New techniques for diagnosing catheter-related infection

Catheter-related infections (CRI) are a significant cause of morbidity and mortality. A definite diagnosis of CRI usually requires the removal of the catheter for catheter-tip culture. However, only about 20% of the central venous catheters removed because infection is suspected actually prove infected. Diagnostic techniques have been proposed to establish the diagnosis of CRI and to avoid unjustified removal of the catheter. For this purpose, methods such as skin cultures at the catheter-exit site have a high negative predictive value. When quantitative blood cultures are drawn simultaneously from the catheter and a peripheral vein, a central to peripheral blood culture colony count ratio of 5:1 to 10:1 is highly predictive of CRI. Recently, the measurement of the differential time to positivity between hub- and peripheral blood cultures has been proposed for diagnosis of CRI without catheter removal. Earlier positivity of cultures of blood drawn simultaneously from central versus peripheral veins is highly correlated with CRI. By using a cutoff value of +120 minutes, the differential time to positivity of the paired blood samples had 91% specificity and 94% sensitivity. The method seems to be effective for both long-term and short-term catheters, and can be performed easily in routine clinical practice. Direct examination using acridine-orange leucocyte cytospin test and Gram stain on through-catheter blood sample is proposed for rapid diagnosis of CRI. The technique requires 100 μL of catheter blood and the use of light and ultraviolet microscopy. This method compares favorably with other diagnostic methods, and can permit early targeted antimicrobial therapy.