Specimen

Serum More information

Collection Medium:

Alternate
Collection Media:

Light Green top tube (Lithium Heparin)

Minimum:

1.0 ml serum or 2.5 ml whole blood from plain red top tube (no 
additive)

Delivery Instructions:

Deliver to laboratory within 30 minutes of collection.

Specimen
Instructions:

Laboratory must process specimen within one hour of collection or 
specimen must be kept on ice.

Analytic Time:

1 week

Reference Range:

                    NORMAL     B12 DEFICIENCY     FOLATE DEFICIENCY
Metabolite          %HIGH          %HIGH                %HIGH
                 RANGE VALUES   RANGE VALUES         RANGE VALUES

Methylmalonic Acid:
                 73-271    <3   271-200,000 >95      73-271    <3
2-Methylcitric Acid:
                 60-228    <3   228-15,000  >80      60-228    <3
Homocysteine:
                5.1-13.9   <3    14-500     >95      14-250    >95
Cystathionine:
                 44-342    <3   342-4000    >80     342-18,000 >80

Test
Limitations:

NOTE 1)Serum Methylmalonic Acid and Homocysteine are the primary 
metabolic tests for diagnosing and distingushing 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.

NOTE 2) 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.

NOTE 3) 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.

NOTE 4) Serum metabolite levels can be rechecked 5 to 15 days after 
vitamin therapy.

NOTE 5) Normal ranges 6 hours post oral Methionine load (100 mg 
L-Methionine/kg body wt.) are as follows: Homocysteine 16.5-45.7 
umoles/Liter and Cystathionine 424-2500 nmoles/Liter. Methylmalonic 
Acid and 2-Methylcitric Acid do not change after a Methionine load.

Methodology:

Gas Chromatography-Mass Spectrometry (GC-MS)

CPT Code:

82136 Homocysteine and Cystathionine
83918 Methylmalonic Acid and Methylcitric Acid

See also:
Folate, Serum
Homocysteine, Plasma
Methylmalonic Acid, Serum
Vitamin B12, Plasma

See Additional Information:
Specimens Requiring Immediate Delivery