megaloblastic anemia

1. MEGALOBLASTIC
ANEMIA
Dr. Anshita Dubey

2. Megaloblastic anemia is caused by impaired
DNA synthesis due to lack of B12 or folic acid.

3. ABSORPTION OF FOLIC ACID
POLYGLUTAMATES
↓ folate hydrolase (proximal jejunum) Zn
MONOGLUTAMATES
↓
PTEROYLGLUTAMATE
↓ folate carrier (pcft)
LUMINAL CELL
↓
5 METHYLTETRAHYDROFOLATE
↓ mrp 3
PORTAL CIRCULATION

4. CAUSES

5. IMPAIRED ABSORPTION
 NON TROPICAL SPRUE
 TROPICAL SPRUE

6. INCREASED REQUIREMENT

7. FOLIC ACID ANTAGONISTS
 METHOTREXATE
 6 MERCAPTOPURINE
 CYCLOPHOSPHAMIDE
INHIBIT DIHYDROFOLATE REDUCTASE

8. ABSORPTION OF B12
COBALAMINE (RELEASED FROM FOOD BY PEPSIN)
↓
COMBINES WITH TRANSCOBALAMIN I/HAPTOCORRIN
(R BINDER)
↓ pancreatic enzymes
RELEASE OF COBALAMIN
↓
BINDS TO IF

9. IF COBALAMIN COMPLEX + CUBAM (ileum)
(cubilin+amnionless)
↓ endocytosis
ILEAL CELL
↓ cobalamin released
BINDS TO TRANSCOBALAMIN
↓
EXPORTED TO PORTAL CIRCULATION
Haptocorrin bound cobalamin-reservoir (70-90%)
Transcobalamin bound-5%

10.  Daily intake : 2-5 µg/day
 Body stores : 2-5 mg
 DAILY EXCRETION IN BILE - 1.4µg/day
 DAILY REABSORPTION - 1µg/day

11. CAUSES OF B12 DEFICIENCY

14. CLINICAL FEATURES

16. HEMATOLOGICAL FINDINGS
ABSOLUTE VALUES :
MCV : RAISED (110-130)
MCH : RAISED
MCHC : NORMAL
Hb : reduced
HEMATOCRIT : DECREASES
RETICULOCYTE COUNT : NORMAL/ ↓
WBC : ↓
PLATELET : ↓
MEAN PLATELET VOLUME : ↓
INCREASED PLATELET ANISOCYTOSIS

17. PERIPHERAL SMEAR

19. BONE MARROW PICTURE

20.  Hyperplastic marrow
 erythroid precursors(megaloblasts) : ↑
 Myeloid erythroid ratio : ↓
 delicate chromatin - more “open” chromatin pattern in erythroid
precursors
 Giant metamyelocyte
 Megakaryocytes are large and have separated nuclear lobes or nuclear
fragment.
 Transfused patients: number of erythroid precursors diminishes but the
cytologic abnormalities persist

22.  HYPOGRANULAR NEUTROPHILS AND MONOCYTOSIS : MDS
 Subclinical folate and cobalamin deficiency : Increased plasma
homocysteine and serum methyl malonic acid.

23. BIOCHEMICAL PARAMETERS
COBALAMIN
normal values:200-900ng/l
 MICROBIOLOGICAL ASSAY – Euglena gracilis
Functional assay
Measure the ability of the test serum to stimulate growth of
an organism.
microbiological growth is directly proportional to the vitamin
content of the serum

24.  RADIOISOTOPIC DILUTION &
 CHEMILUMINESCENCE ASSAYS

25. LOW COBALAMN LEVELS: HIV infection or multiple
myeloma and those receiving megadose vitamin C therapy
Spuriously normal cobalamin :
 cobalamin deficiency associated with overgrowth of
intestinal bacteria (produce biochemically inert B12
analogs)
 autoimmune disorders
 myeloproliferative neoplasms
 active liver disease

26. Holotranscobalamin
fall below the normal range long
before total serum cobalamin.
represent a state of negative
cobalamin balance.

27. adenosylcobalamin
 Methylmalonate succinate
methylmalonylcoA mutase
Urine excretion of methylmalonate – cobalamin deficiency
Other causes: methylmalonic aciduria
chronic renal failure

28. METHYLMALONATE LEVELS
 Gas chromatography mass spectometry

29. HOMOCYSTEINE LEVELS
 High performance liquid chromatography
 Commercial enzyme immunoassays

30. SCHILLING TEST
0.5 to 2.0 μg of radioactive cobalamin is orally administered
↓ 2 HOURS
Flushing dose of nonlabeled cobalamin is given parenterally
more than 7% of LESS THAN 7%
ingested cobalamin in the urine
in 24 hours
( NORMAL) ( LACK OF IF)

31.  Deoxyuridine Suppression Test: (OBSOLETE)
tritium-labeled thymidine
(3H-Tdr) is incorporated into DNA
↓
In megaloblastic marrows deoxyuridine cannot be efficiently
converted to thymidine
↓
more 3H-Tdr is taken up into DNA
↓
cobalamin and folate deficiency

32. If excretion is low
↓
hog IF orally along with labeled cobalamin
Normal 24 hour excretion Remains abnormal
↓ ↓
IF DEFICIENCY malabsorption due to
intestinal disease
Test to be repeated after 7-10 days of antibiotic therapy if bacterial
overgrowth syndrome is suspected
Pancreatic extracts may be added to investigate the possibility of
pancreatic dysfunction

33. Serum and Red Cell Folate
 A microbiological assay for folic acid activity -
Lactobacillus casei
 Radioisotopic
 chemiluminescence methods
Serum - 5-methyltetrahydrofolate
red cell - heterogeneous mixture of different forms with
varying polyglutamate chain lengths.

34.  The measurement of folate in red blood cells (RBCs) is
preferred since it reflects long-term folate status in the
body compared to plasma/serum folate which may be
influenced by recent dietary intake

35. fresh whole + freshly prepared 1% ascorbate
↓
Incubate at 37 ºC for 20 min
↓
converts RBC folate polyglutamates to assayable folates

36. ECLIA
25µl serum + pretreatment reagent 1 and 2
↓
Bound folate released from endogenus binding protein
↓
Incubate with ruthenium labelled folate binding protein
↓
folate complex

37. Add streptavidin coated microparticles and folate labelled with
biotic
↓
Ruthenium labelled folate binding protein-folate biotic
complex
Amount is proportional to the analyte concentration in the
sample
Reference range : 4.6-18.7ng/ml

38. BCSH RECOMMENDATIONS
 A blood film showing oval macrocytes and hypersegmented
neutrophils in the presence of an elevated MCV - suspect
cobalamin or folate deficiency.
 Cobalamin and folate assays should be assessed concurrently due
to the close relationship in metabolism.
 A serum cobalamin cut-off level of either 148 pmol/l (200 ng/l)
should be used as evidence of cobalamin deficiency in the presence
of a strong clinical suspicion.
 The report providing the result of a serum cobalamin assay should
include the following:

39.  The interpretation should be considered in relation to the
clinical circumstances.
 Falsely low serum cobalamin levels may be seen in the
presence of folate deficiency.
 Neurological symptoms due to cobalamin deficiency may
occur in the presence of a normal MCV.
 Plasma Hcy and/or plasma MMA, depending on availability,
be considered as supplementary tests to determine
cobalamin deficiency in the presence of clinical suspicion of
deficiency but an indeterminate serum cobalamin level.
 plasma Hcy - sensitive marker; plasma MMA - more

40. HoloTC is suggested as a suitable assay for
assessment of cobalamin status
Currently there is no ‘gold standard’ test for
diagnosis of cobalamin deficiency