Flashcards in CH2 Deck (36):
When is Normocytic, normochromic anaemia seen?
In anaemia of chronic disease
In some endocrine disorders (hypopituitarism, hypothyroidism, hypoadrenalism)
In some haematological disorders (aplastic anaemia, some haemolytic anaemias)
Seen acutely following blood loss
Name two types of Macrocytic anaemias
(Depends on bone marrow findings)
Describe the visual features of normochromic, normocytic anaemiaa
Small pale cells with no iron
What causes the production of megaloblasts?
Erythroblasts having delayed nuclear maturation in bone marrow due to defective DNA synthesis
Describe the features of magaloblasts
Have large immature nuclei
Nuclear chromatin is more finely dispersed than normal
Giant metamyelocytes (abnormal white cells)
What is a giant metamyelocyte?
An atypical myeloid cell with clumped chromatin in a large, often bizarre, immature nucleus, and relatively mature cytoplasm.
Describe the features of giant metamyeloctes
Giant metamyelocytes are typical of megaloblasic anaemia.
Twice the size of normal cells, with twisted nuclei
What causes megaloblastic changes in giant metamyelocytes?
The changes typically occur due to B12 deficiency or metabolism, folic acid deficiency, abnormal folate metabolism of other defects of DNA synthesis, or with drugs such as AST.
What are the haematological values of Megaloblastic Anaemia?
Mean Corpuscular Volume (Average volume of the body's blood cells)>96fl
Macrocytes oval shaped
Neutrophils with hypersegmented polymorphs, >6 lobes
Bone marrow is usually hypercellular
Erythroblasts are large and show failure of nuclear maturation - maintaining an open, fine, lacy primitive chromatin pattern, but normal haemaglobinization
If severe there may be leucopenia (low WBC) or Thrombocytopenia (low thrombocytes)
What are the causes of megaloblastic anaemias?
Vitamin B12 deficiency
Abnormalities of Vit B12 or folate metabolism (E.g. transcobalamin II deficiency, nitrous oxide, antifolate drugs)
Other defects of DNA synthesis
- Congenital enzyme deficiency e.g. orotic aciduria
- Acquired enzyme deficiency e.g. alcohol, hydroxyurea therapy
Give examples of the effects of Vit B12 or folate deficiency
Macrocytosis of epithelial cell surface
Neuropathy (for vit B12 only)
Rarely, reversible melanin skin pigmentation
Decreased osteoblast activity
Neural tube defects in fetus (spina bifida)
Cardiovascular disease e.g. Stroke
Why do B12 and folate deficiency cause megaloblastic anaemia?
dUMP to dTMP is the cycle which produces your DNA.
Both Vit B12 and folate are necessary for normal synthesis of DNA.
Without B12 or folate you cannot form the methylene FH4, so the cycle of dUMP to dTMP does not occur
How long is the body's store of B12 sufficient for?
How long is the body's store of folate sufficient for?
Describe the biochemical basis of megaloblastic anaemias
Block in DNA synthesis due to inability to methylate deoxyuridine monophosphate ro deoxythymidine monophosphate used to build DNA
Other congenital & acquired forms of megaloblastic anaemia are due to interference with purine or pyrimidine synthesis, causing an inhibition in DNA synthesis
What are the causes of B12 deficiency?
Normally nutritional - Especially in vegans
- Pernicious anaemia
- A congenital lack or abnormality of intrinsic factor
- Total or partial gastrectomy
- Intestinal stagnant loop syndrome - Jejunal diverticulosis, blind loop stricture, etc.
- Ileal resection & Crohn’s disease
- Congenital selective malabsorption with proteinuria (autosomal recessive megaloblastic anaemia)
- Fish tapeworm
Why can B12 deficiency occur following a gastrectomy?
When foods containing B12 are eaten, the vitamin is usually bound to protein and is released by stomach acid. Following its release, most B12 is absorbed by the body in the small bowel (ileum) after binding to a protein known as intrinsic factor. Intrinsic factor is produced by parietal cells of the gastric mucosa (stomach lining) and the intrinsic factor-B12 complex is absorbed by cubilin receptors on the ileum epithelial cells.
In gastrectomy, either the parts of the stomach that produce gastric secretions are removed or they are bypassed. This means intrinsic factor, as well as other factors required for B12 absorption, are not available
What test is performed to check for B12 defieiceny?
Deoxyuridine suppression test
What is the procedure for Deoxyuridine suppression test?
Tritiated thymidine is added to patient’s bone marrow in vitro.
You add the thymidine to the bone marrow in your petri dish.
If you have taken up less than 5% of the thymidine that means your bone marrow is normal.
If you cells aren’t performing normally it will take more of the thymidine. In megaloblastic marrow, you will use between 5-50% of the tritiated thymidine.
Where is B12 found?
Vitamin B12 is also synthesised by micro-organisms found in the gut. It is found in meat, fish, eggs and milk, but not in plants. When cooked, the vitamin B is not normally destroyed.
How much B12 can an adult store?
2-3 mg in liver
How much B12 does an adult use daily?
How is B12 absorbed and transported?
Vitamin B12 is liberated from protein complexes in the food, by gastric enzymes. It then binds to two Vitamin B12 binding proteins:
- Intrinsic factor
- ‘R’ binder from saliva
What is intrinsic factor?
The intrinsic factor is a glycoprotein, with a Met>44000
It is secreted by gastric parietal cells with H+ ions. It combines with Vitamin B12 and caries it to the specific receptors on the mucous of ileum.
B12 then enters the ileal cells & intrinsic factor remains in lumen
How is B12 transported from the enterocytes?
Once the IF/B12 complex is recognized by specialized ileal receptors, it is transported into the portal circulation. The vitamin is then transferred to transcobalamin II (TC-II/B12), which serves as the plasma transporter.
TC II is the essential carrier protein for B12. Tamount of B12 on TC II is low, due to rapid clearance. TC II delivers coalbumin to all cells of body
Plasma bound B12 is mainly bound to transcobalamin I
(TC I) (70-90%), the functional role of which is unknown
What are the causes of folate deficiency?
Nutritional - Especially in old age, institutions (e.g. care homes), poverty and famine, special diets (e.g. goat’s milk anaemia)
Coeliac disease, partial gastrectomy, Crohn’s disease
- Physiological: pregnancy & lactation
- Pathological: Haematological disease- Haemolytic anaemias
Malignant disease: carcinoma, lymphoma, myeloma
What is the treatment for megaloblastic anaemia due B12 deficiency?
Hydroxocobalamin 1000 micrograms intramuscularly
- 5-6 mg over 3 weeks, 1000 micrograms every 3 months - rest of life
Clinical improvement within 48 hrs
- reticulocytosis seen in 2-3 days (peak 5-7d)
- White cell and platelet counts become normal in 7-10 days
- Marrow normoblastic within about 48 hours (although giant metamyelocytes persist for up to 12 days)
- Improvement of polyneuropathy over 6-12 months, however spinal cord damage is irreversable
What is the treatment for megaloblastic anaemia due to folate deficiency?
5mg folic acid orally, initially for 4 months
Maintenance depend on underlying condition (whether it requires lifelong therapy, or is a short term condition)
What is the most common B12 deficiency in adults?
Pernicious anaemia, due to malabsorption of B12.
This may be due to pancreatitis or coeliac disease.
What side effects can occur from B12 injections for megaloblastic anaemia?
What causes Pernicious anaemia?
Autoimmune attack on the gastric mucosa, leading to atrophy of the stomach. The wall of the stomach becomes thin, with a plasma cell and lymphoid infiltrate of the lamina propria. Intestinal metaplasia may occur.
As a result pf the atrophy of the gastric mucosa, there is a consequent failure of intrinsic factor production.
Describe the pathogenesis of pernicious anaemia
Common in the elderly, 1/8000 >60yrs affected UK
All races, common in fair haired, blue eyed, females
Association with other autoimmune diseases e.g. thyroid disease, Addison’s disease, vitiligo
50% of PA patients have thyroid antibodies
What are the clinical features of Pernicious Anaemia?
Insidious (progressively increasing symptoms of anaemia)
Neurological changes - irreversable
- Occur in patients with v. low levels of serum B12 <60ng/l
- Occasionally in patients not clinically anaemic
Symmetrical parathesia (numbness in fingers & toes)
Early loss of vibration sense and proprioception
Progressive weakness and ataxia
Paraplegia may result
Dementia and optic atrophy
What tests can be performed for B12 deficiency?
Whole body counting
Describe the process for the Schilling test
Patient is given radiolabeled vitamin B12 to drink or eat (58Co) after fasting.
An intramuscular injection of unlabeled vitamin B12 is given an hour later (this is not enough to replete or saturate body stores of B12).
The purpose of the single injection is to temporarily saturate B12 receptors in the liver with enough normal vitamin B12 to prevent radioactive vitamin B12 binding in body tissues (especially in the liver), so that if absorbed from the G.I. tract, it will pass into the urine. The patient's urine is then collected over the next 24 hours to assess the absorption.
A normal result shows at least 10% of the radiolabeled vitamin B12 in the urine over the first 24 hours.
In patients with pernicious anemia or with deficiency due to impaired absorption, less than 10% of the radiolabeled vitamin B12 is detected.
If an abnormality is found, i.e. the B12 in the urine is only present in low levels, the test is repeated, this time with additional oral intrinsic factor.
• if excretion normal : PA, gastrectomy
• if excretion abnormal: lesion in terminal ileum, bacterial overgrowth