There is no gold standard assay to confirm a<unk> . Serum levels of<unk>  are often low in<unk> , but if there are clinical signs that conflict with normal levels of<unk> <unk> ; additional investigations are justified. Diagnosis is often suspected first, as diagnosis usually requires several tests, these include: * Complete blood count; a routine complete blood count shows anemia with an elevated mean cell volume * Serum<unk> <unk> ; a level below normal indicates a deficiency * Methylmalonic acid and/or homocysteine; If the serum<unk> <unk>  is at the normal level, methylmalonic acid and/or homocysteine assay is required. higher levels indicate a deficency, indicators are usually more reliable * Intrinsic factor and parietal cell antibodies; The blood is tested for antibodies against intrinsic factor and the parietal cells of the stomach In some cases, a peripheral blood smear may be used; which may allow to show macrocytes and hypersegmented polymorphonuclear leukocytes. If nervous system damage is present and blood testing is inconclusive, a lumbar puncture to measure cerebrospinal fluid B-12 levels may be done. On bone marrow aspiration or biopsy, megaloblasts are seen. The Schilling test was a radio-isotope method, now outdated, of testing for low<unk> <unk> . Serum levels A blood test will provide the levels of<unk> ,<unk>  can be determined by serum. In recent years,<unk> <unk>  serum has been considered somewhat unreliable, as deficiency may be present within the normal serum levels. When clinical symptoms conflict with the serum normal levels, other tests may be required. The normal serum levels are considered to be between (200–980 pg/mL). A levels less than 350 pg/mL are considered a borderline deficiency; and a levels less than 200 pg/mL are considered a deficiency; while a levels below 170 pg/mL are considered severe. Some researchers have suggested that current standards for<unk> <unk>  levels are too low. a japanese study showed that the normal limits should be between (500-1300 pg/ml).
Vitamin B12 deficiency
Vitamin A deficiency
Copper deficiency
Biotin deficiency
Megavitamin-B6 syndrome
Vitamin E deficiency
Fluorine deficiency
Zinc deficiency