Microcytic anemia: Pathology review


00:00 / 00:00



Microcytic anemia: Pathology review

Hematological system


Iron deficiency anemia



Sideroblastic anemia

Anemia of chronic disease

Lead poisoning

Hemolytic disease of the newborn

Glucose-6-phosphate dehydrogenase (G6PD) deficiency

Autoimmune hemolytic anemia

Pyruvate kinase deficiency

Paroxysmal nocturnal hemoglobinuria

Sickle cell disease (NORD)

Hereditary spherocytosis

Anemia of chronic disease

Aplastic anemia

Fanconi anemia

Megaloblastic anemia

Folate (Vitamin B9) deficiency

Vitamin B12 deficiency

Fanconi anemia

Diamond-Blackfan anemia

Heme synthesis disorders

Acute intermittent porphyria

Porphyria cutanea tarda

Lead poisoning

Coagulation disorders


Vitamin K deficiency

Platelet disorders

Bernard-Soulier syndrome

Glanzmann's thrombasthenia

Hemolytic-uremic syndrome

Immune thrombocytopenic purpura

Thrombotic thrombocytopenic purpura

Mixed platelet and coagulation disorders

Von Willebrand disease

Disseminated intravascular coagulation

Heparin-induced thrombocytopenia

Thrombosis syndromes (hypercoagulability)

Antithrombin III deficiency

Factor V Leiden

Protein C deficiency

Protein S deficiency

Antiphospholipid syndrome


Hodgkin lymphoma

Non-Hodgkin lymphoma


Chronic leukemia

Acute leukemia

Leukemoid reaction

Leukemoid reaction

Dysplastic and proliferative disorders

Myelodysplastic syndromes

Polycythemia vera (NORD)

Myelofibrosis (NORD)

Essential thrombocythemia (NORD)

Langerhans cell histiocytosis

Mastocytosis (NORD)

Plasma cell dyscrasias

Multiple myeloma

Monoclonal gammopathy of undetermined significance

Waldenstrom macroglobulinemia

Hematological system pathology review

Microcytic anemia: Pathology review

Non-hemolytic normocytic anemia: Pathology review

Intrinsic hemolytic normocytic anemia: Pathology review

Extrinsic hemolytic normocytic anemia: Pathology review

Macrocytic anemia: Pathology review

Heme synthesis disorders: Pathology review

Coagulation disorders: Pathology review

Platelet disorders: Pathology review

Mixed platelet and coagulation disorders: Pathology review

Thrombosis syndromes (hypercoagulability): Pathology review

Lymphomas: Pathology review

Leukemias: Pathology review

Plasma cell disorders: Pathology review

Myeloproliferative disorders: Pathology review


Microcytic anemia: Pathology review

USMLE® Step 1 questions

0 / 8 complete


USMLE® Step 1 style questions USMLE

of complete

A 2-year-old boy is brought to the clinician by his parents due to easy fatigability and growth delay. They recently immigrated to the United States. The mother did not receive any prenatal care in her home country. The child was born at term by a normal vaginal delivery. He is at the 30th percentile for length and below the 10th percentile for weight. Temperature is 37.2°C (98.9°F), pulse is 115/min, respirations are 25/min, and blood pressure is 85/60 mmHg. Abdominal examination shows hepatosplenomegaly. Hematological tests and hemoglobin electrophoresis are obtained:  
 Laboratory value  Result 
 Hemoglobin (Hb)  10.8 g/dL 
 Hematocrit (Hct 32% 
 Erythrocyte count  5.7 million/mm3 
 Hemoglobin A(HbA2)   6.5% 
 Fetal hemoglobin (HbF)  60% 
 Hemoglobin A (HbA1 None 
 Hemoglobin S (HbS None 

Which of the following is the most likely diagnosis? 

Memory Anchors and Partner Content


Content Reviewers

Yifan Xiao, MD

Antonia Syrnioti, MD


Maria Emfietzoglou, MD

Sam Gillespie, BSc

Salma Ladhani, MD

Ursula Florjanczyk, MScBMC

At the family medicine center, there is a 60-year-old Indigenous American named Istu who came to visit the doctor because of his progressive fatigue and difficulty in swallowing. Next to him, there is a mother from Greece with her child, Thalia, who is 10 months old. Little Thalia appeared healthy at birth but in the past 2 months, her mother noticed that her face was often pale, she’s been less active, and there was a mass in her belly.

Both Istu and Thalia are suffering from anemia, which is defined as lower than average levels of hemoglobin, typically below 13.5 g/dL in adult men and below 12.0 g/dL in adult women. For children, this level varies based on the age. Now, anemias can be broadly grouped into 3 categories based on mean corpuscular volume, or MCV, which reflects the volume of a Red blood cell or RBC. So microcytic anemia is where the MCV is lower than 80 fL, normocytic, with an MCV between 80 and 100 fL, and macrocytic, with an MCV larger than 100 fL. Now, let’s focus on the microcytic anemias, and the most common causes are iron deficiency anemia, lead poisoning, sideroblastic anemia, and thalassemias. Although microcytic anemia can also present in anemia of chronic disease, which is caused by Inflammatory conditions like rheumatoid arthritis, and systemic lupus erythematosus or SLE, it’s usually classified as normocytic anemia.

Now iron deficiency anemia, lead poisoning, and sideroblastic anemia are caused by defective heme synthesis, while thalassemias are caused by defective globin chains. Normally, RBCs are loaded with millions of copies of a protein called hemoglobin. Hemoglobin is actually made up of four peptide, or globin, chains, each bound to a heme group. Those 4 heme molecules have, right in the middle, iron, which binds to oxygen and allows it to move in our body.

Okay, so let’s look at iron deficiency anemia which could be caused by decreased intake, decreased absorption, increased demand, or increased loss of iron. For your exams, it’s important to know that the clues to help you identify this disorder are often based on the patient’s history. A high yield fact is that the most common cause of iron deficiency is chronic blood loss. This includes women with heavy menstruation or people with bleeding gastric ulcers, and, most importantly, elderly males with colon cancer that can bleed.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Goldman-Cecil Medicine" Saunders (2015)
  4. "Letter to the Editor: Correcting iron deficiency" Australian Prescriber (2017)
  5. "Alpha-thalassemia" Genetics in Medicine (2011)
  6. "Iron deficiency anaemia" Lancet (2016)
  7. "Lead screening and prevalence of blood lead levels in children aged 1-2 years--Child Blood Lead Surveillance System, United States, 2002-2010 and National Health and Nutrition Examination Survey, United States, 1999-2010" MMWR Suppl. (2014)
  8. "Sideroblastic anemia: diagnosis and management" Hematol Oncol Clin North Am. (2014)

Copyright © 2023 Elsevier, except certain content provided by third parties

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.