Arterial blood sampling changes the steady state of glucose in rats during FDG-PET

Objectives Metabolic rate of glucose (MR) can be measured using quantitative FDG-PET. The method assumes that plasma glucose is at steady state throughout the scan and a constant plasma glucose concentration is used. In this study, we investigated the glucose levels in rats with/without catheter implementation and multiple blood sampling. We also examined whether blood glucose can be measured accurately using a glucose meter.

Methods 23 rats were studied: 8 rats (single studies; n=8) with and 15 rats (multiple studies; n=41) without a femoral artery catheter. Immediately after surgery or being anesthetized, the rat (under 2% isoflurane; temperature 35°C) was injected with 37~110 mCi of FDG through a tail vein. 13 serial blood samples (~100 μL each) were taken from the catheters in 45 minutes. For rats without catheters two blood samples, one (~10 μL) before and one (~100 μL) at 45 minutes after FDG injection, were taken from the contralateral vein. The glucose concentrations were first measured on whole blood using a glucose meter (Accu-Chek® Active; Roche Diagnostics). The plasma glucose was measured using an YSI 2700 Select™ Biochemistry Analyzer.

Results Glucose levels measured using the glucose meter (y; y =0.978x) correlated well (Pearson correlation; r =0.95) with plasma glucose levels from the YSI analyzer (x). The plasma glucose concentrations (11.5±1.0 vs. 10.7±1.7 mmol/L; p>0.05) in rats with or without surgery were within physiologic ranges. At 45 minutes, the rats with 13 blood samples taken had a greater percent change in glucose levels than those with two blood samples taken (28.3%±5.9 vs. 9.5%±1.1; p<0.02).

Conclusions Aspects of the surgery and blood sampling affected glucose levels and therefore had a larger effect on MR measurement using FDG-PET. Derivation of input function without surgery/multiple blood sampling is recommended. A glucose meter is accurate and simplifies the procedure for plasma glucose measurement