Screening for sickle cell – it’s not just about numbers

Two recent publications have looked at the frequency and distribution of sickle cell in two widely different countries, Uganda and Jamaica. At it’s simplest screening is just about numbers, how many individuals are there with sickle cell in a given population but, with the right resources and motivation, it is also about knowledge and empowerment for both governments and people.

The Uganda study was a joint investigation between Cincinnati Children’s Hospital in the USA and Makerere Hospital in Kampala. Another example of a successful collaboration between hospitals across the developed / developing world, which are becoming a distinct feature of sickle cell research. The investigators screened nearly 100,000 young children, aged between 2 to 12 months, from all over Uganda, allowing them to build up a “frequency map” for sickle cell covering the whole country.

They found that overall 13.3% of children had sickle cell trait, although the frequency varied widely across the country, with as few as 4.6% in the south-west to nearly 20% in the east-central areas.

Map showing the frequency of sickle cell trait across Uganda, with highest frequencies in the east-central regions. Pale blue - Lake Victoria to the bottom right and Lakes Albert and Edward along the western border.

Map showing the frequency of sickle cell trait across Uganda, with highest frequencies = darker colours in the east-central regions and lowest frequencies in the south-west. Pale blue = Lake Victoria in the bottom right and Lakes Albert and Edward along the western border.

The areas with the highest frequency were also those which had the greatest burden of malaria. Further evidence for the role of sickle cell trait in helping to protect young children against the most severe effects of malaria. The presence of malaria positively selects for the survival of children with sickle cell trait, so that, over time, the frequency of individuals with sickle cell trait gradually increases in those populations chronically exposed to malaria.

Frequency distribution of sickle cell trait (on left) and malaria (on right). Darker colours indicate areas with highest frequencies.

Frequency distribution of sickle cell trait (on left) and malaria (on right). Darker colours indicate areas with highest frequencies. The frequency of malaria and sickle cell trait almost exactly match each other.

For sickle cell disease, as opposed to sickle cell trait, the average frequency was 0.8%, varying between 0.5 and 1.5%. The latter figure is remarkable implying that 1 to 2 children in every 100 will have sickle cell disease in east-central Uganda. Interestingly, the frequency of sickle cell disease in all areas of the country was lower in the older age groups, confirming that young babies with sickle cell disease have a very high early mortality.

Using their data the investigators calculated that approximately 15,000 babies are born every year with sickle cell disease in Uganda, with the birth rate varying in different parts of the country. This is very basic information, but for governments attempting to develop policies to address the specific health needs of their population, it is absolutely essential.

Burden of sickle cell trait and disease in the Uganda Sickle Surveillance Study (US3): a cross-sectional study. Grace Ndeezi, Charles Kiyaga, Arielle G Hernandez, Deogratias Munube, Thad A Howard, Isaac Ssewanyana, Jesca Nsungwa, Sarah Kiguli, Christopher M Ndugwa, Russell E Ware, Jane R Aceng. Lancet Global Health (2016); volume 4, pages e195-200.   http://dx.doi.org/10.1016/ S2214-109X(15)00288-0

Screening for sickle cell has a long history on the island of Jamaica. It was a screening programme of over 100,000 consecutive deliveries in Kingston, between 1973 and 1981, that identified the Jamaican Cohort, a group of children with sickle cell disease, who have been followed throughout their lives. Much has been learnt from the cohort about the natural history of sickle cell disease and about how to intervene effectively to keep people well and healthy.

The latest screening exercise was carried out in the Parish of Manchester and was a response to a demand from college students to be told their sickle cell type.

jamaica-political-map-1

Manchester Parish is on the south coast of Jamaica between St Elizabeth and Clarendon. Main town Mandeville.

The investigators screened 16,636 students aged between 15 and 19 years over a 6 year period (2007-2013). The students gave informed consent, completed a short health questionnaire and then gave a blood sample. After the analysis of their blood was complete each student was given a laminated card specifying their haemoglobin type. Those with sickle cell trait, or any other haemoglobinopathy, were given appropriate counselling, information and support. The aim was to identify all those with sickle cell trait, haemoglobin C trait and beta thalassaemia trait, as well as any more unusual types of haemoglobin. At the end of the study the take up rate was 92%, a reflection of the motivation and enthusiasm of the students.

The frequency figures were broadly similar to the results of previous surveys. Sickle cell trait occurred in 9.6% of teenagers, Hb C trait in 3.5% and beta thalassaemia trait in 0.9%. The frequency of sickle cell disease was as predicted, with a birth rate for Hb SS disease of 1 in every 300 births and for Hb SC disease 1 in every 500 births.

More important than the figures however, was the fact that the study was driven by the demand of young people to know their sickle cell status and that the massive logistical problems of screening and counselling such large numbers were successfully overcome. The key question is one of empowerment; now that they have this information will this alter the young peoples choice of life partners, reducing the birth rate of babies with sickle cell disease? The investigators plan to start a long term screening programme of all births in the same locality to answer this question in the future.

It is often claimed that these sorts of screening programmes are too difficult and costly to undertake, the reason why they have never been implemented in areas of the USA and UK where there are many people with sickle cell trait. This study shows, on the contrary, that such programmes are feasible and, by providing the right information at the right time, allows individuals to make informed reproductive choices.

Haemoglobin variant screening in Jamaica: meeting student’s request. Karlene Mason, Felicea Gibson, Douglas Higgs, Chris Fisher, Swee L Thein, Barnaby Clark, Andreas Kulozik, Margit Happich, Beryl Serjeant and Graham Serjeant. British Journal of Haematology (2016); volume 172, pages 634-635.   doi:10.1111/bjh.13531

For a discussion by Professor Graham Serjeant about the background to the project see:   http://jamaica-gleaner.com/gleaner/20110116/focus/focus5.html

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About rogerjamos

I am a consultant haematologist who has worked in Hackney, London, UK with patients who have sickle cell disease for many years. Knowledge is power; the hope is that this blog will empower patients by putting them in touch with contemporary research into sickle cell disease and facilitating informed discussion on the issues raised. Dr Roger Amos MA, MD, FRCPath
This entry was posted in global burden of disease, screening, sickle cell carrier, sickle cell disease, sickle cell trait and tagged , , , , . Bookmark the permalink.

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