New diagnostic parameters or indexes for detection of absolute iron deficiency, latent iron deficiency, functional iron deficiency, or latent functional iron deficiency have been disclosed. The parameters include a RBC size factor, RSf.sub.1 defined by the formula of (MCV.times.MRV).sup.1/2, or RSf.sub.2 defined by the formula of (MCV.times.MRV)/100, a volume-hemoglobin factor (VHf) defined by the formula of (MCV.times.Hgb)/100, and a volume-hemoglobin/distribution factor (VHDWf) defined by the formula of (MCV.times.Hgb)/(RDW.times.10). Further disclosed are the methods of using these parameters for detection of absolute iron deficiency, latent iron deficiency, functional iron deficiency, or latent functional iron deficiency. Also disclosed is a method of using RSf for detection of hemochromatosis.