Sickle cell disease: diagnosis and health maintenance: SAQ

This boy has sickle cell anaemia, the HbSS genotype, found on newborn screening before he has been ill at all. The haemoglobin pattern of FS on high-performance liquid chromatography, with haemoglobin F and haemoglobin S and little or no haemoglobin A, is the classic pattern of HbSS in the newborn, and the repeat test confirms it. The newborn is well because fetal haemoglobin protects the cell, and the complications begin only as the fetal haemoglobin falls through the first year. The task now is to keep him well. [5]

Question 1 (10 marks)

Outline the diagnosis and the immediate health-maintenance plan for this eight-week-old boy, justifying each step with the relevant evidence. [5]

A full-mark answer addresses the genetic diagnosis, the penicillin prophylaxis with exact doses, the immunisation plan, the parental education, and the timing of the next interventions. [5]

Diagnosis and counselling (2 marks). The FS pattern on high-performance liquid chromatography is diagnostic of HbSS, confirmed on repeat testing, and no further test is needed unless the result is ambiguous, in which case deoxyribonucleic acid testing of the HBB gene settles the mutation. The disease is autosomal recessive, the p.Glu6Val substitution, and two carrier parents have a one in four chance in each pregnancy, so the family is counselled on the inheritance and the option of testing the siblings and future pregnancies. [5]

Penicillin prophylaxis (3 marks). Penicillin V prophylaxis is the single most important early intervention, and the PROPS trial of Gaston and colleagues showed it reduced pneumococcal sepsis by 84 percent. It is started by two months of age, which is now, and the dose is 125 mg orally twice daily under three years of age, continued to five years. The parents are taught that any fever above 38.5 degrees Celsius is an emergency that needs prompt assessment and a parenteral antibiotic such as ceftriaxone, because the child develops functional asplenia in the first years of life. [1][5]

Immunisation (2 marks). The routine childhood immunisations are given, and on top of them the encapsulated-organ cover: the pneumococcal conjugate vaccine on schedule plus the 23-valent polysaccharide vaccine at two years and again five years later, the meningococcal ACWY and serogroup B vaccines, Haemophilus influenzae type b, and the annual influenza vaccine. The parents are taught to palpate the spleen and to bring the boy in at once for pallor, lethargy, or a rapidly enlarging spleen, the signs of acute splenic sequestration. [5]

Future interventions and counselling (3 marks). Hydroxyurea is offered from nine months of age at a starting dose of 20 mg per kg per day, regardless of severity, with a full blood count every four weeks. The annual transcranial Doppler begins at two years and runs to sixteen, with chronic transfusion to keep the haemoglobin S under 30 percent if the velocity reaches 200 cm per second or more. The family is enrolled in the sickle cell clinic, given a written emergency plan, and the parents are reminded that with this package the boy can expect to reach adulthood. [2][3]