15 Feb How can you differentiate between vitamin B12 deficiency and folate deficiency?

Both of these deficiencies present with macrocytic anemia and they often co-exist.

In both of these conditions, the level of homocysteine in the blood goes up, but only in vitamin B 12 deficiency methylmalonic acid level in serum goes up.

The reason for this is both vitamin B 12 as well as folic acid are involved in the conversion of homocysteine to methionine. Therefore, if there is a deficiency of either one of them, there will be an increase in the level of homocysteine. That is the reason why homocysteine level alone cannot help to distinguish between vitamin B12 or folate deficiency.

When this reaction is taking place, vitamin B 12 simultaneously helps another reaction to carry forward, that is the conversion of Methlymalonyl CoA into Succinyl-CoA. Methylmalonyl CoA in this reaction comes from Methylmalonic acid. So if there is vitamin B12 deficiency, then the level of methylmalonyl CoA goes up, which subsequently increases the level of methylmalonic acid.

As this conversion is taking place only with the help of vitamin B12, in the deficiency of vitamin B12, there will be an increase in homocysteine as well as an increase in methylmalonic acid, whereas in the case of folate deficiency there will only be an increase in homocysteine.