Optimal haematocrit in subjects with normal haemoglobin genotype (HbAA), sickle cell trait (HbAS), and homozygous sickle cell disease (HbSS).

The determination of an optimal haematocrit (H0) has important clinical implications if such a level can be attained, and more importantly, maintained. This is defined as a haematocrit level, above or below which oxygen delivery is deleteriously affected. This study is designed to determine an optimal haematocrit in normal (AA), sickle cell trait (AS) and sickle cell disease (SS) subjects. Twenty-seven apparently healthy subjects having normal haemoglobin genotype, 24 with sickle cell trait and 42 with homozygous sickle cell disease were recruited into the study. Whole blood viscosity (WBV) was measured by a Wells Brookfield Cone and Plate Viscometer at a shear rate of 230 sec-1. Haematocrit was determined by an AC.Tron Coulter Counter. The optimal haematocrit was calculated as the inverse of a constant, K, which was derived from the haematocrit and viscosity data. Our findings showed that the H0 varied significantly among the 3 haemoglobin genotypes, in the order AA vs SS and AS vs SS. Additionally, the data indicated an increased H0 in subjects with sickle cell trait, suggesting a possible impairment in oxygen delivery in these individuals.

Oxygen delivery index in homozygous sickle cell disease: steady and crisis states.

One of the common complications of sickle cell disease is the vaso-occlusive crisis or sickle cell crisis which could result in impaired oxygen delivery to the tissues. This study investigates the oxygen delivery index (ODI) in 38 patients with homozygous sickle cell anaemia. Thirty-three patients were in the steady state and five were experiencing crisis at the time of recruitment. Whole blood viscosity was measured with a Wells Brookfield viscometer at a shear rate of 230 sec(-1) and haematocrit was measured with an AC Tron Coulter Counter. The ODI, which is an indirect measure of the capacity of blood to deliver oxygen to tissues, was calculated as the ratio of haematocrit to whole blood viscosity values. There was no statistically significant difference in the ODI between the steady and crisis states, suggesting that tissue oxygenation is not the only factor involved in the sickle cell crisis.

Oxygen delivery index in subjects with normal haemoglobin (HbAA), sickle cell trait (HbAS) and homozygous sickle cell disease (HbSS).

Sickle cell disease is characterized by altered blood rheology due to a reduced haematocrit and a resulting lowered viscosity. Oxygen carriage, and consequently oxygen delivery, may be deleteriously affected if the haematocrit reduction is such as to limit oxygen uptake from the lungs and delivery to the tissues. The present study seeks to determine and compare the oxygen delivery index (ODI) in subjects with normal and abnormal haemoglobin genotypes. Thirty four apparently healthy subjects having normal haemoglobin genotype (AA), 27 with sickle cell trait (AS) and 50 with homozygous sickle cell disease (SS) were recruited into the study. Whole blood viscosity was measured at low and high shear rates of 23 s(-1) and 230 s(-1), respectively, using a Wells Brookfield Cone and Plate Viscometer. Haematocrit was determined using an AC.Tron Coulter Counter. The oxygen delivery index was calculated as the ratio of the haematocrit to whole blood viscosity. There was a statistically significant difference in the ODI in the SS group compared with both the AA and AS groups. There was no statistical significance in the ODI between the AA and AS groups. The ODI may be considered as a useful assessment of oxygen delivery in subjects with sickle cell disease.