The England-Fraser formula is intended to help in distinguishing between thalassemia and other causes of microcytosis.
England-Fraser formula =
= ((MCV) - ((5 * (hemoglobin)) + (RBC) + K))
where:
• MCV is the mean corpuscular volume as measured in femtoliters
• hemoglobin is in g/dL
• RBC is the number of red blood cells per µL, divided by 10^6
• K = 3.4 if the hematocrit is corrected for plasma trapping (usual situation) or 8.4 if it is not.
Interpretation:
• no differentiation: formula > 0 (positive)
• thalassemia minor: formula < 0 (negative)
• If the hemoglobin electrophoresis is normal and England-Fraser result negative in the absence of iron deficiency, then alpha thalassemia minor likely.
Limitations:
• The England-Fraser formula may provide only poor discrimination between thalassemia and non-thalassemic causes of microcytosis.
• In patients with polycythemia vera who develop iron deficiency, a negative value for the England-Fraser formula may result.
• The validity of the discriminant function may depend on the relative proportions of patients with iron-deficiency anemia and thalassemia in the population being examined.
