40 Sickle Cell (Hemoglobin SS) Disease

Michelle To and Valentin Villatoro

Cause(s):

β globin chain amino acid substitution in the 6th position from glutamic acid (Glu) to valine (Val). In the homozygous form of the disease, both β globin genes are affected.1

 

Inheritance:

Autosomal dominant2

 

Demographics:3

Tropical Africa

Mediterranean Areas

 

Sickle cell disease is common in areas where malaria is prominent and it is suggested that the disease acts as a protective factor for malaria. This protection is only seen in heterozygotes, as homozygotes often lose splenic function, which is essential for combating the parasite.

 

Cellular Features:1-4

See sickle cell (drepanocytes) under RBC morphology for more information about cell formation.

 

The formation of sickle cells becomes irreversible over time leading to the formation of rigid and “sticky” sickle cell aggregates resulting in many complications.

 

Complications:1-4

Chronic hemolytic anemia

Vaso-occlusion (can lead to ischemic tissue injury, splenic sequestration of RBCs, autosplenectomy)

Prone to infections

Nephropathies

Stroke

 

Laboratory Features of Sickle Cell Disease:2-4 

CBC:

RBC: Decreased

WBC: Increased

PLT: Increased

Hb: Decreased

RETIC: Increased

RDW: Increased

PBS:

Sickle cells

Normochromic, normocytic RBCs

Target cells

Polychromasia

nRBCs

Howell-Jolly bodies

Pappenheimer bodies

Basophilic Stippling

BM:

Erythroid Hyperplasia

Iron stores: often increased

Hemoglobin Electrophoresis:

Hb S: 80-95%

Hb A: None

Hb A2: 2-%

Hb F: 5-20%

Other Tests:

Solubility Screen: Positive

Metasulfite Sickling Test: Positive

HPLC

Hemoglobin Electrophoresis


References:

1. Chonat S, Quinn CT. Current standards of care and long term outcomes for thalassemia and sickle cell disease. Adv Exp Med Biol [Internet]. 2017 [cited 2018 Jun 5];1013:59–87. Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5720159/

1. Randolph TR. Hemoglobinopathies (structural defects in hemoglobin). In: Rodak’s hematology clinical applications and principles. 5th ed. St. Louis, Missouri: Saunders; 2015. p. 426-453.

3. Laudicina RJ. Hemoglobinopathies: qualitative defects. In: Clinical laboratory hematology. 3rd ed. New Jersey: Pearson; 2015. p.231–50.

4. Harmening DM, Yang D, Zeringer H. Hemolytic anemias: extracorpuscular defects. 5th ed. Philadelphia: F.A. Davis Company; 2009. p. 250-79).

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A Laboratory Guide to Clinical Hematology by Michelle To and Valentin Villatoro is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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