^99mTc-albumin can replace ¹²⁵I-albumin to determine plasma volume repeatedly

Abstract

Objective. Plasma volume assessment may be of importance in several disorders. The purpose of the present study was to compare the reliability of plasma volume measurements by technetium-labeled human serum albumin (^99mTc-HSA) with a simultaneously performed plasma volume determination with iodine-labeled human serum albumin (¹²⁵I-HSA). Materials and methods. In 15 healthy volunteers, simultaneous plasma volume measurements with ^99mTc-HSA and ¹²⁵I-HSA were performed after ½ hour in the supine position. Blood samples were obtained 10, 15, 20, and 30 minutes after the injection for accurate retropolation from the plasma counts to time zero to correct for leakage of the isotopes from the circulation. Results. The mean difference (bias) between plasma volume measured with ¹²⁵I-albumin and ^99mTc-albumin was 8 ml (0.1 ml/kg) with limits of agreement (bias ±1.96 SD) ranging from –181–196 ml (−2.3–2.5 ml/kg). The tracer disappearance rate was significantly higher with ^99mTc-albumin (−23.1±7.1%/h) than with ¹²⁵I-albumin (−6.7±3.6%/h) (p <0.001). Conclusion. This study demonstrates that ^99mTc-HSA can replace ¹²⁵I-HSA for single measurements of plasma volume in healthy volunteers. It needs to be emphasized however, that repeated blood sampling for 1/2 hour after injection of the tracer is required to correct for the disappearance of ^99mTc and ^99mTc-HSA from the circulation.

Key Words::

• Plasma volume
• blood volume
• 99mTc-human serum albumin; 125I-human serum albumin
• indicator dilution method

Acknowledgements

We would like to thank Maibritt Arnesen for excellent technical assistance and for her contribution to the design of the study.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.