MLS 2304 Unit 4: Hemoglobin Disorders, Thalassemias & Lab Interpretation

What is the major adult fraction of hemoglobin?

HbA (α₂β₂)

What hemoglobin predominates in fetal and newborn life?

HbF (α₂γ₂)

What is the structural difference between HbS and normal hemoglobin?

In HbS, valine replaces glutamic acid at beta-chain position 6.

What is the effect of dehydration on HbS?

Dehydration increases intracellular HbS concentration, promoting polymerization.

What does HbC represent in terms of amino acid change?

Beta-6 glutamic acid becomes lysine.

What is the inheritance pattern of thalassemia?

Each pregnancy is an independent event, and the probability of offspring genotypes can be calculated based on parental gametes.

What does HbAS indicate?

Sickle cell trait, usually asymptomatic with an unremarkable routine smear.

What is the typical clinical expression of severe β0/β0 thalassemia?

No endogenous HbA; markedly increased HbF; HbA₂ variable.

What is the significance of reticulocyte response in chronic hemolysis?

Chronic hemolysis usually increases reticulocytes and polychromasia; a falling reticulocyte response suggests an aplastic episode.

What is the typical morphology seen in alpha-thalassemia trait?

Marked microcytosis with no or mild anemia.

What does HPFH stand for?

Hereditary persistence of fetal hemoglobin.

What is the mechanism of ineffective erythropoiesis in beta thalassemia?

Excess unpaired alpha chains precipitate and damage cells, leading to death of erythroid precursors.

What is the typical laboratory finding in HbH disease?

Presence of unstable tetramers (β₄) that can precipitate and cause hemolysis.

What is the role of hydroxyurea in sickle cell disease?

Hydroxyurea can increase HbF and mean corpuscular volume (MCV).

What is the expected hemoglobin pattern in beta trait?

HbA predominates; HbA₂ usually increased; HbF normal or mildly increased.

What is the typical clinical presentation of HbSS?

Commonly produces hemolytic anemia, reticulocytosis, sickle cells, target cells, and polychromasia.

What does HbSC indicate?

Compound heterozygous sickle cell disease, not sickle trait.

What is the consequence of high oxygen affinity hemoglobin?

It impairs unloading and can cause erythrocytosis.

What are Heinz bodies?

Precipitated hemoglobin forms that can occur in unstable hemoglobins.

What is the significance of Howell-Jolly bodies?

They indicate impaired splenic function and increased infection risk.

What is the mechanism of HbM?

Ferric iron (Fe3+) produces methemoglobinemia and cyanosis.

What does β+ allele indicate?

Reduced beta-chain production from that allele.

What does β0 allele indicate?

No beta-chain production from that allele.

What is the typical finding in severe disease with residual beta synthesis?

HbA reduced and variable; HbF increased.

What is the expected outcome of transfusion in thalassemia?

Transfusion introduces donor hemoglobins and can affect laboratory findings.

What is the clinical significance of target cells?

Target cells are often associated with hemoglobinopathies and thalassemias.

What is the typical morphology of microcytic anemia?

Small RBCs with low hemoglobin concentration.

What is the effect of stop-codon readthrough in Hb Constant Spring?

It results in an elongated alpha chain.

What can a present gene indicate about functional output?

It can still have reduced functional output.

How do nondeletional HbH combinations compare to common deletional disease?

Some nondeletional HbH combinations are more severe.

What is a typical finding in iron deficiency?

Reduced RBC count.

What is a typical finding in thalassemia trait?

RBC count is often preserved or increased.

What does low ferritin indicate?

It supports iron deficiency.

What is the HbA₂ level in beta thalassemia trait?

Usually increased.

What is the HbA₂ level in alpha thalassemia trait?

Normal or reduced.

What does normal adult fractionation indicate?

It does not exclude alpha trait.

What does a positive solubility test indicate?

It cannot distinguish trait from disease.

What complicates detection in solubility tests?

High HbF in infancy, severe anemia, low HbS concentration, and recent transfusion.

What does separation in electrophoresis not represent?

It is not genotype.

What does capillary zone electrophoresis separate by?

Charge and mobility.

What does HPLC use for separation?

Chromatographic behavior.

What is the formula for calculating MCV?

Hct (%) × 10 / RBC = fL.

What does MCH measure?

Average hemoglobin mass per cell.

What does MCHC measure?

Hemoglobin concentration within RBCs.

What is the significance of a preserved RBC count with microcytosis?

It is a clue, not a diagnosis.

What does a negative limited genetic assay indicate?

It does not exclude every variant.

What factors can change expected findings in hemoglobin disorders?

Age, transfusion, treatment, residual chain synthesis, and coexisting disorders.

What is the 1₂s rule in quality control?

One result beyond +2 or −2 SD is a warning, not automatic rejection.

What does the 10x rule in quality control indicate?

Ten consecutive results on the same side of the mean lead to rejection.

What should be done if QC is rejected?

Hold affected reporting, investigate the cause, and verify acceptable performance.

What is the importance of connecting inherited changes to laboratory patterns?

It helps trace the biological sequence from globin product to cell injury.

What does the term 'ineffective erythropoiesis' refer to?

It can increase iron burden even without regular transfusion.

What does a patient delta alert compare?

Current and previous results.

What is the role of molecular studies in hemoglobin disorders?

They address sequence or copy-number changes.

What is the significance of coelution in HPLC?

It can affect HbA₂ measurement limitations depending on the platform.