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 (MRBC) from EC.

We reanalyzed the previously published data from 21 patients with hemolytic anemia, which included EC and the half-life of 51Cr.

MRBC and loge 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 MRBC (days) from EC (μmol/g Hb): MRBC = −22.84loge EC + 65.83.

This equation allowed calculation of MRBC based on EC which has practical applications such as the diagnosis of anemia.