Z score analysis: A novel approach to interpretation of an erythrogram

ABSTRACT

Context Z score defines the shift of an observed value from the mean. Aims: By determining the direction of this shift and its absolute value for mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC), one can quickly screen the hemogram for any spurious results in RBC parameters and also predict the type of anemia. This is because MCH and MCHC are derived parameters (from Hb, RBC, MCV) and thereby reflect the true as well as false changes in an erythrogram. Materials and Methods: A total of 975 hemograms were studied retrospectively. Basic statistical formulae using mean and standard deviation were applied to calculate z scores for MCH and MCHC. Results obtained were compared with the standard method and validated by an independent cohort of 100 random samples run on a different machine. Results and Statistical Analysis: Z score was found to be statistically significant (p <.001) in diagnosing iron deficiency anemias, megaloblastic anemias, hemolytic anemias, regenerative anemias, anemia of chronic disease and spurious findings. Z score was not significant (p = 0.9) in predicting beta thalassemia trait. The sensitivity was low for the differentials of microcytic hypochromic anemias. Conclusions: Despite this, Z score can be of immense help to the clinicians and pathologists in making quick interpretation of the underlying red cell abnormalities. Also, it can be used as a quality assessment tool in hematology laboratories taking pre analytical and analytical factors into account.