Although folate is present in nearly all foods, it is destroyed by 10 to 15 minutes of cooking, and as a result folate stores are marginal in a surprising number of healthy persons.

Vitamin B12 is widely present in foods, is resistant to cooking and boiling, and is even synthesized by gut flora.
Thus, unlike folate, vitamin B12 deficiency is virtually never caused by inadequate intake except in vegetarians who scrupulously avoid milk and eggs. Instead, deficiencies typically arise from some abnormality that interferes with vitamin B12 absorption.

Non-megaloblastic, macrocytic anemia (MCV>100 fL)

Caused by alcoholism, hyperlipidemia, hypothyroidism, and liver disease.

The red cell membrane is composed of a lipid bilayer that will freely exchange with the plasma pool of lipid. Conditions such as liver disease, hypothyroidism, hyperlipidemia and pregnancy are associated with raised lipids and may cause a raised MCV, but is usually less than 110 fL (unlike in megaloblastic anemia, which causes MCV >110 fL)

Why Iron deficiency causes microcytosis (cells smaller than normal)?
This is because the maturing red cells undergo an extra cellular division before the critical haemoglobin concentration required to arrest mitosis is achieved. The cells are also hypochromic, with a larger area of central pallor

كريات الدم الحمر تحتاج حد أدنى من الهيموغلوبين حتى تتوقف عن الإنقسام. لما تركيز الهيموغلوبين يكون قليل (بسبب نقص الحديد)، الكريات رح تنقسم لخلايا أصغر لحدما توصل لتركيز الهيموغلوبين المطلوب، لهذا نقص الحديد رح يسبّب microcytosis.

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.

Gestalt impression ha

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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.