Cystathionine; homocysteine; 2-methylcitric acid; methylmalonic acid
5 - 7 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Serum or plasma
Red-top tube, gel-barrier tube, or green-top (heparin) tube
Separate serum or plasma from cells within one hour of collection and transfer to a plastic transport tube.
Specimen received not separated from cells; plasma from a blue-top or yellow-top tube; citrate interferes with assay; homocysteine results increase by approximately 35% and 75% for specimens not centrifuged and/or not separated from the clot for periods of four and 24 hours respectively
Diagnose megaloblastic anemia. Elevated levels of methylmalonic acid provide an early indication of cobalamin (B12) deficiency.
Liquid chromatography/tandem mass spectrometry (LC/MS-MS)
Serum methylmalonic acid and homocysteine are the primary metabolic tests for diagnosing and distinguishing between B12 and folate deficiency. They can be used in conjunction with the serum B12, which is usually low or low normal (<350 pg/mL) in B12 deficiency, and the serum folate, which is usually low or low normal (<5 ng/mL) in folate deficiency. 2-Methylcitric acid and cystathionine provide confirmatory evidence for such deficiencies. Homocysteine, and especially cystathionine, may also be high in B6 deficiency.
Elevated levels of serum metabolites will correct to normal after treatment with the appropriate vitamin but will not correct after treatment with the wrong vitamin, even in pharmacologic amounts.
Any of the four metabolites can be elevated due to renal insufficiency or intravascular volume depletion. This occurs most commonly in the case of 2-methylcitric acid and cystathionine. Elevated metabolite levels do not correct with B12, folate, or B6 treatment, unless vitamin deficiency coexists.
Normal ranges six hours postoral methionine load (100 mg L-methionine/kg body weight) are as follows: homocysteine: 16.5−45.7 μmol/L and cystathionine: 424−2500 nmol/L. Methylmalonic acid and 2-methylcitric acid do not change after a methionine load.
The megaloblastic anemia profile monitors four compounds: methylmalonic acid, 2-methylcitric acid, homocysteine, and cystathionine. It has been shown that all four of these compounds are elevated if a patient is suffering from vitamin B12 deficiency (megaloblastic anemia, cobalamin deficiency) and that homocysteine and cystathionine are elevated if there is a folic acid deficiency. Methylmalonic acid and homocysteine are the primary tests for diagnosis. 2-Methylcitric acid and cystathionine provide confirmatory information.
This method is a more specific diagnostic tool for B12 and folate deficiencies as it has been shown that some patients with deficiencies will have normal or borderline serum B12 or folate. A deficiency of vitamin B12 can lead to incapacitating and life-threatening neuropsychiatric abnormalities, which are completely reversible by treatment with B12. As with any such condition early detection is very important. This profile provides early detection and differentiation. This differentiation is very important because both B12 and folate deficiencies have indistinguishable hematological abnormalities. The greatest improvement is observed when the proper vitamin is used and only B12 will correct the neuropsychiatric abnormalities seen in cobalamin deficiency.
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|706960||Anemia, Megaloblastic, Serum||706797||Methylmalonic Acid, Serum||nmol/L||13964-2|
|706960||Anemia, Megaloblastic, Serum||706962||2-Methylcitric Acid, Serum||nmol/L||26904-3|
|706960||Anemia, Megaloblastic, Serum||706963||Homocysteine, Serum||umol/L||13965-9|
|706960||Anemia, Megaloblastic, Serum||706967||Cystathionine, Serum||nmol/L||26607-2|
|706960||Anemia, Megaloblastic, Serum||706969||Continued:||N/A|
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