Alberto Magnasco1, Sandro Alloatti. 1. Renal Unit G. Gaslini Institute, Genoa, Italy. alberto.magnasco@ospedale-gaslini.ge.it
Abstract
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 (5 ml) 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: QB 200 ml/min, C2 16-20 s; QB 300 ml/min, C2 13-17 s; QB 400 ml/min, C2 9-12 s. 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.
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 (5 ml) 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: QB 200 ml/min, C2 16-20 s; QB 300 ml/min, C2 13-17 s; QB 400 ml/min, C2 9-12 s. 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.