L07 - Classification and Lab Dx of anaemia Flashcards
1
Q
Where does iron absorption occur? What enhances the rate of iron transport?
A
Absorption at duodenum
Enhanced by:
- Acid, reducing agent that keep iron soluble in ferrous state
- Iron deficiency
- Enhanced erythropoiesis
2
Q
Storage and main source of iron in the body?
A
Normal turnover of senescent or defective RBC through phagocytosis in macrophages of liver, BM and spleen
Stored as ferritin, haemosiderin
3
Q
List some major and minor causes of iron deficiency?
A
Major: BLOOD LOSS: Gastrointestinal (e.g. bleeding from peptic ulcer / carcinoma of colon) Uterine Urinary Respiratory tracts (less common)
Minor/ Less common:
Increased demand (premature infants, growth spurts, multiple pregnancy);
Poor intake (dietary deficiency, mal-absorption)
4
Q
Clinical features of Iron deficiency?
A
- Asymptomatic, or;
- Anaemic symptoms and signs
- Epithelial changes
- Pica (abnormal craving to eat non-food substances)
5
Q
List some epithelial changes related to iron deficiency?
A
- Glossitis (tongue inflammation)
- Angular stomatitis
- Brittle nails
- Dysphagia
6
Q
Typical iron status finding in Iron deficiency?
A
Low serum iron (usable iron)
High serum transferrin (compensatory response to increase transport but low transferrin saturation)
7
Q
Can serum ferritin be used as a marker to identify Iron deficiency? Why?
A
No
Serum ferritin = acute phase reactant: in acute inflammation, serum ferritin level is raised
cannot indicate body iron store
8
Q
Typical PBS finding of iron deficiency anaemia?
A
- Hypochromic (no polychromasia/ reticulocytosis)
- Microcytic
- PENCIL CELLS
- Reactive thrombocytosis
- Anisopoikilocytosis: Size and shape variation (anisocytosis + poikilocytosis)
9
Q
Bone marrow examination findings in Iron deficiency anaemia?
A
Active erythropoiesis that is poorly haemoglobinised (micronormoblastic)
Decreased / absent marrow iron store
(BM exam not normally indicated for suspected iron deficiency anaemia)
10
Q
Case presentation:
68M c/o constipation
P/E: Pallor only
Normal LFT and RFT
CBC: Low MCV, MCH, MCHC Very low Hb and RBC High RDW, PLT Normal Retic
PBS:
Pencil cells, Hypochromic, Microcytic, Anisopoikilocytosis, Reactive thrombocytosis
Low serum iron, High serum transferrin, low transferrin sat.
Walk through DDx
A
- Pallor = anaemic
- Normal LFT and RFT = not likely to be sequestration or inadequate EPO stimulation
- Microcytic = Iron def. or thalassemia or anemia of chronic disease
- High RDW = Iron def. or sever thalassaemia
- Normal Retic = no reticulocytosis/ unable to perform due to raw material def.
- PBS suggest Iron def (Pencil cells)
- Iron def. anaemia = must suspect chronic bleeding, likely related to GI due to constipation, common to see colorectal cancer
11
Q
Why does retic count not rise in Iron deficiency anaemia?
A
Reticulocytosis = reactive compensation for low RBC count
Need 3 factors:
- Raw material (B12, iron, folate)
- Intact BM function
- Normal EPO
> > Iron def. = not enough Fe for reticulocytosis
12
Q
Define megaloblastic anaemia?
A
Group of anaemias: asynchronous maturation of nucleus (delayed relative to cytoplasm)
Defective DNA synthesis: usually due to deficiency of vitamin B12 +/- folate
13
Q
Metabolic pathway of folate?
A
- Absorbed dietary folates = all converted to methyl THF (= monoglutamate) by the small intestine
- transported in the plasma as THF and enters cell
- Vitamin B12 (cobalamin) is needed to convert methyl THF to THF to synthesize polyglutamate forms of folate
14
Q
List 4 causes of folate deficiency?
A
- Dietary insufficiency (e.g. poverty, elderly, alcoholics)
- Malabsorption
- Increased demand (e.g. pregnancy, haemolytic anaemia, myeloproliferative disease)
- Antifolate agents (e.g. trimethoprim, pyrimethamine, phenytoin (= anticonvulsant))
15
Q
Metabolic pathway/ absorption and transport of Vit B12?
A
- Dietary intake
- Bind to intrinsic factor secreted by gastric parietal cells
- complex is absorbed in terminal ileum
- transported in plasma via transcobalamin II: delivers to bone marrow, other tissues by receptor-mediated endocytosis
16
Q
Physiological function of folate?
A
Many biochemical reactions involving single carbon unit transfer (e.g. deoxythymidine synthesis)
17
Q
Physiological function of Vit B12?
A
Co-factor/enzyme for 2 biochemical reactions:
1) Methylcobalamin = cofactor in methylation of homocysteine to methionine by methionine synthase
2) Deoxyadenosylcobalamin = coenzyme of mutase to convert methylmalonyl CoA to succinyl CoA
18
Q
Causes of vit B12 deficiency?
A
- Dietary insufficiency (e.g. long-term vegetarians)
- Gastric causes: Prenicious anemia, Post-gastrectomy = low intrinsic factor for absorption
- Intestinal causes (e.g. stagnant loop syndrome, malabsorption syndrome, fish tapeworm) = malabsorption
19
Q
Pathogenesis of Pernicious anemia?
A
Organ-specific autoimmune disease – antibodies against:
i) Gastric parietal cells
ii) Intrinsic factor for B12 absorption
> > Cause gastric mucosa atrophy, gastric cause of Vit B12 def. and Megaloblastic anaemia
20
Q
Clinical features of Megaloblastic anaemia?
A
- Mild jaundice (lemon yellow tint)
- Epithelial changes: Glossitis, angular stomatitis
- Vitamin B12 neuropathy (complications may occur in the absence of haematological changes)
21
Q
List some clinical features under Vitamin B12 neuropathy?
A
Peripheral neuropathy*
Dementia*
Subacute combined degeneration of cord (affects dorsal and lateral columns)
Optic atrophy
22
Q
Typical PBS finding in megaloblastic anaemia?
A
Large, oval, Macrocytic RBC
Hypersegmented neutrophils (6 lobes or more)
Mild pancytopenia
23
Q
Typical BM findings in megaloblastic anaemia? When is it performed?
A
- hypercellular marrow, hyperplastic but megaloblastic erythropoiesis
- megaloblasts, giant metamyelocytes and band forms
BM exam performed if blood film does not show characteristic dysplastic features
24
Q
Typical biochemical findings for megaloblastic anaemia?
A
- Metabolic assay: raised methylmalonic acid and homocysteine levels
- Serum: Indirect hyperbilirubinaemia, increased LDH
25
How to determine if megaloblastic anaemia is caused by Vit B12 or Folate def.?
- Consider clinical features and Medical Hx
- Serum B12 assay/ Serum and RBC folate assay
- Check for upper or lower GI causes (pernicious anaemia, malabsorption...etc)
- Check for autoAb (pernicious anaemia): Anti-parietal cell or Anti-intrinsic factor
26
Interpret and walk through DDx:
72F, PMH of DM, HT
```
CBC:
Mild pancytopenia
Severe anemia
High MCV, RDW
Normal retic
```
High LDH, slight high bilirubin
PBS:
Hypersegmented neutrophils + Oval, macrocytic RBC
Active B12 low
Serum folate normal
High MCV:
- Aplastic anaemia/ BM defect
- Megaloblastic anaemia
- Severe haemolysis
- Myelodysplasia
High LDH = haemolysis or premature breakdown
Normal retic: not raised despite severe anemia. Problem with reticulocytosis?
Raw material, BM, EPO?
Raw material missing + Macrocytic + high LDH = suspect megaloblastic or severe haemolysis
PBS: definitive features of megaloblastic anaemia
Active B12 low = B12 def. causing megaloblastic anaemia + low raw material for reticulocytosis
27
Define hemolytic anemia?
Caused by:
1. Increased/accelerated red cell destruction above its normal rate, shorten RBC life span
2. Failed marrow compensation
28
Endogenous and pathogenic types of haemolysis?
1. Extravascular haemolysis: macrophages, monocytes in the reticuloendothelial system (liver, spleen) remove damaged / defective red cells from the circulation
2. Intravascular haemolysis occurs in the vasculature: pro thrombotic states i.e. shearing by mechanical heart valves, microangiopathic haemolytic anaemia (TTP)
Extravascular hemolysis split into intra-/extracorpuscular
29
Haemolytic anaemias can be classified as?
1. acquired or hereditary
| 2. intracorpuscular or extracorpuscular
30
List causes of hereditary haemolytic anaemia?
All intracorpuscular defects
Abnormal membrane, metabolism, haemoglobin
31
List major causes of acquired haemolytic anaemia? Divide into immune and non-immune causes?
All extracorpuscular defects:
a) Immune haemolysis:
i) Alloimmune (HDN, transfusion)
ii) Autoimmune (AHA)
iii) Drug induced
b) Non- immune
i) Mechanical damage (microangiopathic haemolytic anaemia, prosthetic valves)
ii) Toxin
iii) Infection
iv) Burn
(Paroxysmal nocturnal haemoglobinuria (Extremely rare))
32
List 5 lab investigations for haemolytic anaemia?
1. Markers of Hemolysis + Total and unconjugated bilirubin (increased)
2. PBS: see RBC damage + compensatory erythropoeisis (polychromasia)
3. BM exam: erythroid hyperplasia
4. Intravascular haemolysis: Haptoglobin complexes, methae-albumin, Haemoglobinaemia, Haemoglobinuria
(5. Red cell survival by 51Cr labelling)
33
List some abnormal RBC shapes and cause?
Hereditary spherocytosis: spherocytes
Sickle cell anaemia
Microangiopathic haemolysis: schistocytes
Target cell= B-thal
Elliptocyte/ Pencil cell = Iron deficiency anemia
Acanthocyte= liver disease, asplenism
Crenation = Liver disease
34
In intravascular haemolysis, haemoglobin released in plasma is dealt with in what ways?
1. Haptoglobin takes up haemoglobin to form large complex molecules: Cannot pass through renal glomeruli and excreted in urine
>> Decrease Level of free haptoglobin
2. Haptoglobin saturated: Hb bind to albumin to form methaem-albumin
3. Methaem-albumin saturation:
Haemoglobinaemia, Haemoglobinuria, (advanced = haemosiderinuria)
35
Cause of haemosiderinuria?
Renal tubules absorb some haemoglobin: iron converted to haemosiderin
>> re-excreted in urine inside dislodged renal tubular epithelial cells
>> haemosiderinuria
sign of chronic intravascular haemolysis
36
Inheritance, Pathogenesis of hereditary spherocytosis?
Usually Autosomal Dominant inheritance
Membranopathy**
- Abnormally increased membrane Na permeability, normally compensated by Na-ATP pump
- But Low pH, low glucose in spleen environment cause pump failure
>> Dysfunction of membrane proteins, membrane loss, decrease SA:Vol
>> Can't pass through spleen circulation
37
Presenting features of hereditary spherocytosis?
Jaundice
Splenomegaly
Anaemic symptoms
38
Lab tests and expected results for Dx of hereditary spherocytosis? *PBS, DAT, Flow, BM?*
- PBS spherocytes, reticulocytosis with BM erythroid hyperplasia, High MCHC
- Coombs' test negative
- Flow cytometry: reduced EMA binding to Band 3 protein
- Family Hx and +ve presentation
39
Inheritance, pathogenesis of G6PD deficiency?
X-linked recessive, males affected
G6PD with decreased catalytic activity or decreased stability = cannot make enough NAPDH through Pentose Phosphate Pathway
Low NADPH = Low GSH to protect RBC from oxidative damage
40
Lab Dx of G6PD def.?
1. Screening test (qualitative):
absence of fluorescence on NADPH in UV light/ failure to reduce methaemoglobin.
2. G6PD assay (quantitative): Confirms the diagnosis
41
What conditions can mask G6PD def.?
presence of reticulocytosis or recent blood transfusion
42
Antibodies that cause Immune haemolytic anaemia can be divided into which classes?
1. Autoantibodies: Warm or cold type, mostly idiopathic associated with underlying autoimmune diseases
2. Alloantibodies: HDN or haemolytic transfusion reaction, due to previous sensitization
3. Drug induced immune haemolytic anaemia
43
Subtypes of drug induced immune haemolytic anaemia?
a. hapten mechanism : antibody directed against drug-cell membrane complex
b. immune complex mechanism: drug-antibody complex on red cell surface causes complement deposition
c. autoimmune haemolytic anaemia
44
Describe Coombs' antiglobulin test and what type of anaemia returns positive results?
Positive in autoimmune haemolytic anaemia (AIHA)
Test Ab coated on RBCs
Rabbit IgG with antihuman globulin specificity bind to Fc portion of human IgG on red cells = agglutination
45
General Pathogenesis of Thalassaemia?
Hemoglobinopathies: Genetic disorder of globin chain synthesis
>> Imbalance in number of normal chains
>> Excess chains polymerise and precipitate
>> early destruction of RBC precursor in BM or shorten lifespan
>> Hypochromic, Microcytic RBC
46
Pathogenesis of α-thalassaemias?
Defective alpha- globin chain: 90% defect due to DNA deletion**
In foetus: excess γ chains form γ4 tetramers (Hb Bart's hydrops fetalis)
In adults: excess β chains form β4 (Hb H), α thalassaemia trait
47
What is the spectrum of α- thalassaemias?
1. Single or 2- gene deletion = α thalassaemia trait
2. 3- gene deletion = Hb H disease
3. 4 gene deletion = Hb Bart's hydrops fetalis
48
Clinical presentation and changes to RBC in α thalassaemia trait ?
Single α gene deletion = clinically/ haematologically silent, asymptomatic
2 gene deletion = Normal or slightly reduced Hb with increased RBC count. Hypochromic, microcytic RBC
49
Presentation of Hb H disease?
3 gene deletion:
Imbalance of chain production = chronic anaemia
Excess Beta chains polyermize to form Hb H (5%-40%)
Symptoms:
- Asymptomatic, or;
- Anaemia (exacerbated by infection, pregnancy)+ Splenomegaly
- Mostly normal development
50
Treatment of Hb H disease?
Generally not transfusion dependent
Common = hypersplenism, require splenectomy
51
Presentation of Hb Bart's Hydrops fetalis?
No alpha chain is found: Excess γ-chains produced in foetal period polymerise to form Hb Bart's (γ4)
Clinical presentation:
- Anaemia, Heart failure, edematous fetus
- Liver dysfunction
52
How to Dx and prevent Hb Bart's hydrops fetalis?
Dx:
- Ultrasound
- Confirm with prenatal genetic dx
Prevention:
- Public health education
- Antenatal, prenatal dx
- Detect carrier and genetic counselling
53
Pathogensis of general β-thalassaemias?
Reduced (β+) or absent (βo) synthesis of β-globin chain
Majority caused by point mutations (vs a-thalassaemia caused by gene deletion)
54
Why does the clinical presentation of β-thalassaemias occur after birth?
β-chain production becomes predominant only in post-natal period
>> severe form (β-thalassaemia major) manifests only when the patient is 3 months old or later
55
What is the spectrum of β-thalassaemias?
1. Individuals heterozygous for βo or β+ thalassaemia
= Heterozygous β- thalassaemia trait (β-thalassaemia minor)
2. symptomatic but milder clinical course than β-thalassaemia major = β-thalassaemia intermedia
3. Total absence / marked reduction of β-globin chains = β-thalassaemia major (Cooley’s anaemia)
56
Clinical presentation of β-thalassaemia minor? CBC finding, dominant Hb type?
- typically asymptomatic, slightly reduced Hb
- Reduced MCV, MCH with elevated RBC count
- Single most important diagnostic feature = raised level of Hb A2 (4-7%)*****
- Many have minor elevations of Hb F (1-3%)
57
Detailed pathogenesis of β-thalassaemia major?
Total absence / marked reduction of β-globin chains
>> excessive α-globin chains precipitate out in red cell precursors
- Ineffective erythropoiesis and extensive intramedullary destruction cause BM expansion
- Increased destruction of peripheral RBC, excpet high level of Hb F
58
Which type of Hb predominates in B-thalassaemia major?
Complete absence of Hb A
Small amounts (~2%) of Hb A2
Remainder (~98%) = Hb F
59
Blood smear finding in B-thalassaemia major?
Marked red cell anisopoikilocytosis
Most red cells = very hypochromic
Many Circulating nucleated RBC
60
Clinical presentation of B-thalassaemia major?
Typical thalassaemic facies: chipmunk-like cheeks and a prominent forehead.
Protuberant abdomen (hepatosplenomegaly)
Poor musculoskeletal development
61
What are the 3 genetic modifiers of B-thalassemia major severity?
1. Nature of β-globin gene defect (i.e. whether the mutation is associated with a severe phenotype)
2. Genetic determinants of Hb F level
3. Configuration of α-globin gene locus (affects degree of α and β globin gene imbalance)
62
Complication and treatment of B-thalassaemia major?
Complications:
- Recurrent infections, spontaneous fracture, Hypersplenism, Leg ulcers, Extramedullary haemopoiesis
Treatment = Blood transfusion dependent + Iron chelation therapy
63
Difference between pathogenesis of Warm and Cold AIHA?
Warm:
- auto-Ab IgG on RBC -> reticulo-endothelial system
- AutoAb bind to RBC best at 37 degrees
Cold:
- auto-Ab IgM on RBC -> fix C3d complement causes RBC lysis by MAC-> intravascular haemolysis
- AutoAb bind to RBC best at 30 - 32 degrees
64
What causes Warm vs Cold AIHA?
Warm: idiopathic , drugs (e.g. Methyldopa), autoimmune disease, Chronic lymphoid proliferative disease
Cold: chronic lymphoproliferative disorders (CLPD), Infection i.e. mycoplasma
65
What is the RBC likely to be coated with in Warm vs Cold AIHA?
Warm = IgG coating spherocytes
Cold = C3d (complement system) causing cold agglutination
Use Direct Antiglobulin Test to confirm presence of Ig/ complement on RBC
66
Does DAT +ve = AIHA?
No
- only showed Ab/complement coated on RBC
- Occurs in small no. of healthy people and hospitalized patients
DAT +ve only proves haemolysis is immune mediated:
Alloimmune, Autoimmune, Drug- mediated
67
Why is MCV sometimes normal in Haemolytic anaemia even if there is severe RBC destruction?
Mostly reticulocytes
Increased detroyed RBC fragments + reticulocyte volume = average normal
68
What are the 2 forms of TTP?
Thrombotic thrombocytopenic purpura (TTP) (under microangiopathic haemolytic anaemia)
* Acquired form: idiopathic, autoimmmune diseases, pregnancy, drugs, HIV infection, malignancies
* Familial form: ADAMTS13 mutation leading to enzyme deficiency
69
Symptoms of TTP?
```
fever
fluctuating neurological signs
impaired renal function
red cell fragmentation
thrombocytopenia
```
70
Pathogenesis of TTP?
Increased Von Willebrand Factor not under control of ADAMTS13 protease (hereditary defect)
Increased platelet plugging in microcirculation >> RBC traumatized (acquired)
71
Treatment of TTP?
Plasma exchange with fresh frozen plasma to remove autoantibodies, ultra-large VWF multimers and to replace ADAMTS13
Dont give platelet transfusion to patient with severe thrombocytopenia >> Attract to VWF massively and worsen
72
What disease must be considered as a DDx if anaemia and thrombocytopenia is present?
Microangiopathic haemolytic anaemia
