Denatured radioiodinated human serum albumin (DHA) clearance studies at a dose of 1 mg/kg body wt., were carried out in 16 thalassemic children, prior to and 7-10 days following blood transfusion, to investigate changes of the effective RES blood flow which might accompany the posttransfusion spleen size diminution. A statistically significant increase (P less than 0.001) of the DHA plasma clearance rate was observed 7-10 days following blood transfusion denoting an increase of the blood flow to the effective RES while at the same time the spleen diminished in size. It is suggested that changes in the effective RES blood flow in these patients are directly related to changes in the intrasplenic circulatory capacity.

The plasma clearance rate of heat denatured human serum albumin (DHAI-125, 5 mg/kg body weight) was studied in 20 children with homozygous-beta-thalassemia before and 7--10 days after blood transfusion. A significant increase of the DHAI-125 clearance rate (P less than 0.02) was found 7--10 days after blood transfusion while the spleen presented its minimum size. This finding may be relevant to the improved intrasplenic blood circulation after blood transfusion due to the release of the blood trapped within the spleen.

The kinetics of heat‐damaged homologous red blood cells (HDE) was studied prior to and 7–10 d following blood transfusion in 14 patients with homozygous ß‐thalassemia. On the basis of our results, ß‐thalassemic patients were classified into two distinct groups. In the first group the pretransfusion HDE extraction efficiency of the spleen was significantly lower than that of the second group and it increased dramatically following blood transfusion. On the contrary, the relatively higher pretransfusion HDE extraction efficiency of the patients of the second group showed a significant decrease after blood transfusion. These differences between the two groups of ß‐thalassemics might be attributed to the different qualitative as well as quantitative alterations of the splenic vascular bed occurring in these patients during the course of their disease. Furthermore, there was convincing evidence that part of the HDE mixture was extracted by RES sites outside the spleen, a function which is also affected by blood transfusion.

The parameters of 51Cr labelled red cell survival curves were calculated in 33 patients with homozygous beta-thalassaemia, 8 with sickle-cell anaemia and 3 with s -- beta-thalassaemia, using a non-linear weighted least squares analysis computer program. In thalassaemic children the calculated parameters denote that the shortening of the mean cell life is due to early senescence alone, while there is some evidence that in thalassemic adults additional extracellular destruction mechanisms participate as well. Red cell survival curves from patients with sickle-cell anaemia and s -- beta-thalassaemia resemble each other, while their parameters indicate an initial rapid loss of radioactivity, early senescence and the presence of extracellular red cell destruction factors.

In order to investigate the effect of blood transfusion on the RE cell function in thalassemia major, 14 children with homozygous β thalassemia were studied prior to and 7 to 10 d following blood transfusion, when, according to previous studies, spleen reaches its minimum size. The denatured human albumin (DHA) low and large dose clearance techniques were used in order to estimate the maximum RES phagocytic capacity. It is shown that, despite the confirmed post‐transfusion high hepatosplenic circulation, the RE cell phagocytic capacity is not significantly affected. Furthermore the RES phagocytic capacity of β‐thalassemics is shown to be significantly higher than that of normal controls, and this can probably be attributed to the RES hyperplasia accompanying the disease.