VITAMIN/MINERAL


Niacin (B3) N1


N1 -methylnicotinamide -methyl-2-pyridone-5-carboxamide (2-pyridone)


Pyridoxine (B6) Pyridoxal 5’-phosphate (PLP)


4-Pyridoxic acid (PA)


Erythrocyte aspartate aminotransferase (eAST) index & Erythrocyte alanine aminotransferase (eALT) index


Folate (B9) Folate


Plasma or RBC


24-hour urine Whole blood


39-98 nmol/L


> 3 μmol/d <1.6 <1.25


RBC erythrocyte Serum or plasma


Cobalamin (B12) Vitamin B12


Methylmalonic acid (MMA) Homocysteine (Hcy)


Serum or plasma Serum


Serum or plasma 170-250 pg/mL


0.08-0.56 μmol/L


5-15 μmol/L 65 y: <20 μmol/L


Adult: 140-628 ng/mL Pediatric: >160 ng/mL


<20 nmol/L <3 μmol/d


PLP indicates recent intake; need to fast 8-12 hours for more accurate level.


If low albumin, altered alkaline phosphatase, or critically ill intestinal transplant patient, RBC PLP more reliable than plasma PLP.


A combination of the 3 tests is recommended. Diagnosis of toxicity is clinical.


<140 ng/mL <3 ng/mL


<150 pg/mL Elevated


Elevated


Some sources suggest <300-350 pg/mL indicates deficiency.


Megaloblastic anemia = mean corpuscular volume (MCV) >100 fL/cell; even if no ane- mia, folate can mask vitamin B12 deficiency.


MMA and hcy greater than normal support vitamin B12 deficiency.


Note: Hcy may increase in folate deficiency; MMA may increase with renal failure or intravascular volume depletion.


LABORATORY ASSAYS FOR VITAMIN AND MINERAL STATUS PEDIATRIC MALNUTRITION INDICATORS 58


Plasma homocysteine level of ≥15 μmol/L can indicate folate and/or vitamin B12 deficiency.


Normal methylmalonic acid level in folate deficiency


LABORATORY METHOD NORMAL


24-hour urine 24-hour urine


17.5-46.7 μmol/day


INTERPRETATION DEFICIENCY TOXICITY


<5.8 μmol/day <2 mg/g Cr


Diagnosis of deficiency is usually clinical.


COMMENTS


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