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Anemia Workup (Clinical)

Name: Anemia Workup (Clinical)
Creator: Veli Bakalov, MD

Start with the MCV, finish by finding the source

Hematology/Oncology·Anemias & Red Cell Disorders·6 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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Work up anemia by MCV (microcytic <80, normocytic 80–100, macrocytic >100 fL), then the corrected reticulocyte count: high = blood loss or hemolysis, low = underproduction.
Iron deficiency: low ferritin (single best test), low iron, HIGH TIBC, low saturation; anemia of chronic disease: low iron, LOW TIBC, normal/high ferritin from hepcidin trapping iron.
New iron-deficiency anemia in a man or postmenopausal woman is GI malignancy until proven otherwise: colonoscopy (plus upper endoscopy); in premenopausal women think menses and pregnancy.
Oral ferrous sulfate every other day first (reticulocytes rise in ~1 week); IV iron for intolerance, malabsorption, ongoing losses, CKD, or IBD.
Thalassemia trait: very low MCV with normal/high RBC count, target cells, normal iron studies, Mentzer index <13; β-thalassemia trait has elevated HbA2; do not give iron.
B12 and folate deficiency both cause megaloblastic anemia with hypersegmented neutrophils and high homocysteine; only B12 raises methylmalonic acid and causes neurologic disease, so give B12 before folate.
Hemolysis: high LDH, indirect bilirubin, and reticulocytes with low haptoglobin; intravascular adds hemoglobinuria/hemosiderinuria, extravascular causes splenomegaly.
Coombs-positive: warm IgG (SLE, CLL, methyldopa, penicillins) → steroids; cold IgM (Mycoplasma, EBV). Coombs-negative: G6PD (bite cells, Heinz bodies), hereditary spherocytosis, sickle cell, schistocytes.
Restrictive transfusion: hemoglobin <7 g/dL in stable inpatients, <8 with active cardiac disease; each unit of packed RBCs raises Hb ~1 g/dL.

The framework: MCV first, then the reticulocyte count

Two numbers frame the workup. Classify every anemia by mean corpuscular volume (MCV): microcytic <80 fL, normocytic 80–100 fL, macrocytic >100 fL. Then check the reticulocyte count, corrected for the degree of anemia: a high count means the marrow is responding to blood loss or hemolysis; a low count means underproduction. A peripheral smear belongs in every workup.

Check the MCVMicro, normo, or macro sends you down three different roads.
Microcytic (<80)Iron deficiency, thalassemia, anemia of chronic disease: iron studies next.
Normocytic (80–100)Check reticulocytes: high = bleeding or hemolysis; low = chronic disease, CKD, marrow failure or infiltration.
Macrocytic (>100)Megaloblastic (B12/folate) vs non-megaloblastic causes.

MCV-based approach to anemia

Correcting the count. A raw percentage overstates output when the hematocrit is low, so multiply it by hematocrit ÷ 45; a reticulocyte production index below 2 signals inadequate production. Low-retic normocytic anemias include anemia of chronic disease, CKD (erythropoietin deficiency), early iron deficiency, and aplastic anemia or marrow infiltration.

Microcytic anemia: iron studies sort TAILS

TAILS. The microcytic differential is Thalassemia, Anemia of chronic disease, Iron deficiency, Lead poisoning, and Sideroblastic anemia. Iron deficiency is the most common cause overall; anemia of chronic disease is usually normocytic but can be microcytic. Iron studies separate them.

Ferritin is the single best test. Iron deficiency shows low ferritin, low serum iron, high TIBC (transferrin is upregulated), and low transferrin saturation, a picture of true depletion. Ferritin is an acute-phase reactant and rises with inflammation, so a normal ferritin in an inflamed patient does not fully exclude iron deficiency.

Anemia of chronic disease accompanies chronic infection, autoimmune disease, and malignancy. Inflammation (IL-6) raises hepcidin, which degrades ferroportin and blocks iron release from macrophages and absorption from the gut: a functional block, not true depletion. Expect low iron, low TIBC, low-normal saturation, and normal-to-high ferritin. Treat the underlying disease.

Iron studies across the microcytic anemias

Feature	Iron deficiency	Chronic disease	Thalassemia trait	Sideroblastic
Ferritin	Low	Normal–high	Normal	High
Serum iron	Low	Low	Normal	High
TIBC	High	Low	Normal	Normal–low
Saturation	Low	Low–normal	Normal	High
Clue	Low RBC count; Mentzer >13	Chronic inflammation; hepcidin	Normal/high RBC count, target cells; Mentzer <13	Ringed sideroblasts on Prussian blue marrow stain

Lead poisoning is an acquired cause of sideroblastic anemia; confirm it with a blood lead level.

Thalassemia trait. Suspect it when the MCV is very low but the RBC count is normal or high, target cells are present, and iron studies are normal. The Mentzer index (MCV ÷ RBC count) is <13 in thalassemia and >13 in iron deficiency. Electrophoresis shows elevated HbA2 in β-thalassemia trait; α-thalassemia trait has a normal adult electrophoresis and is a diagnosis of exclusion or genetic testing. Empiric iron does not help and risks overload.

Lead and other sideroblastic causes. Lead inhibits ferrochelatase and ALA dehydratase, causing basophilic stippling, abdominal pain, wrist or foot drop, and developmental delay in children; remove the exposure and chelate (succimer; EDTA plus dimercaprol when severe). Other causes of ringed sideroblasts include alcohol, isoniazid (vitamin B6 deficiency), copper deficiency, and X-linked ALAS2 mutations; pyridoxine treats many cases.

Iron deficiency: find the source, then replace

A symptom, not a diagnosis. In premenopausal women, menstrual loss and pregnancy are the usual explanations. In men and postmenopausal women, new iron-deficiency anemia is GI blood loss, and a GI malignancy, until proven otherwise: colonoscopy (and upper endoscopy) is mandatory to exclude colorectal cancer. Clues include pica, koilonychia, glossitis, and angular cheilitis; Plummer-Vinson syndrome adds an esophageal web. If endoscopy is unrevealing, test for celiac disease and H. pylori, which impair absorption.

Confirm deficiencyLow ferritin, high TIBC, low saturation.
Find the sourceMenses or pregnancy in premenopausal women; colonoscopy plus EGD in men and postmenopausal women.
Replace orallyFerrous sulfate, every-other-day dosing.
Check the responseReticulocytes rise in about a week; continue several months to refill stores.
Escalate if neededIV iron for intolerance, malabsorption, ongoing losses, CKD, or IBD.

Iron-deficiency anemia: stepwise management

Oral first, IV when it fails. Every-other-day dosing improves absorption and tolerability because each dose transiently raises hepcidin. Expect GI side effects (constipation, nausea, dark stools). A poor response suggests nonadherence, continued bleeding, or malabsorption.

Macrocytic anemia: B12 versus folate

Megaloblastic vs non-megaloblastic. Megaloblastic anemia reflects impaired DNA synthesis from B12 or folate deficiency (or drugs such as methotrexate and hydroxyurea); hypersegmented neutrophils are the tell. Non-megaloblastic macrocytosis lacks them: alcohol, liver disease, hypothyroidism, myelodysplastic syndrome, and brisk reticulocytosis.

Vitamin B12 vs folate deficiency

Feature	Vitamin B12	Folate
Classic causes	Pernicious anemia; strict vegan diet; gastrectomy; terminal ileal disease or resection; metformin	Poor diet (alcohol use disorder), pregnancy, chronic hemolysis, methotrexate, phenytoin
Body stores	Years	Months
Neurologic disease	Subacute combined degeneration, neuropathy	Spared
Methylmalonic acid	Elevated	Normal
Homocysteine	Elevated	Elevated

Both produce megaloblastic changes with hypersegmented neutrophils; methylmalonic acid is the discriminator.

Pernicious anemia is the classic cause of B12 deficiency: autoimmune destruction of parietal cells removes intrinsic factor. Anti–intrinsic factor antibodies are highly specific, and the atrophic gastritis raises gastric cancer risk. Neurologic deficits can appear before (or without) anemia.

Always give B12 before folate: folate alone corrects the blood count but can let the neurologic damage worsen.

Hemolysis: confirm it, then sort it

The hemolysis panel. Hemolysis raises LDH, indirect (unconjugated) bilirubin, and the reticulocyte count while dropping haptoglobin, which is consumed as it binds free hemoglobin. The direct antiglobulin (Coombs) test then detects antibody-mediated immune hemolysis, and the smear identifies the mechanism.

Intravascular vs extravascular hemolysis

Feature	Intravascular	Extravascular
Site	Within the circulation	Splenic and hepatic macrophages
Distinctive findings	Very low haptoglobin, hemoglobinuria, hemosiderinuria	Splenomegaly, jaundice, spherocytes
Examples	PNH, microangiopathic hemolytic anemia, transfusion reaction	Warm AIHA, hereditary spherocytosis

Warm AIHA (IgG, Coombs positive): SLE, CLL, methyldopa, penicillins. Corticosteroids first; rituximab or splenectomy only for refractory disease.
Cold agglutinin disease (IgM): Mycoplasma pneumoniae, EBV mononucleosis; acral cyanosis with cold exposure. Avoid cold; steroids work poorly.
Coombs negative: G6PD deficiency (bite cells, Heinz bodies after oxidant stress such as sulfa drugs, primaquine, or fava beans), hereditary spherocytosis, sickle cell disease, and microangiopathy with schistocytes (TTP, HUS, DIC, mechanical valves).

Spherocytes appear in both hereditary spherocytosis and warm AIHA; the DAT separates them. G6PD activity can read falsely normal during an acute episode, so repeat it after recovery.

Transfusion and treatment principles

<7 g/dLrestrictive threshold for most stable inpatients

<8 g/dLthreshold with active cardiac disease or symptoms

~1 g/dLhemoglobin rise per unit of packed red cells

Treat the cause, not the number. Active hemorrhage and instability are transfused on clinical grounds. Chronic anemia is corrected by treating its cause (iron, B12, or folate; control of inflammation; erythropoiesis-stimulating agents in CKD once iron is replete) rather than by reflexive transfusion.