Present methods for measuring red cell volume are based on the dilution of radioactively labelled cells. This precludes the investigation in neonates and pregnant women. We present a simple method for labelling red cells with biotin. These cells may be injected intravenously and subsequently detected using streptavidin-FITC and flow-cytometry. A comparison of the red cell volume estimated using both 51Cr and biotin labelled cells in 19 patients showed no consistent clinically significant difference between the two. This novel label appears to allow red volume to be reliably estimated without using radioactivity.

ABSTRACT. Determination of circulating red cell volume (RCV) in anemic preterm infants is, in theory, a better indicator of transfusion needs than Hb concentration. Our study reports the results of RCV measurement using biotin labeling of red cells on 40 occasions in preterm infants of 25-34 wk gestation. In 20 infants, who had estimations made within 24 h of birth, the RCV varied between 17.7 and 66 mL/kg. Twenty measurements were made at a later age at the time of a blood transfusion. RCV values were between 13.1 and 41.5 mL/kg before transfusion. In 13 infants, RCV was determined simultaneously using two methods, biotin and dilution of autologous HbF with donor HbA at transfusion. There was no significant difference between the results of RCV estimations using these two methods. Our study demonstrates that biotin labeling is an effective method for determining RCV in preterm infants. The RCV represents the total volume of red cells in the circulation. It has been suggested that the RCV is a better guide to red cell transfusion requirements than Hb concentration (l-3), which has been shown to be a poor predictor of benefit from blood transfusion (4-6). After acute blood loss and in anemia of prematurity, the Hb concentration is poorly correlated with RCV; some infants have a very low RCV, yet maintain an adequate Hb concentration (1, 2, 7). RCV may also be a more rational physiologic indicator than Hb concentration of the oxygen carrying capacity of the blood in the whole circulation (3). Low RCV at birth is associated with birth asphyxia (8, 9), increasing severity of hyaline membrane disease (9, lo), and increased mortality (8, 10). RCV estimation has become a vital investigation in adults with polycythemias, some anemias, and the assessment of erythropoiesis (1 1).Previously described methods for determining RCV include both techniques using the dilution principle after labeling of red cells with a tracer and indirect methods, which give a calculated RCV derived from plasma volume and Hct. Radioisotopes as tracers (1 1 iably to overestimate plasma volume. Accurate calculation of RCV from plasma volume requires not only accurate plasma volume estimation but also a knowledge of the total body Hct. Although correction factors allow for the difference between venous and total body Hct (14, 15, 16), they are of quite unknown reliability in sick infants. RCV can be estimated using dilution of autologous HbF at the time of a blood transfusion (2, 17). This is reliable provided that HbF estimation is accurate (e.g. alkali denaturation technique) (2) and at least 20% of the Hb in the circulation before transfusion is fetal. This technique cannot be used without a donor blood transfusion.A new method has recently been described for determination of RCV in adults. Biotin is used to label autologous red cells, and their dilution is quantitated in a fluorescence-activated cell sorter using the fluorescein-streptavidin reaction (17). Biotin is not toxic in infants, even in pharmacologic doses (1 8).We report here results...

SUMMARY In 52 normal subjects there was an inverse relationship between serum ferritin concentration and iron absorption. In 21 measurements in 15 patients with idiopathic haemochromatosis there was a similar inverse relationship but absorption was higher in relation to iron stores at all levels. Haemochromatotic patients with normal serum ferritin levels had abnormally high values for desferrioxamine chelatable iron and there was no correlation between chelatable iron and iron absorption.Iron balance is maintained by the regulation of iron absorption. The precise mechanism is poorly understood (Jacobs, 1973) and one of the outstanding problems is the relationship of iron stores to absorption. Heinrich (1970) (Bentley and Williams, 1974).More recently, the concentration of ferritin in serum has been shown to relate closely to iron stores in normal subjects and in those with iron deficiency or overload (Jacobs, Miller, Worwood, Beamish, and Wardrop, 1972;Walters, Miller, and Worwood, 1973a;Siimes, Addiego, and Dallman, 1974). The assay of ferritin can be carried out in a reproducible manner on a small serum sample, and a preliminary study indicated an inverse relationship between serum ferritin concentration and iron absorption in normal subjects (Walters, Thompson, Jacobs, and Wood, 1973b). This assay has been used in the present study to confirm the relationship between iron stores and iron absorption in normal subjects and to compare it with data from patients with haemochromatosis.Received for publication 17 October 1974. SubjectsFifty-two healthy adults (22 women and 30 men) were studied. In all cases the serum iron concentration was above 70 jig per dl and the transferrin saturation above 16%. Haemoglobin concentration was above 12-5 g per dl in women and 13-0 g per dl in men.Fifteen patients with primary idiopathic haemochromatosis (one woman and 14 men) were studied; all met the same haematological criteria as the normal subjects. Six of the patients were studied on two occasions giving a total of 21 observations in this group. Three patients were investigated before venesection therapy, nine during and nine after the completion of a course of venesection. Patients studied during treatment were not bled for a minimum of one month before the absorption measurement.All subjects gave their fully informed consent to the investigations. MethodsIron absorption was measured by whole body counting using a flat bed scanning technique. The whole body counter consists of four uncollimated Nal (T1) crystals 10-2 cm thick and 15-2 cm in diameter arranged symmetrically on a vertical metal ring. The subject lies on a fixed bed and the detectors traverse the entire length of the bed. The detectors are connected to a multichannel analyser with 188 on 9 May 2018 by guest. Protected by copyright.

An index of reticuloendothelial cell release of iron for erythropoiesis can be derived from simultaneous measurements of iron—dextran and transferrin‐bound iron utilization. Reticuloendothelial iron release was found to be reduced in patients with Hodgkins disease, chronic renal failure and some cases of rheumatoid arthritis. It was increased in patients with iron deficiency.

An evaluation of iron metabolism has been carried out in 23 untreated patients with Hodgkin's disease and 6 patients with other lymphomata. The reduction in red cell life span is related to the stage of the disease. There is an almost universal impairment of iron release from the reticuloendothelial system with a consequent sideropenia and failure of iron delivery to the bone marrow for erythropoiesis. This defect is found in all stages of the disease and is not related to systemic symptoms.