Background
The persistent high prevalence of anaemia among Indian women of reproductive age (WRA) despite aggressive long-term iron supplementation could be related to over-diagnosis from an inappropriately high haemoglobin (Hb) diagnostic cut-off. To develop an appropriate cut-off for Indian WRA, we hypothesized that during iron-folic acid (IFA) supplementation to a mixed (anaemic/non-anaemic) WRA population, the positive slope of the Hb-plasma ferritin (PF) response in anaemic women would inflect into a plateau (zero-response) as a non-anaemic status is reached. The 2.5th percentile of the Hb distribution at this inflection point will be the diagnostic Hb cut-off for iron-responsive anaemia. Method: A hierarchical mixed effects model, with a polynomial mean and variance model to account for intraclass correlation due to repeated measures, was used to estimate the response curve of Hb to PF, or body iron stores, in anaemic and non-anaemic WRA (without inflammation), who were receiving a 90-day IFA supplementation.
Conclusion
The derived Hb cut-off is lower than the current adult values of 12 g/dL and could partly explain the persistently high prevalence of anaemia.
Results
The Hb response curve at low PF values showed a steep increase, which inflected into a plateau at a PF of 10.1 µg/L and attained a steady state at a PF of 20.6 µg/L. The Hb distribution at the inflection was a normal probability distribution, with a mean of 12.3 g/dL. The 2.5th percentile value of this distribution, or the putative diagnostic Hb cut-off for anaemia, was 10.8 g/dL (~11 g/dL).