Microcytic Anemia and Hemoglobinopathies

Comprehensive review flashcards covering microcytic hypochromic anemias, iron metabolism, iron deficiency anemia, sideroblastic anemia, and alpha/beta thalassemia syndromes.

What morphological feature of a normal erythrocyte is represented by this diagram showing a $1/3$ central division?

The normal central pallor, which occupies approximately $1/3$ of the diameter of a normal red blood cell.

To what cellular structure should the size of a red blood cell be compared when reviewing a peripheral blood smear?

The nucleus of a normal small lymphocyte.

What conditions are represented by the mnemonic acronym TAILS in the differential diagnosis of microcytic hypochromic anemia?

Thalassemia, Anemia of Chronic Inflammation (disease), Iron deficiency anemia, Lead poisoning, and Sideroblastic anemia.

What peripheral blood smear artifact is shown in this field, and what two conditions commonly cause it?

Punched out water artifact, caused by slow drying when preparing a smear in a humid room or in specimens from severely anemic patients.

How many amino acids comprise a normal $\alpha$-globin chain and a normal $\beta$-globin chain?

The $\alpha$ chain contains $141$ amino acids and the $\beta$ chain contains $146$ amino acids.

What are the three molecular components that make up a complete hemoglobin molecule?

$4$ globin chains (amino acids), $4$ iron molecules ($Fe^{2+}$), and $4$ protoporphyrin molecules.

What are the four general pathophysiological categories of hypochromic microcytic anemias?

1. Disorders of iron metabolism (e.g., IDA, ACI); 2. Disorders of heme synthesis (e.g., Sideroblastic Anemia); 3. Disorders of globin synthesis (e.g., Thalassemia syndromes); 4. Disorders of porphyrin synthesis (e.g., Lead poisoning).

How are the red cell indices MCH and MCHC calculated from automated CBC parameters?

$\text{MCH} = \frac{\text{Hgb}}{\text{RBC}}$ and $\text{MCHC} = \frac{\text{Hgb}}{\text{Hct}}$.

How does hepcidin regulate systemic iron absorption and release?

Hepcidin acts as the gatekeeper of iron: increased iron causes increased hepcidin, which decreases iron absorption; decreased iron causes decreased hepcidin, which increases iron absorption.

During erythrophagocytosis, what are the metabolic breakdown fates of the globin chains and the porphyrin ring?

Globin chains return to the amino acid pool; the heme group's porphyrin ring converts to biliverdin, which is then converted into bilirubin.

What percentage of iron is normally recycled in healthy adults compared to infants?

Adults normally recycle approximately $95\%$ of their iron, whereas infants recycle only $70\%$ and require more dietary or supplemented iron.

What are the daily iron intake requirements for males/infants, premenopausal women, and children?

Males/Infants: $1\,\text{mg/day}$; Premenopausal women: $0.2-2.0\,\text{mg/day}$; Children: $0.5\,\text{mg/day}$.

Which beverage acts as an iron absorption enhancer, and what common dietary items act as iron inhibitors?

Orange juice enhances absorption by reducing ferric iron ($Fe^{3+}$) to absorbable ferrous iron ($Fe^{2+}$); tannins (found in tea and red wine) and nuts, seeds, and grains act as inhibitors.

What are the two most common causes of prolonged blood loss leading to iron deficiency anemia?

Gastrointestinal (GI) bleeds and excessive menstrual bleeding.

At which anatomical sites in the gastrointestinal tract does iron absorption primarily take place?

The duodenum and proximal jejunum.

Why are infants over $6$ months of age fed breast milk or cow's milk more susceptible to IDA than formula-fed infants?

Breastfed infants are $11\times$ more likely to develop IDA after $6$ months due to high growth demand without fortification, cow's milk is low in iron, whereas commercial infant formula is fortified with iron.

What characterizes defective iron utilization in conditions like sideroblastic anemia and anemia of chronic inflammation?

Iron is trapped inside storage macrophages and cannot move into the serum or bone marrow, leading to elevated ferritin but decreased serum iron available for erythropoiesis.

What clinical sign of severe iron deficiency anemia is demonstrated on the fingernails in this photograph?

Spooning of the nail beds (koilonychia).

What physical examination finding of severe anemia is shown on inspection of the eye in this image?

Conjunctival pallor.

What oral mucosal symptom of severe iron deficiency anemia is displayed in this patient?

Chapped lips noted at the corners of the mouth (angular cheilitis).

What is PICA, and which non-food substances are most commonly craved in severe iron deficiency anemia?

PICA is a craving for unusual non-food substances, commonly including dirt, clay, or ice.

What does Total Iron Binding Capacity (TIBC) measure, and how does it correlate with available transferrin capacity?

TIBC measures how much transferrin is available to carry iron; an increase in available binding capacity corresponds to an increased TIBC.

At what percentage of transferrin saturation is erythropoiesis classified as ineffective?

A transferrin saturation of $<16\%$.

What are the normal reference ranges for serum iron, TIBC, and transferrin saturation?

Serum iron: $9-30\,\mu\text{mol/L}$ (female), $12-31\,\mu\text{mol/L}$ (male); TIBC: $45-81\,\mu\text{mol/L}$; Transferrin saturation: $20\%-50\%$.

What hemoglobin concentrations define an 'ALERT' level versus a 'CRITICAL' level in iron deficiency management?

ALERT is a hemoglobin concentration of $<80\,\text{g/L}$; CRITICAL is a hemoglobin concentration of $<60\,\text{g/L}$.

What are the three progressive stages of developing iron deficiency, and which iron study parameter decreases first?

The stages are: 1. Iron depletion; 2. Iron deficient erythropoiesis; 3. Iron deficiency anemia. Ferritin decreases first during iron depletion while serum iron remains normal.

During oral or intravenous iron therapy, how does iron distribute before ferritin storage pools rebuild?

Administered iron goes directly into the serum to be utilized by the bone marrow for hemoglobin synthesis; ferritin stores only begin to rebuild once hemoglobin normalizes.

Approximately how much does the transfusion of $1$ unit of blood increase a patient's hemoglobin concentration?

Approximately $10\,\text{g/L}$.

Why is the platelet count commonly elevated in patients with iron deficiency anemia?

Reactive thrombocytosis occurs as a marrow compensation reaction to bleeding, and the marrow may shift to producing other cell lines when erythropoiesis slows.

What are the characteristic bone marrow findings in severe iron deficiency anemia when stained with Perls' Prussian blue?

Decreased to absent stainable iron, erythroid hyperplasia stimulated by elevated EPO, and a decreased M:E ratio of $1:1$ (normal is $2:1$ to $5:1$).

What formula defines the Mentzer Index, and what cutoff values differentiate Thalassemia from Iron Deficiency Anemia?

$\text{Mentzer Index} = \frac{\text{MCV (fL)}}{\text{RBC (}\times 10^{12}\text{/L)}}$. A value $<13$ indicates Thalassemia is more likely, whereas a value $>13$ suspects Iron Deficiency.

What abnormal erythroid precursor is shown in this bone marrow aspirate stained with Prussian blue?

A ringed sideroblast, diagnostic of sideroblastic anemia.

What is the underlying pathophysiological defect in sideroblastic anemia?

A defect in mitochondrial heme synthesis where iron is present and available but cannot be properly incorporated into protoporphyrin, trapping iron within the mitochondria.

What are the most common congenital and acquired causes of sideroblastic anemia?

Congenital: X-linked recessive (most common); Acquired: Alcoholism (most common), or myelodysplastic syndrome (MDS - Refractory Anemia with Ringed Sideroblasts [RARS]).

What erythrocyte inclusion bodies containing iron aggregates are visible in this peripheral blood film?

Pappenheimer bodies (siderotic granules).

How do qualitative hemoglobinopathies differ from quantitative hemoglobinopathies?

Qualitative hemoglobinopathies involve structural gene substitutions yielding abnormal globin chains (e.g., HbS, HbC; typically normocytic normochromic), whereas quantitative hemoglobinopathies involve gene deletions/additions yielding reduced globin chain synthesis (thalassemias; typically hypochromic microcytic).

What are the normal proportions of adult hemoglobins HbA, $\text{HbA}_2$, and HbF in a healthy individual?

$\text{HbA} (\alpha_2\beta_2) > 95\%$, $\text{HbA}_2 (\alpha_2\delta_2) < 3.5\%$, and $\text{HbF} (\alpha_2\gamma_2) < 2\%$.

By what age does infant $\beta$-chain globin production reach adult percentages, and when does HbF decline to less than $2\%$?

$\beta$-chain production reaches adult percentages between $3$ and $6$ months, and HbF falls below $2\%$ by $2$ years of age.

Which chromosomes carry the genes encoding the $\alpha$-globin and $\beta$-globin chains, respectively?

$\alpha$-globin genes are located on chromosome $16$ ($4$ total genes, $2$ from each parent); $\beta$-globin genes are located on chromosome $11$ ($2$ total genes, $1$ from each parent).

What are the classic CBC and hemoglobin electrophoresis findings in Beta Thalassemia Minor (trait)?

Erythrocytosis (elevated RBC count) with normal RDW, microcytic hypochromic indices, elevated $\text{HbA}_2$ ($4-7\%$), and slightly elevated HbF (up to approximately $5\%$).

Why is treating a thalassemia patient with iron contraindicated?

Iron therapy will not correct red blood cell indices in thalassemia and can cause dangerous iron overload (hemochromatosis).

What skeletal deformity is seen in this patient with untreated Beta Thalassemia Major (Cooley's anemia)?

Facial bone deformities resulting from massive bone marrow expansion driven by ineffective erythropoiesis.

What is the typical hemoglobin electrophoresis pattern in a patient with Beta Thalassemia Major?

HbA is absent, HbF is markedly increased to $95-98\%$, and $\text{HbA}_2$ is elevated to $2-5\%$.

Why do patients with Beta Thalassemia Major require ongoing iron chelation therapy?

They are transfusion dependent (TDT), and repetitive transfusions combined with increased gastrointestinal iron absorption lead to fatal iron overload in major organs.

What are the genotypes and clinical names for the four stages of alpha-globin gene deletion?

1. Silent carrier: $-\alpha/\alpha\alpha$ ($1$ deletion); 2. $\alpha$ Thalassemia trait: $-\alpha/-\alpha$ or $\alpha\alpha/--$ ($2$ deletions); 3. Hemoglobin H (HbH) disease: $-/-\alpha$ ($3$ deletions); 4. Hydrops fetalis: $--/--$ ($4$ deletions).

What molecular tetramer forms Hemoglobin H, and why does it develop?

Hemoglobin H is a $\beta_4$ tetramer formed by excess unpaired $\beta$ chains due to a severe deficit of $\alpha$-globin production.

What red blood cell inclusions, giving a characteristic 'golf ball' appearance, are visualized with this supravital stain?

Precipitated Hemoglobin H ($\text{Hb H} / \beta_4$) inclusions.

What red cell inclusions visible on supravital stain represent oxidized, denatured hemoglobin clumps attached to the inner membrane?

Heinz bodies (seen in G-6-PD deficiency or thalassemia).

What tetramer forms in Alpha Thalassemia Major (Hydrops Fetalis), and what is its physiological effect on fetal oxygen delivery?

Hb Barts forms as a $\gamma_4$ tetramer ($80-90\%$); it has an extremely high oxygen affinity that prevents oxygen release to tissues, causing fatal tissue hypoxia in utero at $35-40$ weeks gestation.

What are the molecular definitions of Hb Constant Spring and Hb Lepore?

Hb Constant Spring is an elongated $\alpha$-chain variant causing a mild $\alpha$-thalassemia phenotype; Hb Lepore is a $\delta\beta$ fusion hybrid globin chain that presents clinically like $\beta$-thalassemia.