Hemolytic Anemia

Last Updated: January 13, 2019
Keywords: USMLE Step 1, Hemolytic Anemia, Warm Autoimmune Hemolytic Anemia, WAIHA

-shortness of breath, fatigue, dark urine (anemia secondary to RBC destruction)
-history of SLE, CLL, drugs such as alpha-methyldopa (old anti-HTN drug)

Investigations
-low HCT, low RBC count, elevated indirect bilirubin
-Direct Coombs Test (DAT): positive (AHG/Coomb’s reagent binds to antibodies on patient’s RBCs causing agglutination)) for warm agglutins (at temperatures > 37C)

Extrinsic Hemolytic Anemia
Autoimmune Hemolytic Anemia
-most are idiopathic
Warm Autoimmune Hemolytic Anemia (WAIHA)
-presentation as above
-IgG autoantibody-mediated
-DAT positive at temperatures >37C

Cold Autoimmune Hemolytic Anemia (CAIHA)
– blue fingers/toes at cold temperatures
-history of CLL, mycoplasma pneumoniae, and infectious mononucleosis
-IgM autoantibody and complement-mediated
-DAT positive at temperatures < 30C

Fig: Direct and Indirect Antiglobulin (Coomb’s) test (First Aid, 2018)
—
Microangiopathic Hemolytic Anemia (MiAHA)
-history of DIC, TTP/HUS, SLE, HELLP syndrome, or hypertensive emergency (RBCs damaged when passing through a very narrowed opening)
-peripheral smear shows schistocytes (helmet cells)

Macroangiopathic Hemolytic Anemia (MaAHA)
-history of prosthetic heart valve or AS (not so small narrowed opening)
-peripheral smear as in MiAHA

Infection
-malaria, babasia causing increased destruction of RBCs

Case:

A 27-year-old woman with a past medical history significant for type 1 diabetes mellitus, systemic lupus erythematosus, and depression presents with shortness of breath, fatigue, and dark urine for the past week. Laboratory studies reveal the following:

Hematocrit: 28%
Hemoglobin: 10 g/dL
RBC count: 2.8 million/mm³
WBC count: 7500/mm³
Hemoglobin A_1c: 5%
Indirect bilirubin: 2.8 mg/dL
Direct bilirubin: 0.2 mg/dL

Which test result confirms the diagnosis in this patient?