(99m) Tc-labelled human serum albumin cannot replace (125) I-labelled human serum albumin to determine plasma volume in patients with liver disease.

Background And Aims: Determination of plasma volume (PV) is important in several clinical situations. Thus, patients with liver disease often have augmented PV as part of their sodium-water retention. This study was undertaken to compare PV determination by two indicators: technetium-labelled human serum albumin ((99m) Tc-HSA) and iodine-labelled human serum albumin ((125) I-HSA), as the former may have advantages at repeated measurements and the latter is the classical gold standard.

Study Population And Methods: In 88 patients, (64 with liver disease, mainly cirrhosis, and 24 patients without liver disease), simultaneous measurements of PV were taken with (99m) Tc-HSA and (125) I-HSA after 1 h in the supine position. Blood samples were obtained before and 10 min after quantitative injection of the two indicators. In a subset of patients (n = 32), the measurements were repeated within 1 h.

Results: In all patients, a close correlation was present between PV determined by the two indicators (r = 0·89, P<0·0001). In all, but twelve patients, a higher PV was obtained with (99m) Tc-HSA compared with (125) I-HSA (P<0·0001). PV determined with (99m) Tc-HSA exceeded PV determined with (125) I-HSA by 367 ml (5·2 ml kg(-1) ) in liver patients as compared to 260 ml (3·5 ml kg(-1) ) in patients without liver disease (P<0·05). The precision of repeated PV determination was 1·75% (coefficient of variation) with (99m) Tc-HSA and 1·71% with (125) I-HSA (ns), and similar values were found in patients with and without liver disease.

Conclusion: The study demonstrates that (99m) Tc-HSA has the same precision as that of (125) I-HSA. However, especially in patients with liver disease, (99m) Tc-HSA consistently overestimates the PV, most likely owing to indicator heterogeneity with subsequent fast removal from the circulating medium with a higher volume of distribution as the outcome.