Heme Q?

[LotaPower]

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Anyone know the significance of measuring methylmalonic acid/homocystine levels when investigating a macrocytic anemia (i.e. B12/folate def)? when and why dod you get it and what do they mean??

Sorry to post this on sdn, but i think i had an absence seizure when my attending was explaining this. 😴 😕

 

[LotaPower]

Anyone know the significance of measuring methylmalonic acid/homocystine levels when investigating a macrocytic anemia (i.e. B12/folate def)? when and why dod you get it and what do they mean??

Sorry to post this on sdn, but i think i had an absence seizure when my attending was explaining this. 😴 😕

come on folks, im sure the medicine shelf is coming up for some of you...help a brotha out!

 

[Janders]

come on folks, im sure the medicine shelf is coming up for some of you...help a brotha out!

So one thing folic acid does is help to convert homocystine to... something. So if your folic acid levels are low, your homocystine levels are high. Homocystine is believed to make atherosclerosis worse, so it has some cx relavence. I believe you just treat with Folic Acid.

(Just looked it up, Homocystine is converted to Methionine.)

Take that with a big coming-from-an-MS2 grain of salt,

 

[smgilles]

Anyone know the significance of measuring methylmalonic acid/homocystine levels when investigating a macrocytic anemia (i.e. B12/folate def)? when and why dod you get it and what do they mean??

Sorry to post this on sdn, but i think i had an absence seizure when my attending was explaining this. 😴 😕

You need both B12 and Folate to convert methionine to homocysteine (using MethylTHF-homocysteine Methyl Transferase) and a deficiency of either will lead to a megaloblastic anemia. You also need B12 to convert methylmalonyl CoA to Succinyl CoA, but this reaction does not require Folate. So one way to differentiate b/w Folate or B12 is by looking for Methylmalonic aciduria.

 

[Spiff]

Anyone know the significance of measuring methylmalonic acid/homocystine levels when investigating a macrocytic anemia (i.e. B12/folate def)? when and why dod you get it and what do they mean??

As I understand it, in a nutshell, serum B12 levels don't always correspond with tissue B12 levels and overt clinical pernicious anemia is preceeded by a long period of metabolic B12 deficiency. So the idea is you want to screen for deficiency in the preclinical stage before you get all of the neuropsychiatric and hematologic symptoms. Additionally a couple of studies have suggested that preclinical B12 deficiency may result in increased cardiovascular risk due to elevated homocysteine levels.

So you can measure serum or urine MMA levels in "at risk" populations (geriatric, Crohns/malabsorption, cirrhosis et.c) and detect impending clincial B12 deficiency. You can also check MMA levels if the B12 is still in the "normal" range, but maybe borderline for your patient. The usual cut-off is about 400. So if you have a hardcore vegan with a B12 level < 400 (still technically "normal", MMA might be a good test to rule out metabolic B12 deficiency. In the geriatrics clinic they got an MMA level on everyone over 65 who had not previously been screened.

Anyway, hope that makes sense. Also, for "pimpage" purposes the big false positive for urine MMA is renal failure, where MMA will be elevated independently of tissue B12 levels.

 

[DarksideAllstar]

Something that I picked up as well...
If you think that someone is deficient in folate order an RBC FOLATE. The serum folate fluctuates on a day-to-day basis with diet.
Also, the MCV doesnt have to be elevated in B12 or folate deficiency.