Thalassaemia and haemoglobinopathy in the Waikato and Bay of Plenty: A review of testing and prevalence of haemoglobinopathy at Pathlab Waikato

Abstract

Haemoglobinopathies are amongst the most common genetic disorders in the world but remain relatively overlooked. The World Health Organisation estimates around 5.2% of the global population may be carriers of a pathogenic haemoglobinopathy due to a mutation in one of the haemoglobin genes. For the past decade Pathlab Waikato has established a database of all diagnosed haemoglobinopathy and thalassaemia, with the intention that this data may be used to assess and improve the New Zealand national screening service. The purpose of this research was to analyse this database to investigate 1) What is being diagnosed in our region? 2) How common are these haemoglobinopathies? and 3) What is being missed? Answers to this will provide a better understanding of the pathology and prevalence of this disease in our region, and to provide recommendations and strategy for future testing.

The haemoglobinopathy database was analysed alongside data from incidental abnormal haemoglobin detection through testing for HbA1c. This information was run through RStudio for statistical analysis of ethnicity data to confirm that ethnicity was a significant predictor of the presence of abnormal haemoglobin (p value <0.001). Prevalence of different haemoglobinopathies was calculated and this was compared to previously reported prevalence both globally and within certain ethnic groups. Using population information from StatsNZ and the past three New Zealand Censuses (2023, 2018, 2013) the ethnic makeup of our testing population was also determined. With all of this information combined, differences and shortfalls in our database can be identified when compared to calculated estimates of prevalence of abnormal haemoglobin.

From the database, Pathlab performed 6,589 thalassaemia screens with a positive detection rate average of 53% with a steady increase in haemoglobinopathy testing every year. The most commonly diagnosed haemoglobinopathies (in order) were α thalassaemia, β thalassaemia, heterozygous HbE, and heterozygous HbS. Using known ethnic prevalence from the literature review and the ethnic makeup of our community from the census, it was found we are detecting less than what would be expected for our population. For example, 5.85% of our population has identified themselves as Indian, and based on previous reports at least 3% of them should be carriers for β thalassaemia. This would come to roughly 1,179 people. However, during our screening period, only 621 confirmed diagnoses of β thalassaemia were made. Furthermore, using the Hardy-Weinberg equation, it is estimated there may be over 10,000 and 3,000 carriers of HbE and HbS, respectively. This is compared to only 358 and 171 detected in our database. Even if the actual allele frequency is half of what was calculated, the shortfall is stark.

With all this in mind, Pathlab are already introducing an extra step through the screening of abnormalities found incidentally in HbA1c. However, there are further steps we can take to tackle this deficit, including the establishment of a national database and national screening service. The process to allow accurate haemoglobinopathy screening in New Zealand was outlined. If haemoglobinopathy screening was introduced as part of an antenatal screen, it would help to bridge the gap we have uncovered here to prevent negative health outcomes and further strain on our health care system.