|  | Conditions & Treatments | Hemorrhage

Low Hemoglobin (Anemia): Causes, Symptoms & Diagnostic Approach

Anemia (hemoglobin <13 g/dL men, <12 g/dL women per WHO) reflects reduced oxygen-carrying capacity. Causes are categorized by mechanism or RBC indices (MCV).

Causes by Mechanism

1. Decreased Production

  • Nutritional: Iron deficiency (most common globally), B12 deficiency, folate deficiency, vitamin A, copper.
  • Chronic disease (ACD/AI): Inflammation → hepcidin ↑ → iron sequestration; EPO blunted; erythropoiesis suppressed. (RA, CKD, cancer, IBD, chronic infections).
  • Renal disease: EPO deficiency (primary cause in CKD).
  • Endocrine: Hypothyroidism, hypogonadism, adrenal insufficiency.
  • Bone marrow failure: Aplastic anemia, MDS, leukemia, myelofibrosis, infiltration (metastases, lymphoma).
  • Drugs: Chemo, TKIs, ARVs, linezolid, ganciclovir, valproate.

2. Increased Destruction (Hemolysis)

  • Intrinsic (intracorpuscular): Hereditary spherocytosis, G6PD deficiency, pyruvate kinase deficiency, sickle cell, thalassemia, PNH.
  • Extrinsic (extracorpuscular): Autoimmune (warm/cold AIHA), TTP/HUS, DIC, malaria, babesiosis, drugs (cephalosporins, methyldopa), mechanical (prosthetic valves, HUS).
  • Labs: ↑ LDH, ↑ indirect bilirubin, ↓ haptoglobin, ↑ reticulocytes, spherocytes/schistocytes on smear.

3. Blood Loss

  • Acute: Trauma, surgery, postpartum, GI bleed (varices, ulcer), ectopic pregnancy.
  • Chronic: Menorrhagia, GI (angiodysplasia, IBD, neoplasia), NSAID gastropathy, hookworm, urinary loss.
  • Leads to iron deficiency → microcytic anemia.

Classification by MCV (Mean Corpuscular Volume)

MCVCategoryKey Causes
<80 fLMicrocyticIron deficiency, thalassemia, ACD (late), sideroblastic, lead
80-100 fLNormocyticACD (early), CKD, hemolysis, acute blood loss, marrow failure, endocrine
>100 fLMacrocyticB12/folate deficiency, alcohol, liver disease, hypothyroid, drugs (hydroxyurea, metformin), MDS

Key Symptoms

  • Fatigue, exertional dyspnea, tachycardia, pallor, headache, dizziness, cold intolerance.
  • Specific: pica (ice = pagophagia → iron deficiency), jaundice (hemolysis), neuropathy (B12), glossitis (B12/folate/iron), koilonychia (iron).

Essential Initial Workup

  1. CBC with indices (MCV, RDW), reticulocyte count, peripheral smear.
  2. Iron studies: ferritin (acute phase reactant — interpret with CRP), serum iron, TIBC, transferrin saturation.
  3. B12, folate (RBC folate better).
  4. LDH, haptoglobin, indirect bilirubin (if hemolysis suspected).
  5. Reticulocyte production index (RPI) — assesses marrow response.
  6. Occult blood (stool), urinalysis.

Special Considerations

  • Menstruating women: Most common cause = iron deficiency from menstrual loss.
  • Pregnancy: Physiologic anemia (dilution); true anemia = Hb <11 (1st/3rd tri), <10.5 (2nd tri).
  • Elderly: "Unexplained anemia" (UA) in 30% — often multifactorial (CKD, inflammation, nutrient, MDS).

Anemia is a sign, not a diagnosis. Identify the underlying mechanism for targeted treatment. Iron deficiency without obvious cause in adult male/postmenopausal female → GI evaluation mandatory.

Hemorrhage - Related Articles