TABLE 6.
Commonly used cutoffs for nutritional biomarkers measured in NHANES1
| Nutritional biomarker and matrix | Cutoff (reference) | Unit | Age or population | Interpretation | Comment |
| Folate, total | |||||
| Serum | <7 (26) | nmol/L | All ages | Risk of megaloblastic anemia | Assay used for cutoff was traditional microbiological assay |
| RBC | <305 (26) | nmol/L | |||
| Serum | <10 (68) | nmol/L | All ages | Possible deficiency based on elevated metabolic marker tHcy | Assay used for cutoff was BioRad radioassay |
| RBC | <340 (68) | nmol/L | |||
| RBC | <906 (35) | nmol/L | WRA | Insufficiency based on elevated neural tube defect risk | Assay used for cutoff was updated microbiological assay using folic acid calibrator |
| PLP | |||||
| Serum | <20 (26) | nmol/L | All ages | Low status; basis for Estimated Average Requirement | Cutoff may overestimate vitamin B-6 requirement for health maintenance of more than half the group |
| Vitamin B-12 | |||||
| Serum | <74 (69) | pmol/L | All ages | Deficient | Suggested criteria based on combination of vitamin B-12 with metabolic markers MMA and tHcy (70) |
| <148 (26) | pmol/L | All ages | Moderately low | “Clinical” deficiency: vitamin B-12 low (<148 pmol/L), often very low (<74 pmol/L) and metabolic abnormalities present, often severe (MMA >1000 nmol/L, tHcy >50 μmol/L) | |
| 148–222 (26) | pmol/L | All ages | Low normal | “Subclinical” deficiency: vitamin B-12 low (<148 pmol/L) or low normal (185–258 pmol/L) and ≥1 metabolic abnormality present, usually mild (MMA 300–800 nmol/L, tHcy 15–25 μmol/L) | |
| tHcy | |||||
| Plasma | >12–14 (26) | μmol/L | All ages | Low folate, vitamin B-2, vitamin B-6, or vitamin B-12 status | May need separate cutoffs by age or sex; impaired renal function is a confounder (increased tHcy) |
| MMA | |||||
| Plasma | >271 (26, 71) or >376 (71) | nmol/L | All ages | Low vitamin B-12 status | Statistically derived (2 or 3 SDs); may need separate cutoffs by age; impaired renal function is a confounder (increased MMA) |
| Vitamin C | |||||
| Serum | <11.4 (72) | μmol/L | All ages | Clinical deficiency | Risk of scurvy |
| 11.4–23 (72) | μmol/L | All ages | Low status | ||
| Vitamin A | |||||
| Serum | <0.70 (27) | μmol/L | All ages | Risk of deficiency in population | Prevalence of low serum retinol to define public health problem: 2–9% (mild), 10–19% (moderate), ≥20% (severe) (73); inflammation is a confounder (decreased serum retinol) |
| Vitamin E | |||||
| Serum | <14 (72) | μmol/L | All ages | Risk of deficiency | |
| 25(OH)D | |||||
| Serum | <30 (74) | nmol/L | All ages | Risk of deficiency | Cutoffs developed by using radioassay are in use with HPLC-tandem MS and other methods; new cutoffs may need to be developed |
| 30 to <50 (74) | nmol/L | All ages | Risk of insufficiency | ||
| <40 (74) | nmol/L | All ages | Risk of inadequate intake | ||
| >125 (74) | nmol/L | All ages | Risk of excess | ||
| Ferritin | |||||
| Serum | <12 (75) | μg/L | 1–5 y | Depleted iron stores | Inflammation is a confounder (increased serum ferritin) |
| <15 (75) | μg/L | >5 y | |||
| >150 (75) | μg/L | Women | Risk of iron overload | Other indicators should be included in clinical evaluation | |
| >200 (75) | μg/L | Men | |||
| sTfR | |||||
| Serum | >6.0 (76) | mg/L | 1–5 y | Functional iron deficiency | Statistically derived (97.5th percentile) from NHANES 2003–2010; assay-specific cutoffs |
| >5.33 (76) | mg/L | WRA2 |
1
MMA, methylmalonic acid; PLP, pyridoxal-5′-phosphate; sTfR, soluble transferrin receptor; tHcy, total homocysteine; WRA, women of reproductive age (12–49 y); 25(OH)D, 25-hydroxyvitamin D.
2
Nonpregnant women.