Glucose infusion test (GIT) compared with the saline dilution technology in recirculation measurements

Background. Glucose infusion test (GIT) is a new method to measure vascular access recirculation (R) based on basal glucose increase in the arterial blood line after a 20% glucose bolus (5ml) into the venous chamber. Methods. We compared GIT with the ultrasound dilution method (HD01, Transonic Systems Inc., USA) in a circuit reproducing in vitro the phenomenon of R. We repeated the comparison in 162 chronic haemodialysis patients (133 fistulae, 17 central venous catheters, 12 prosthetic grafts). Results. In vitro, we determined the timing for C2 sampling: Q _B 200ml/min, C2 16-20s; Q _B 300ml/min, C2 13-17s; Q B 400ml/min, C2 9-12s. GIT showed no false positives nor false negatives (100% specificity and sensitivity) while HD01 did not recognize three cases with R = 5% (91% sensitivity) and it yielded no false positive (100% specificity). The Bland-Altman analysis showed a bias of 0.2 ± 1.3% and 1.3 ± 2.9% for GIT and HD01, respectively. In vivo, only 16 out of 162 patients were found positive with both methods (GIT 13.5 ± 13%; HD01 16.3 ± 15%; P = NS) while three patients with minimal R (GIT 3.2%) were not recognized by HD01 although a low R peak was clearly evident and repeatable on the laptop plot. The Bland-Altman analysis showed an overall bias of 0.2 ± 1.7% to the limits of agreement = -3.1 and 3.6% (n = 162) and no correlation between the difference and the mean of positive tests. The pooled coefficient of variation of positive cases was 13.3 and 18.1% for GIT and HD01, respectively. Discussion. Our in vitro study showed a good performance of GIT and its better sensitivity compared to HD01. These results were confirmed in vivo with only 3/162 discordant results due to a low R under the HD01 limit of detection (R = 5%). In conclusion, the GIT proved to be a very accurate screening test for R, with a very low threshold of detection. In addition, it is simple, user-friendly and inexpensive.