an accurate central venous catheter culture is less than was previously thought.