Why B12/Folate deficiency causes macrocytosis (cells larger than normal)?
Both vitamin B12 and folate are essential for DNA synthesis. Defective DNA synthesis (due to a deficiency in either) results in the nucleus maturing at a slower rate than the cytoplasm, in a process called nucleo-cytoplasmic asynchrony. This leads to fewer cell divisions, thereby producing a red cell that is larger than normal (macrocyte).

Normally, neutrophils have 3-4 (rarely 5) lobes.

Never treat megaloblastic anemia with folate before making sure the patient doesn't have B12 deficiency

If a patient has B12 deficiency and you administer folate, this will effectively treat the anemia, but not the neuropathy. And this could mask the neuropathy, delay its diagnosis, and cause more severe (or irreversible) damage to the nervous system.

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الـ Direct يستخدموه عادةً حتى يشوفون إذا الشخص عنده hemolysis لو لا (autoimmune hemolysis مثلًا).

الـ Indirect غرضه هو screening & prevention بالدرجة الأُولى.

There are some general features of hemolysis and other specific features that help to identify the reason for hemolysis. General features of hemolysis are:

• Decreased hemoglobin level.
• Increased unconjugated bilirubin.
• Increased LDH. This is because RBCs lack mitochondria and must rely on anaerobic respiration to obtain energy.
• Increased reticulocyte count.

The red cells may give an indication of the likely cause of the hemolysis:

• Spherocytes are small, dark red cells that suggest autoimmune hemolysis or hereditary spherocytosis.

• Sickle cells suggest sickle-cell disease.

• Red cell fragments (schistocytes) indicate microangiopathic haemolysis, such as TTP, DIC, and HUS.

• Bite cells (normal-sized red cells that look as if they have been partially eaten) suggest oxidative hemolysis. They contain Heinz bodies, which attract macrophages to eat them.

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The compensatory erythroid hyperplasia may give rise to folate deficiency, with megaloblastic blood features.

March hemoglobinuria is when vigorous exercise, such as prolonged marching or marathon running, can cause red cell damage and hemolysis in the capillaries of the feet.