What are the common and uncommon causes of hemolysis and lymphopenia?

Common and Uncommon Causes of Hemolysis and Lymphopenia

The most common causes of hemolysis are autoimmune hemolytic anemia, microangiopathy, and infections, while lymphopenia most frequently results from excess catabolism (HIV, chemotherapy, immunosuppressive therapy, corticosteroids) and abnormal lymphocyte trapping (viral infections, septic shock, splenomegaly). 1, 2

Hemolysis: Common Causes

Acquired Hemolysis (Most Frequent)

Immune-Mediated Hemolytic Anemia is the leading cause and requires DAT (direct antiglobulin test) for diagnosis 1, 3:

• Autoimmune hemolytic anemia (AIHA): DAT positive with IgG and/or C3d, presenting with reticulocytosis, increased unconjugated bilirubin, elevated LDH, and decreased haptoglobin 3, 4

  • Warm-antibody AIHA (wAIHA): IgG antibodies against band 3 protein, treated with glucocorticoids and steroid-sparing agents 4
  • Cold agglutinin disease (CAD): Monoclonal IgM antibodies, DAT positive only for C3d, requires keeping patient warm 4

• Drug-induced immune hemolytic anemia: Appears as wAIHA with DAT IgG and/or C3d, may resolve after stopping the offending drug 4

• Immune checkpoint inhibitor-induced hemolysis: Median onset 40 days after ICPi therapy, managed by holding ICPi, corticosteroids, and IVIG 5

Microangiopathic Hemolytic Anemia (MAHA): Red cell membrane damage in circulation produces schistocytes on peripheral smear, seen in disseminated intravascular coagulation, TTP, and prosthetic cardiac valves 1, 6

Infectious Causes: Malaria and babesiosis directly invade red blood cells 1

Hereditary Hemolysis (Less Common)

• Glucose-6-phosphate dehydrogenase (G6PD) deficiency: Hemolysis triggered by oxidative stress 1
• Hereditary spherocytosis: Spherocytes on smear, positive family history, negative DAT 1
• Hemoglobinopathies: Sickle cell anemia and thalassemia cause chronic hemolysis 1

Hemolysis: Uncommon Causes

• Paroxysmal nocturnal hemoglobinuria (PNH): DAT negative, requires flow cytometry for diagnosis 6
• Acquired hemophilia A: Factor VIII inhibitor causing subcutaneous, GI, genitourinary, and retroperitoneal bleeding, associated with ICPi therapy 5
• Metal intoxications: Target red blood cells or capillary endothelium 6
• Passenger lymphocyte syndrome: Post-transplantation when donor B-cell antibodies react with recipient RBCs 4

Lymphopenia: Common Causes

Lymphopenia is defined as <1500/mm³ in adults and <4500/mm³ in children under 8 months 2

Excess Catabolism (Most Frequent)

• HIV infection: Leading infectious cause of lymphopenia 2
• Chemotherapy and immunosuppressive therapy: Direct lymphocyte destruction 2
• Systemic lupus erythematosus: Can cause both lymphopenia and hemolysis (MAS-associated HLH) 2, 7
• Radiotherapy: Destroys lymphocytes 2

Abnormal Lymphocyte Trapping

• Viral infections: Lymphocytes sequestered in tissues 2
• Septic shock and extended burns: Abnormal distribution 2
• Splenomegaly: Physical trapping of lymphocytes 2
• Corticosteroids: Cause lymphocyte redistribution 2
• Systemic granulomatosis: Lymphocyte sequestration 2

Production Defects

• Malnutrition and zinc deprivation: Impaired lymphocyte production 2
• Primary immune deficiencies: Congenital disorders 2

Lymphopenia: Uncommon Causes

• Haemophagocytic lymphohistiocytosis (HLH): Uncontrolled activation of cytotoxic T lymphocytes and macrophages causing cytokine storm, presenting with prolonged fever, cytopenias, hepatosplenomegaly, hypofibrinogenemia, hypertriglyceridemia, and markedly elevated ferritin (>500 μg/L) 7

  • MAS-associated HLH in SLE: Responds to corticosteroids 7
  • Malignancy-associated HLH (e.g., acute leukemia): Poor prognosis despite aggressive treatment 7

• Chronic lymphocytic leukemia (CLL): Can present with lymphopenia before leukemic manifestation, may be associated with autoimmune hemolytic anemia 8, 9

• Immune checkpoint inhibitor therapy: Presents with fever, cough, runny nose, enlarged lymph nodes, painful joints, skin rash, and night sweats 5

• Idiopathic CD4 lymphocytopenia: Mechanism poorly understood 2

• Ethnic variation: Ethiopians have naturally lower lymphocyte counts 2

• Renal insufficiency and lymphoma: Mechanisms remain unclear 2

Critical Diagnostic Pitfalls

When both hemolysis and lymphopenia coexist, immediately consider haemophagocytic lymphohistiocytosis (HLH), which requires urgent multidisciplinary management as it carries high mortality without early intervention 7. Look specifically for the constellation of prolonged fever, cytopenias affecting multiple cell lines, hepatosplenomegaly, hypofibrinogenemia, hypertriglyceridemia, and ferritin >500 μg/L.

For isolated hemolysis, the DAT result determines your diagnostic pathway: DAT-positive indicates immune causes requiring immunosuppression, while DAT-negative directs you toward hereditary disorders, PNH, or microangiopathic processes 3, 4.