How sickle cell disease is tested on Step 1
Mutation, mechanism, and complications.
Complications
Most complications come from vaso-occlusion or hemolysis.
Infections and the spleen
Repeated infarction leaves a small, fibrotic spleen.
- Encapsulated bacteria: Streptococcus pneumoniae, Haemophilus influenzae type b, Neisseria meningitidis; give vaccines and penicillin prophylaxis in early childhood.
- Osteomyelitis: Salmonella is classic; Staphylococcus aureus is still common.
- Smear: sickle cells, target cells, and Howell-Jolly bodies (nuclear remnants normally removed by the spleen).
Diagnosis and treatment
Confirm with electrophoresis; prevent crises and infection.
| Step | Details |
|---|---|
| Diagnosis | Newborn screening; hemoglobin electrophoresis or HPLC |
| Hydroxyurea | Raises HbF, reduces crises and acute chest syndrome; causes myelosuppression |
| Infection prevention | Pneumococcal and other vaccines; penicillin prophylaxis in young children |
| Transfusion | Stroke prevention and severe crises; risk of iron overload |
| Other | Folic acid; L-glutamine; crizanlizumab; stem cell transplant and gene therapy |
HbC (glutamate → lysine) causes a milder hemolytic anemia; HbSC disease is milder than HbSS.
Worked example
Use the reticulocyte count.
functions Worked example — a sudden drop in hemoglobin
A 9-year-old with sickle cell disease has fatigue and pallor a week after a fever and a "slapped cheek" rash in a sibling. Hemoglobin is 4.5 g/dL (baseline 8), the spleen is not enlarged, and the reticulocyte count is near zero. What is the cause?
- Hemoglobin has fallen far below baseline.
- A normal-sized spleen argues against splenic sequestration.
- Near-zero reticulocytes mean the marrow has stopped making red cells.
- Parvovirus B19 infects erythroid precursors; in chronic hemolysis this causes an aplastic crisis.
Answer. Aplastic crisis from parvovirus B19; supportive transfusion.