1 Sensitisation of school communities by meetings of all relevant groups including Parent
-Teachers Associations (PTA), principals, school nurses, guidance counsellors and pupils.
2 Circulating information to parents and requesting written refusal for non-participation of
their child if desired.
3 Illustrated lectures on sickle cell disease and its prevent given by the Sickle Cell Trust.
4 Logistics of screening process
i) Obtain 4th form class lists and generate preprinted labels.
ii) During pre-arranged visits, students complete data forms with demographic information, blood tubes are labelled, and venepunctures performed by team of 3-4 phlebotomists who can bleed up to 230 students in 2 hours.
iii) Attendances checked against class registers identifying defaulting students for future sits – larger schools may require 3-5 visits.
5 Blood samples are taken by venepuncture in the school environment.
6 Samples are analysed in the Sickle Cell Trust laboratory in Mandeville.
7 Permanent laminated genotype cards (82x53mm) are produced, distributed to the students and carriers of abnormal genes are offered counselling.
6 Samples are analysed in the Sickle Cell Trust laboratory in Mandeville.
7 Permanent laminated genotype cards (82x53mm) are produced, distributed to the students and carriers of abnormal genes are offered counselling.
Text on cards
AA Normal. You are not at risk of having a child with sickle cell disease. AS Sickle cell trait. This will not affect your health but you could pass it on to your children. If your partner is normal, you cannot have a child with sickle cell disease. See other side for further details. AC HbC trait and Abth Beta thalassaemia trait – messages similar to above.
Sample Collection and Coverage
School Screening in the 6 years of the Programme
For the academic year 2007/8 screening did not start until January 2008 resulting in fewer students but screening in the last 5 years exceeded 2,600 students annually.
Compliance with Testing in 14 Schools over Screening Period
Overall compliance with testing rose steadily from 56% in the first year to 92% in the last year. The real compliance is greater since the denominator will be reduced by students leaving school without notification.
Performance of Individual Schools Bracketed figures indicate number of school visits.
Gender as Determinant of Screening Female students were more likely to be screened although the gender inequality improved over the first 3 years (see below). This apparent gender inequality requires cautious interpretation since girls predominated in some schools.
Laboratory Analysis
Samples are sorted against a computerized database and ID numbers allocated.
An automated haematology analyser gives red cell indices. An MCH ≤ 26pg suggests beta thalassaemia trait.
Alkaline haemoglobin electrophoresis detects HbS, HbC, and other variants.
The slide sickle test confirms the identity of HbS
Beta thalassaemia trait is suspected with an MCH ≤ 26pg and an RDW < 18, supported by HbA2 values ≥ 3.5% on HPLC (above) and confirmed by molecular studies.
Results of School Screening
a) Haemoglobin Genotypes
Distribution of Genotypes by Year
Haemoglobin Genotypes
- The sickle cell trait in 9.66% and HbC trait in 3.43% are similar rates to those observed in the Jamaican Cohort Study (10.05% and 3.59% respectively).
- HbC is a gene of West African ancestry which may be inherited from both parents producing CC disease or with beta thalassaemia producing C beta thalassaemia, both being mild conditions.
- Beta thalassaemia trait may have been underestimated in the first 2 years because of a relatively inaccurate method for measuring HbA2 and a more accurate prevalence of 0.90 was obtained in the last 4 years.
- Sickle cell-beta+ thalassaemia (S beta+ thal.) or the more severe sickle cell-betao thalassaemia (S betao thal.).
- HPFH (hereditary persistence of fetal haemoglobin) is a mild genetic abnormality which does not give rise to sickle cell disease but the observed prevalence is 20 times higher than that reported among Afro-Americans. Combined with HbS, S-HPFH electrophoretically resembles SS disease but is entirely benign with normal haemoglobin levels.
- Variants are uncommon abnormalities of haemoglobin, all are asymptomatic as traits but some are clinically significant when inherited with HbS.
- SS disease occurs once in every 300 births and SC disease once in every 500 births in Jamaica so the anticipated numbers born in a population of 15,593 should be 52 SS and 31 SC; the observed figures of 23 and 34 indicate no losses of persons with SC disease but that over half of SS persons failed to enter the screened population either from early death, failure to enter the school population or to attend on the screening day, or possibly knowing their genotype did not feel that additional confirmation was needed.
In conclusion, 2269 or 14.6% of the students carried genes which could result in a baby with sickle cell disease.
b) Molecular Mutations
i) Beta thalassaemia mutations (n=122)
Data courtesy of Dr. Andreas Kulozik & colleagues, University of Heidelburg, Germany
ii) Rare haemoglobin variants (15 identified to date)
Data courtesy of Prof. Doug Higgs & Dr. Chris Fisher, University of Oxford, UK
ii) Hereditary Persistence of Fetal Haemoglobin (HPFH) - 44 identified to date
Data courtesy of Prof. Swee Lay Thein & colleagues, King’s College Hospital, London.
c) Iron Deficiency Anaemia
An unexpected finding resulting from the need for full haematology was the frequency of haemoglobin levels < 10 g/dl in 301 students (279 or 92.7% female). The female preponderance and the low mean red cell volume are both consistent with iron deficiency (see table below) as is the striking response in haemoglobin level to iron supplementation. The overall prevalence of serious anaemia was 3.2% of all females and 0.3% of all males. All students with iron deficient indices were interviewed regarding diet, advised to take worm medicine and were offered oral iron supplementation, often with striking improvement in their indices. Of 46 students observed in one year, the average haemoglobin increase was 2.75g (range -0.2 to +6.6) the poor responders generally failing to take the treatment.
