A novel method for calculating mean erythrocyte age using erythrocyte creatine

Estimating the lifespan of erythrocytes is useful for the differential diagnosis of anemia. However, measuring the lifespan of erythrocytes was very difficult; therefore, it was seldom measured. Erythrocyte creatine (EC) decreases reflecting erythrocyte age. We developed a method to obtain mean erythrocyte age (M(RBC)) from EC. We reanalyzed the previously published data from 21 patients with hemolytic anemia, which included EC and the half-life of (51)Cr. M(RBC) and log(e) EC showed excellent significant linearity (r = −0.9475, p < 0.001), proving that it could be treated as a mono-exponential relationship within the studied range (EC: 1.45 – 11.76 μmol/g Hb). We established an equation to obtain M(RBC) (days) from EC (μmol/g Hb): M(RBC) = −22.84log(e) EC + 65.83. This equation allowed calculation of M(RBC) based on EC which has practical applications such as the diagnosis of anemia.