Analysis of heat-damaged erythrocyte clearance curves

The rate of clearance from the blood of heat-damaged erythrocytes (HDE) is used routinely as a quantitative assessment of splenic function. The time taken for the value at 3 min to fall by 50% (t0.5)is usually taken as the index of function. The clearance of HDE is dependent on three processes: splenic blood flow, splenic HDE extraction ratio and intrasplenic transit time of "unextracted' HDE, returning to the circulation. Exponential analysis of the clearance curve can resolve these three functions. Simple methods of analysis, however, such as t0.5, which are applied directly to the curve, may be weighted in favour of any one of them. In this paper, a large number of clearance curves have been analysed and the components of splenic function resolved. The t0.5, the percentage fall in HDE between 8 and 28 min (C20), the rate constant at 8 min (K8) and the rate constant of the tail of the curve (alpha 2) have been correlated with these components. K8 showed a close correlation with splenic blood flow, and alpha 2 with the rate of HDE phagocytosis. In general, the correlation between the various components of splenic function was better with C20 than with t0.5. This is explained predominantly by the fact that the t0.5 includes liver clearance. The t0.5 should therefore be used with caution as an estimate of splenic function, which can be usefully assessed by applying alternative simple methods of analysis described.