An Improved Osmotic Fragility Protocol for Screening of Beta Thalassaemia Carriers in Remote and Resource Limited Settings

Abstract

Introduction: In a vast country like India where beta thalassaemia is a health burden and majority of the population reside in rural regions, a simple and economic primary screening test is vital. Aim: To modify the existing Naked Eye Single Tube Red Cell Osmotic Fragility Test (NESTROFT) to increase it’s sensitivity. Materials and Methods: A 3.6% stock buffer containing HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) was compared with one without HEPES over a period of 6 months. The working buffers (0.36%) were freshly prepared by a 1:10 dilution using HPLC grade water. One hundred fifty seven individuals were tested which included normal individuals, beta thalassaemia carriers and HbS carriers. Results: The solution containing HEPES picked up all the beta thalassaemia carriers and had a sensitivity of 100%, specificity of 79.22%, positive predictive value of 80.95% and negative predictive value of 100% for detection of beta thalassaemia carriers. The standard buffer without HEPES missed 3 beta thalassaemia carriers and had a sensitivity of 95.59%, specificity of 74.03%, positive predictive value of 76.47% and negative predictive value of 95.0%. The pH of the stock solution containing HEPES remained stable for 150 days as compared to one without HEPES. All the HbS carriers were also picked up with the former buffer while 4 of them were missed with the standard buffer. Conclusion: In remote and resource limited settings NESTROFT is a valid first line screening test for beta thalassaemia carriers. We have been able to improve its sensitivity and negative predictive value by using a modified solution which is stable for a longer period.

Keywords

• community screening
• modified nestroft
• rural regions