Simple in vivo bioassay for erythropoietin

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Abstract
A new method of in vivo bioassay for erythropoietin (EPO) is described. This method is based on the measurement of immature reticulocytes in EPO‐treated mice using an automatic microcell counter, and is simpler and more precise than the existing methods of polycythaemic mouse assay and starved rat assay. Normal mice were injected subcutaneously for 3 successive days with EPO at the doses betweeen 0 and 9·6 IU/mouse. On the following day, 20 μl of peripheral blood from each EPO‐treated mouse was collected and haemolysed with a stromatolysing agent, Quicklyser. Residual particles derived from immature reticulocytes in the stromatolysed blood cells were counted using a microcell counter (Sysmex CC‐180A) and a cell monitor (Sysmex CM‐5). The number of the residual particles increased in a dose‐dependent manner in EPO‐treated mice. The mean of correlation coefficients of five log dose‐response lines was 0·924, and the mean of precision indices was 0·138. A good correlation was also observed between the residual particle counts and reticulocyte counts obtained from smears.