The utility of Reticulocyte Haemoglobin (Ret-He) for iron deficiency screening at Canterbury Health Laboratory : a thesis presented to the Massey University College of Health in partial fulfilment of the requirements for the Master of Health Science specializing in Medical Laboratory Research at Massey University, New Zealand

Abstract

Background: Iron deficiency (ID) is the most common nutritional deficiency worldwide and is the commonest cause of anaemia. Diagnosis of iron deficiency has traditionally been based on Biochemistry parameters such as Ferritin, total-iron binding capacity (TIBC), and Transferrin saturation. However, recent laboratory practices around the world have established that Reticulocyte Haemoglobin (Ret-He) is as a superior indicator of iron deficiency compared to the classical methods. Ret He is a laboratory parameter that can be determined using automated haematology analysers. It is a measurement of haemoglobin of reticulocytes and provides a rapid and reliable measure of the functional iron available for the process of erythropoiesis. Thus, measuring Ret-He provides information about iron status change in the body much earlier compared to the measurement of ferritin. Ret-He is not affected by inflammation and is more reliable for iron studies compared to ferritin during inflammatory states of the body. Aim: This study aimed to establish a normal reference interval for Ret-He and use sensitivity and specificity calculations to determine an optimum cut-off of Ret-He for determination of ID and IDA. Methods: Reference intervals for Ret-He were calculated from 50 normal blood samples using +/-2SD from mean. 321 blood samples with existing Complete Blood Count (CBC) and iron studies tests were selected for retrospective Ret-He analysis in Sysmex XN-20 haematology analyser. Results of Ret-He, haemoglobin and ferritin were compared against each other. Sensitivities and specificities of Ret-He at different levels were calculated for ID and IDA using Chi square and 2x2 box plot. Receiver operating characteristic curve analysis, calculation of area under the curve with 95% confidence intervals and Youden’s Index calculations were performed to decide the optimum cut-off of Ret-He for ID and IDA. Results: The reference interval for Ret-He was calculated to be 32.4 -37.5 pg. Based on the ROC curve analysis and Youden’s index calculation using the specificity and sensitivity values of Ret-He, an optimum value of 34 pg and 24 pg was calculated for diagnosis of ID and IDA respectively. Ret-He levels in IDA were decreased in comparison with non-IDA population of both sexes and the difference was statistically significant. Ret-He levels were reduced in a number of patients with raised CRP who had normal or high ferritin results. Conclusion: Ret-He is a cost-effective rapid response laboratory parameter that can be a valuable iron studies tool. Addition of Ret-He test to routine haematology tests such as CBC and Reticulocyte can add diagnostic value for screening and diagnosis of ID and IDA respectively. Ret-He is particularly valuable in inflammatory states of patients where ferritin results may not be reliable. Ret-He is not a substitution for existing iron studies tests like ferritin but is an additional tool with valuable clinical utility.