A 10-month-old boy is brought to the clinic by his mother due to irritability and swelling of both hands. She notes that he has been crying more than usual for the past two days and appears to be in pain when the hands are touched. His birth history was unremarkable, and he has been meeting developmental milestones. All vaccines are up to date. He is febrile at 38.3°C (100.1°F). On physical examination, there is symmetric, non-pitting edema and erythema of the dorsal aspects of both hands. Laboratory studies reveal a hemoglobin of 7.4 g/dL, mean corpuscular volume (MCV) of 82 fL, and a reticulocyte count of 8%.
Which of the following hemoglobin electrophoresis patterns is most likely to be found in this patient?
The correct answer is:
A) HbA: 0%, HbS: 85%, HbF: 15%
This patient is presenting with dactylitis (painful swelling of the hands or feet), which is a classic early manifestation of sickle cell disease (HbSS) in infants. The condition is caused by the sickling of red blood cells leading to vaso-occlusion in the small bones of the hands and feet. The lab results confirm an anemia with an appropriate reticulocytosis, indicating a hemolytic process. In a patient with homozygous sickle cell disease, the gene mutation replaces glutamic acid with valine at the sixth position of the beta-globin chain. Consequently, there is an absence of normal adult hemoglobin (HbA), because the patient cannot produce normal beta-globin chains. The electrophoresis will show a complete lack of HbA, a predominance of HbS, and a varying percentage of fetal hemoglobin (HbF), which persists longer in these patients to compensate for the lack of functional adult hemoglobin.
Answer choice B: HbA: 60%, HbS: 40%, HbA2: <3.5%, is incorrect. This pattern is characteristic of sickle cell trait (HbAS). Individuals with sickle cell trait are typically asymptomatic and do not develop dactylitis or hemolytic anemia, as they have sufficient functional HbA to prevent sickling under normal physiological conditions.
Answer choice C: HbA: 90%, HbA2: 6%, HbF: 4%, is incorrect. This pattern shows an elevated HbA2 (normal is typically 1.5–3.5%), which is the diagnostic hallmark of beta-thalassemia trait. While beta-thalassemia trait presents with microcytic anemia, it does not cause dactylitis or the severe hemolytic picture seen in this infant.
Answer choice D: HbA: 95%, HbH: 5%, is incorrect. The presence of HbH indicates HbH disease, a form of alpha-thalassemia where three of the four alpha-globin genes are deleted. HbH disease usually presents with chronic hemolytic anemia and mild splenomegaly, not the painful vaso-occlusive crises associated with sickle cell disease.
Answer choice E: HbA: 98%, HbA2: 2%, HbF: <1%, is incorrect. This is the electrophoresis pattern of a healthy individual without any hemoglobinopathy. Given the patient’s clinical presentation of anemia, reticulocytosis, and dactylitis, this result is impossible.
Key Learning Point
Sickle cell disease (HbSS) is the homozygous form of the condition and is characterized by the absence of HbA on electrophoresis and the presence of HbS. Dactylitis is a classic, early pain crisis presentation in infants aged 6 months to 2 years, often presenting as the initial clinical sign that leads to the diagnosis.
