Course title :Hematology (1)Course code:MLHE-201Supervisor :Prof Dr.Magda SultanDate : 12/12/2013

Outcome:The student will be able to know :-Definitions of megaloblastic and non-megaloblastic anaemias.-How to diagnose these anaemias ?.- What are their causes ?

Megaloblastic anaemia

• Macrocytic anemias are characterized by large RBCs with a normal hemoglobin content.

• Macrocytic anemias are classified as either megaloblastic or non-megaloblastic– Megaloblastic anemias are associated with

defective DNA synthesis and therefore, abnormal RBC maturation in the bone marrow (a nuclear maturation defect).

– In megaloblastic anemias, the granulocytic and megakaryocytic maturation are also affected and this leads to pancytopenia

The biochemical basis for this is as follows: Megaloblastic dyspoiesis (abnormal synthesis)

occurs when the DNA synthesis in the hematopoietic system is disrupted or slowed down.

Other rapidly proliferating cells in the body are also affected.

Administration of drugs that interfere with DNA metabolism can be the cause of a megaloblastic anemia.

On rare occasions there is an inherited disorder that affects DNA synthesis

However, the primary defect in DNA replication is usually due to depletion of thymidine triphosphate which leads to retarded mitosis, and therefore retarded nuclear maturation. Vitamin B12 deficiency is usually due to a deficiency of a factor necessary for B12 absorption while a folic acid deficiency is usually due to an inadequate dietary intake.

The depletion of thymidine triphosphate is usually due to a deficiency of vitamin B12 or folic acid.

Absorption and metabolism of vitamin B12 and folic acid:Vitamin B12 (cyanocobalamine): - Is found in meats, eggs, dairy products, and liver.- Is absorbed via a binding protein called intrinsic factor (IF)

Vitamin B12 and IF bind to mucosal cells in the ileum and B12 enters.

When B12 is released from the mucosal cell, it binds to transport proteins in the blood stream (transcobalamine IIII). Type II is the primary transport protein. Therefore a congenital deficiency in type II can lead to a megaloblastic anemia.

B12 is transported to the bone marrow for use or to the liver for storage.

VITAMIN B12 ABSORPTION

HOW IS B12 INVOLVED IN DNA SYNTHESIS?

MEGALOBLASTIC ANEMIASDecreased vitamin B12 therefore results in no conversion of N5-methyl THF to THF. Thus, the net result is that dTMP for DNA synthesis is not made.

Humans need 3-5 ug of vitamin B12 per day. Since 70% of dietary B12 is absorbed, the diet needs to contain 5-7 ug/day.

MEGALOBLASTIC ANEMIASFolic acid (pteroyl glutamic acid)

Is found in most foods, including eggs, milk, yeast, and liver.

Is abundant in green, leafy vegetables and is synthesized by many microorganisms.

Is destroyed by heatAbsorption occurs in the small intestine

HOW IS FOLIC ACID INVOLVED IN DNA SYNTHESIS?

MEGALOBLASTIC ANEMIAS» Therefore, with decreased folic acid, the net result is the

same as that for decreased vitamin B12 – there is decreased conversion of dUMP to dTMP, and thus, dTTP which is required for DNA synthesis.» Defective DNA synthesis may occur when dUTP gets

used in place of dTTP because there is a great increase in erroneous DNA copying where dUTP is put in place of dTTP.» Humans need to get about 50 ug/day of folic acid from

the diet

Causes of megaloblastic anemia -Vitamin B12 deficiency

» 85% is due to lack of intrinsic factor (IF) secondary to gastric atrophy – this is called pernicious anemia (PA) and it occurs most often in older adults (over 40), most commonly in individuals of Northern European descent, and more commonly in women. Antibodies against the parietal cells in the G.I. tract and against IF are commonly found in these individuals.» After gastrectomy»Malabsorption syndrome» Inadequate dietary intake (rare)» Defective or absent transport proteins (transcobalamine)

MEGALOBLASTIC ANEMIASFolic acid deficiency

Inadequate diet is the major cause and this occurs most often in the poor, elderly, and alcoholics.

When there is increased requirement such as in pregnancy, hemolytic anemia, leukemia, etc.

Malabsorption – may be due to diseases of the upper small intestine such as ileitis, tropical sprue, and gluten sensitive enteropathy.

When there is increased loss such as in patients undergoing hemodialysis

Drug inhibition – examples are oral contraceptives, anticoagulant drugs, alcohol, and isoniazid

MEGALOBLASTIC ANEMIAS

• Clinical manifestations occur in two categories – those found in folic acid or vitamin B12 deficiency, and those mainly found in B12 deficiency– In both types of deficiency the symptoms include

pallor, weakness, a smooth, sore tongue, and diarrhea alternating with constipation– In vitamin B12 deficiency, and occasionally folic acid

deficiency, there are neurological disturbances including numbness and tingling of extremities, gait abnormalities, and mental disturbances.

MEGALOBLASTIC ANEMIASLab findings

Macrocytic, normochromic anemia (MCV=100-140, MCHC is normal))

MCH is increased (due to increased cell size)

Hemoglobin and RBC counts are decreasedWBC and platelet counts are decreasedOn a peripheral smear, a triad of things is commonly seen: oval macrocytes, Howell Jolly bodies (nuclear DNA fragments), and hypersegmented neutrophils (5 or more lobes).

MEGALOBLASTIC ANEMIASIn addition:

Anisocytosis is usually moderatePoikilocytosis is striking with nucleated RBCs, polychromatophilia, and cabot rings (spindle remnants).

RBC dimorphism is seen with concomitant IDA.

The absolute reticulocyte count is decreased because of ineffective erythropoiesis.

PERIPHERAL SMEAR OF MEGALOBLASTIC ANEMIA

• Oval Macrocyte

• Howell Jolly Body

• Cabot ring

PERIPHERAL SMEAR OF MEGALOBLASTIC ANEMIA

Hypersegmented neutrophil

MEGALOBLASTIC ANEMIAS The bone marrow will show hypercellularity,and

megaloblastic erythroid series , yet there are decreased numbers of all cell types in the peripheral blood because ineffective hematopoiesis is occurring and many cells are dying prematurely in the bone marrow.

In folic acid deficiency – there will be decreased serum and RBC folate

In B12 deficiency – there will be decreased serum vitamin B12

Specific tests for PAGastric analysis – if there is no free HCl after

histamine stimulation, this may indicate PA since the same cells that secrete HCl, also secrete intrinsic factor (IF)

Test for antibodies to IF

NON-MEGALOBLASTIC MACROCYTIC ANEMIA

NON-MEGALOBLASTIC MACROCYTIC ANEMIA

Note that the macrocytic RBCs are not oval, but are round.

There are no hypersegmented neutrophils or Howell-Jolly bodies

DIFFERENTIAL DIAGNOSIS WITH INCREASED MCV

LAB RESULTS OF MEGALOBLASTIC VS NON-MEGALOBLASTIC MACROCYTOSIS

Assignement :

• Student name : ابراهيم محمود تغريد Title: Laboratory diagnosis of macrocytic anaemias Student name : عشري محمد حمادهTitle : Types of macrocytic anaemias .Student name : نظير سدراك باخومTitle : Peripheral blood findings in megaloblastic anaemias .

• Training questions :What are the peripheral blood findings in megaloblastic anaemias ?Mention the causes of megaloblastic anaemia. -Reference Book : - Essential hematology - Dacie .