Hemolytic Anemia Management: AIHA, G6PD, Spherocytosis & PNH
The DAT and the smear pick the culprit—and the therapy
Confirming and classifying hemolysis
Markers of hemolysis. Red cell destruction raises LDH and indirect bilirubin, lowers haptoglobin, and provokes reticulocytosis. Haptoglobin binds free hemoglobin and is cleared with it, so an undetectable haptoglobin plus a high LDH strongly favors hemolysis. Intravascular lysis adds hemoglobinemia, hemoglobinuria (dipstick positive for heme without RBCs on microscopy), and, days later, hemosiderinuria.
- Direct antiglobulin test (DAT)Positive = immune hemolysis: IgG ± C3 suggests warm AIHA; C3 alone suggests cold agglutinin disease
- DAT negative → read the smearSpherocytes (hereditary spherocytosis), bite cells and blister cells (G6PD deficiency), schistocytes (TTP, HUS, DIC, mechanical valves)
- Smear unrevealing with hemoglobinuriaPeripheral blood flow cytometry for CD55/CD59-deficient cells (PNH)
Immune hemolysis: warm, cold, and drug-induced
Warm AIHA. IgG autoantibodies (± C3) bind red cells at body temperature; splenic macrophages nibble the coated membrane, leaving microspherocytes, and the DAT is positive. About half of cases are idiopathic; secondary causes include SLE, CLL (the most common secondary cause) and other lymphomas, and drugs (methyldopa, penicillins, cephalosporins).
Treating warm AIHA. Prednisone about 1 mg/kg/day is first line; most patients respond within about 3 weeks, followed by a slow taper. Rituximab is used for relapse or steroid dependence, or up front in severe disease, and splenectomy is reserved for refractory cases. Give folic acid and stop any culprit drug.
Never withhold transfusion from a patient with life-threatening AIHA because the crossmatch is incompatible—give the least-incompatible units slowly.
Cold agglutinin disease. IgM autoantibodies bind red cells in the cool peripheral circulation and fix complement; by the time cells rewarm the IgM has dissociated, leaving C3 on the surface. The DAT is therefore positive for C3 only, the smear shows agglutination, and patients develop acrocyanosis and livedo in the cold. C3-coated cells are cleared mainly by the liver, with some intravascular lysis. Primary disease reflects a clonal B-cell disorder; secondary causes include Mycoplasma pneumoniae (anti-I), EBV (anti-i), and lymphoma or Waldenström macroglobulinemia. Agglutinated cells make automated analyzers report a falsely high MCV and MCHC with a low RBC count; rewarming the sample to 37°C corrects the indices.
Treating cold agglutinin disease. Keep the patient warm and give IV fluids and blood through an in-line warmer. Rituximab (± bendamustine) targets the B-cell clone, sutimlimab (anti-C1s) blocks the classical complement pathway, and plasma exchange can bridge a severe crisis. Glucocorticoids and splenectomy are generally ineffective.
| Feature | Warm AIHA | Cold agglutinin disease |
|---|---|---|
| Antibody | IgG, active at 37°C | IgM, active below 37°C |
| DAT | IgG ± C3 | C3 only |
| Smear | Spherocytes | Agglutination |
| Site of clearance | Spleen (extravascular) | Liver, plus some intravascular lysis |
| Associations | Idiopathic, SLE, CLL, drugs | Clonal B-cell disease, Mycoplasma, EBV, lymphoma |
| Treatment | Steroids → rituximab → splenectomy | Warmth, rituximab, sutimlimab; steroids and splenectomy fail |
Drug-induced immune hemolysis. High-dose IV penicillin binds the red cell membrane as a hapten; ceftriaxone and cefotetan form immune complexes that cause abrupt, severe intravascular hemolysis; methyldopa induces true warm autoantibodies, and its positive DAT can persist for months after the drug is stopped even as hemolysis subsides. The DAT is positive, and stopping the drug is the key treatment.
G6PD deficiency
Mechanism. X-linked G6PD deficiency, common in people of African, Mediterranean, and Asian ancestry, limits NADPH production, so red cells cannot keep glutathione reduced. Oxidant stress denatures hemoglobin into Heinz bodies (seen with supravital stains), which splenic macrophages pluck out to leave bite cells. Episodic hemolysis begins 1–3 days after the trigger.
Triggers. Infection (the most common), fava beans, and oxidant drugs—dapsone, primaquine and tafenoquine, rasburicase, sulfonamides, and nitrofurantoin. Rasburicase generates hydrogen peroxide and can cause severe hemolysis and methemoglobinemia, so G6PD status must be checked before rasburicase, primaquine or tafenoquine, and dapsone.
During or shortly after an episode (or after transfusion), G6PD activity can read falsely normal because the oldest, most deficient cells have been destroyed and reticulocytes carry more enzyme. Repeat the assay about 3 months later.
Management. Stop the trigger, treat infection, hydrate, and transfuse for severe anemia.
Hereditary spherocytosis
Pathophysiology and diagnosis. Usually autosomal dominant, HS results from defects in ankyrin, spectrin, or band 3 that destabilize the membrane; cells lose surface area, become spherocytes, and are trapped in the spleen. Look for a family history, anemia, jaundice, splenomegaly, reticulocytosis, an elevated MCHC, and DAT-negative spherocytes. Reduced eosin-5-maleimide (EMA) binding on flow cytometry confirms the diagnosis; increased osmotic fragility is the older test.
Complications. Calcium bilirubinate (pigment) gallstones, even in children; aplastic crisis when parvovirus B19 halts erythropoiesis (a sudden hemoglobin drop with reticulocytopenia); hemolytic crises with infections; and megaloblastic crisis from folate deficiency.
A falling hemoglobin with a LOW reticulocyte count in any chronic hemolytic anemia is parvovirus B19 aplastic crisis until proven otherwise—transfuse and support until the marrow recovers.
Management. Folic acid for everyone and transfusion for crises. Splenectomy for severe (or symptomatic moderate) disease, ideally after about age 6, stops hemolysis although spherocytes persist. Vaccinate against pneumococcus, meningococcus, and Haemophilus influenzae type b at least 2 weeks before surgery, and remove the gallbladder at the same time if stones are present.
Paroxysmal nocturnal hemoglobinuria
Mechanism. An acquired PIGA mutation in a hematopoietic stem cell prevents synthesis of the GPI anchor, so the clone's cells lack CD55 (decay-accelerating factor) and CD59 (membrane inhibitor of reactive lysis). Unchecked complement assembles the membrane attack complex, causing intravascular hemolysis.
Presentation. Dark urine (often in the morning), fatigue, and symptoms of nitric oxide scavenging by free hemoglobin—dysphagia, abdominal pain, erectile dysfunction. Cytopenias reflect overlap with aplastic anemia, and chronic urinary iron loss causes iron deficiency. Venous thrombosis at unusual sites—hepatic veins (Budd–Chiari), portal, mesenteric, and cerebral veins—is the leading cause of death.
Diagnosis. DAT-negative intravascular hemolysis with a very high LDH, especially with cytopenias or unusual clots, calls for peripheral blood flow cytometry showing loss of CD55/CD59 on red cells and of FLAER binding on granulocytes and monocytes. Marrow biopsy assesses overlapping aplastic anemia but does not diagnose PNH.
| Feature | Hereditary spherocytosis | G6PD deficiency | PNH |
|---|---|---|---|
| Defect | Inherited membrane protein | Inherited enzyme (X-linked) | Acquired PIGA mutation |
| Hemolysis | Chronic, extravascular | Episodic, after oxidant stress | Chronic, intravascular, with flares |
| Smear clue | Spherocytes, ↑MCHC | Bite cells, Heinz bodies | Nonspecific |
| Key test | EMA binding | G6PD activity (~3 months after an episode) | Flow cytometry for CD55/CD59, FLAER |
| Treatment | Folate; splenectomy if severe | Avoid triggers | C5 inhibitor; anticoagulate clots |
Treatment. The C5 inhibitors eculizumab (every 2 weeks) and ravulizumab (every 8 weeks) halt intravascular hemolysis and reduce thrombosis. Because the membrane attack complex is essential for killing Neisseria, vaccinate with MenACWY and MenB at least 2 weeks before starting (or give antibiotic cover). Anticoagulate thrombosis, and support with folate, iron, and transfusion as needed. Allogeneic HSCT is the only cure and is reserved for marrow failure or refractory disease.
On C5 inhibitors, C3 still coats PNH cells, so some extravascular hemolysis persists and the DAT may turn C3-positive; proximal complement inhibitors such as pegcetacoplan (C3) and iptacopan (factor B) address this.