The purpose of the present study is to compare plasma volume determination by 99mTc-labeled albumin with 125I-labeled albumin. Fifteen subjects will be enrolled. The hypothesis is that plasma volume determined by the different methods are the same.

For many years, radioiodinated albumin has been "the golden standard" for measurement of plasma volume. There are a number of clinical situations in which a nuclide with a shorter half-life would be preferred. Furthermore, due to periodic lapses in the availability in the delivery of 125I-labeled albumin, there is a need to evaluate another nuclide as a tracer for plasma volume determination.

99mTc-labeled albumin is easily prepared by a simple and reproducible method with a high labeling efficiency and short half-life.

In this study, we want to compare plasma volume determined by 99mTc-labeled albumin with plasma volume determined by 125I-albumin (golden standard). In both procedures, plasma volume is estimated from multiple postinjection samples for accurate zero-time extrapolation in order to correct for leakage of labeled albumin from the vascular compartment.

Inclusion Criteria:

• BMI < 27 kg/m2
• Written informed consent

Exclusion Criteria:

• Hypertension (140/90 mmHg)
• Diabetes mellitus
• Any use of medication
• Pregnancy