Transcapillary escape rate of 125I-albumin in relation to timing of blood sampling: the need for standardization

Abstract

AbstractBackgroundIncreased vascular permeability is an early sign of vascular damage and can be measured with the transcapillary escape rate of albumin (TERalb). Although TERalbhas a multi-exponential kinetic model, most published TERalbdata are based on mono-exponential kinetic models with variation in blood sampling schemes. Aim of this posthoc study was to evaluate the influence of variation in blood sampling schemes and the impact of mono- or bi-exponential analyses on the calculation of TERalb. Study participants were part of a cross-over intervention study protocol, investigating effects of sodium loading on blood pressure, endothelial surface layer and microcirculation. Multiple blood samples were drawn between 3 and 60 min after injection of radioactive iodide labeled human serum albumin (rHSA).ResultsIn total 27 male participants with 54 measurements were included. For all participants the maximum serum radioactivity was reached within 20 min, while 85% of the participants had their maximum serum activity within 10 min. The TERalbcalculated with the subsequently chosen T20–60 minreference scheme (6.19 ± 0.49%/h) was significantly lower compared to the TERalbof the T3–60 min, T5–60 min, and Tmax – 60 minschemes. There was no significant difference between the T20–60 minreference scheme and the T10–60 minand T15–60 minschemes. Bi-exponential kinetic modeling did not result in significant different observations compared to the mono-exponential kinetic analysis.ConclusionsAs there is variation in the timing of the maximum serum radioactivity of rHSA, blood sampling schemes starting before 10 min after administration of rHSA will result in a significant overestimation of TERalb. In addition, variation in kinetic modeling did not result in significant changes in TERalb. Therefore, we emphasize the need to standardize TERalband for practical and logistical reasons advocate the use of a mono-exponential model with blood sampling starting 20 min after rHSA administration.