Hemoglobin AS Disease (Sickle Cell Trait)
The AS phenotype is heterozygous for the sickle mutation. Most of the time, patients are asymptomatic.
Exception: Severe hypoxia can trigger sickling and hemolysis even in trait carriers.
Inheritance: Autosomal recessive — both alleles must be affected for homozygous disease.
Alpha Thalassemia: The Gene Picker
Alpha thalassemia is caused by GENE DELETIONS (not point mutations). Humans have 4 alpha-globin genes. Each gene = 25% of normal hemoglobin production.
Common in: Mediterranean, African, Southeast Asian populations. Inheritance: Autosomal recessive.
Interactive Gene Picker: Delete Genes and See the Result
Click on an alpha gene to delete it. Watch how hemoglobin levels and clinical status change:
Alpha Thalassemia Minor
| Genes Deleted | Frequency | Sedentary | Active | Hb Level |
|---|---|---|---|---|
| 1 gene (3 remaining) | 75% | Asymptomatic | Asymptomatic | ~12 g/dL |
| 2 genes (2 remaining) | 50% | Asymptomatic | Symptomatic | ~7.5 g/dL |
| 3 genes (1 remaining) | 25% | Symptomatic | Symptomatic | 4-5 g/dL |
Alpha Thalassemia Major (All 4 Genes Deleted)
0 genes remaining = unable to make ANY hemoglobin. All hemoglobin types require alpha chains.
Result: hydrops fetalis — congestive heart failure in utero. 🔑 Fetus can't make functional hemoglobin, cardiac output fails, massive fluid accumulation, incompatible with life.
Hb Barts (γ4 chains): NOT allosteric, cannot release oxygen to tissues.
HbH (β4 chains): NOT allosteric, precipitates into Heinz bodies.
Baseline labs: RBC 3.5-4.5 million, Hb/Hct 15/45%
Beta Thalassemia: Compensation Strategy
Beta thalassemia involves 2 beta-globin genes (one per chromosome). When beta genes are deleted, the body compensates by making MORE HbA2 and HbF.
Problem: HbF becomes useless after 6 months of age.
Beta Thalassemia Minor (One Gene Deleted)
Hb ~7.5 g/dL
- Sedentary = asymptomatic
- Active = symptomatic
- Increased HbA2 and HbF on electrophoresis
- Ineffective erythropoiesis — bone marrow working overtime
Beta Thalassemia Major (Both Genes Deleted)
Body can ONLY make HbA2 and HbF.
- Asymptomatic until 6 months (while HbF is still functional)
- Then HbF becomes useless — hemoglobin crisis
- Transfusion dependent for life
Blood Products: The Catalog
Click each card to flip and see the clinical use. 9 products you need to know:
Transfusion Principles
Transfuse only when symptomatic. Target hemoglobin depends on context:
- Heart failure: Keep Hb 10-12 g/dL
- Renal failure: Keep Hb 10-12 g/dL
1 unit PRBCs raises Hb by 1-2 grams (HCT by 3-6) and delivers 3.4g iron.
If reticulocyte count is highHigh retic = bone marrow is already compensating and producing RBCs, let the bone marrow handle it — no transfusion needed.
Any foreign protein transfusion = risk of allergic reaction.
Transfusion Reactions: The Board Traps
Anaphylaxis
Cause: Selective IgA deficiency in recipient. Patient develops anti-IgA antibodies.
Management: STOP transfusion, epinephrine, use IgA-filtered blood for future transfusions.
Acute Febrile Reaction
Cause: WBC antigens in donor blood trigger fever.
Management: Supportive care, premedicate with acetaminophen for future transfusions.
ABO Incompatibility
Most common transfusion reaction. Cause: Wrong blood type given.
Management: STOP transfusion immediately, re-type and cross-match, supportive care.
TRALI (Transfusion-Related Acute Lung Injury)
Cause: Cytokine release from donor leukocytes.
Presentation: ARDS picture (bilateral infiltrates, hypoxemia within 6 hours of transfusion).
Management: Steroids, mechanical ventilation if needed.
TACO (Transfusion-Associated Circulatory Overload)
Cause: Transfusing too fast into elderly or renal failure patients.
Management: Vigorous diuresis.
Iron Overload & Hemochromatosis
From Transfusions to Iron Poisoning
Multiple transfusions → iron overload. Why? RBCs contain heme iron, body has no excretion mechanism.
Hemosiderosis: Bone marrow overwhelmed by iron deposits.
Hemochromatosis: Iron spills into OTHER organs. 🔑 "Bronze" organs — skin gets bronze pigmentation, liver gets cirrhosis, pancreas gets diabetes, heart gets restrictive cardiomyopathy, joints get arthritis.
Organ Involvement (The "Bronze Triad")
| Organ | Manifestation | Clinical Pearl |
|---|---|---|
| Skin | Bronze pigmentation | Early sign |
| Liver | Bronze cirrhosis | Fibrosis → cancer |
| Pancreas | Bronze diabetes | Insulin resistance |
| Heart | Restrictive cardiomyopathy | Can be fatal |
| Joints | Arthritis (MCP 2-3) | Painful |
Treatment
Chelating agents: Deferoxamine, penicillamine, EDTA-BAL
Primary Hemochromatosis
Autosomal recessive. Cause: Too much iron absorption from duodenum. Associated with HLA A3 on chromosome 6.
Secondary Hemochromatosis
Cause: Too many transfusions (like in thalassemia major).
Most common cause of death in first 10 years: Infections (iron supports bacterial growth)
Most common cause of death after 10 years: CHF (iron cardiomyopathy)
Diagnostic Clue
Stain for iron usingPrussian blue binds ferric iron (Fe³⁺), turning it blue under microscopy PRUSSIAN BLUE.
Transfusion-Related Infections
Blood transfusions expose recipient to: HIV, Hep B/C/D, EBV, CMV, hemorrhagic viruses, bacteria, malaria, babesiosis, syphilis.
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