SCD denotes all genotypes containing at least one sickle gene, in which HbS makes up at least half of the hemoglobin present. Major sickle genotypes described so far include:

• HbSS disease or sickle cell anemia (the most common form): Homozygote for the S globin with usually a severe or moderately severe phenotype and with the shortest survival

• HbS/b-0 thalassemia: Double heterozygote for HbS and b-0 thalassemia; clinically indistinguishable from sickle cell anemia (SCA)

• HbS/b+ thalassemia: Mild-to-moderate severity with variability in different ethnicities

• HbSC disease: Double heterozygote for HbS and HbC characterized by moderate clinical severity

• HbS/hereditary persistence of fetal Hb (S/HPHP): Very mild or asymptomatic phenotype

• HbS/HbE syndrome: Very rare, with a phenotype usually similar to HbS/b+ thalassemia

• Rare combinations of HbS with other abnormal hemoglobins such as HbD Los Angeles, G-Philadelphia, HbO Arab, and others

For more on the types of SCD, read here.

Although hematologic changes indicative of the disorder are evident as early as the age of 10 weeks, clinical characteristics of SCD generally do not appear until the second half of the first year of life, when fetal Hb levels decline sufficiently for abnormalities caused by HbS to manifest. SCD then persists for the entire lifespan. After age 10 years, rates of painful crises decrease, but rates of complications increase.

For more on the epidemiology of SCD, read here.

The most common clinical manifestation of SCD is vaso-occlusive crisis. A vaso-occlusive crisis occurs when the microcirculation is obstructed by sickled red blood cells, causing ischemic injury to the organ supplied and resultant pain. Pain crises constitute the most distinguishing clinical feature of SCD and are the leading cause of emergency department visits and hospitalizations for affected patients.

For more on presentation of SCD, read here.

Obtaining a series of baseline values on each patient to compare with those at times of acute illness is useful. The table below shows a typical schedule of routine clinical laboratory evaluations.

For more on the workup of SCD, read here.

Transfusions are not needed for the usual anemia or episodes of pain associated with SCD. Urgent replacement of blood is often required for sudden, severe anemia due to acute splenic sequestration, parvovirus B19 infection, or hyperhemolytic crises. Transfusion is helpful in acute chest syndrome, perioperatively, and during pregnancy.

For more the treatment of SCD manifestations, read here.

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Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.

Cite this article: Emmanuel C. Besa. Quiz: Are You Prepared to Confront Sickle Cell Disease? Medscape. Feb 18, 2016.