Week 5 Interpretation of Common Labs: Water and Fat Soluble Vitamins

Question 1

Lab Assessment of folate status

Answer 1

• Serum Folate reflects shorter term (2-3 weeks): >3.5 nmol/L
• Erythrocyte Folate - reflects longer term status (weeks to months): >216 nmol/L
• Plasma Homocysteine

Question 2

Lab assessment of B12

Answer 2

• Monitoring: Serum levels of B-12 q 1-2 months re: efficacy of supplementation/timing of supplementation: 150-670 pmol/L
• Schillings Test
• Methylmalonic acid (deficiency > 1000mmol/L)
• Plasma Homocysteine concentrations
• CBC: macrocytic anemia: not specific only to B- 12 status

cobalamine

Question 3

Lab assessment of thiamin

Answer 3

Erythrocyte transketolase activity (90-160 μg
sedoheptulose formed/mL/hr): TDP 0-15%

B1

Question 4

lab assessment of riboflavin

Answer 4

typically more research
* HPLC analysis of FMN
* Urinary excretion (per μg or μg /g of creatinine)
* Erythrocyte < 27 μmol/dL=deficient status

Question 5

Assessment of Vitamin A status

Answer 5

Vitamin A: 0.7-2.1 μmol/L
* Plasma retinol concentrations good biochemical measure of vitamin A status → levels reflect status best if the individual has exhausted stores
* Assessment for Bitot spots in eyes
* Variables influencing serum vitamin A levels: prior intake of vitamin A (supplementation)

Question 6

Vitamin A Interactions with Other utrients

Answer 6

• Cleavage of b-carotene into retinal requires sufficient vitamin E
• Protein status:directly affects RBP (retinol binding protein) synthesis
• Zinc deficiency: ↓ [plasma retinol], ↑ [liver retinol] and ↓ liver mobilization of stores (inhibits release of retinyl ester hydrolase resulting in limited access to vitamin A stores)

Question 7

Assessment of vitamin D status

Answer 7

Plasma levels of 25-OH Vitamin D
* Winter 20-60 nmol/L (suboptimal)
* Summer 25-80 nmol/L
* Consider values > 80 nmol/L to determine adequacy of status (lots of controversy about cut-off for overall health status)
* Consider calcium and phosphorus status

Question 8

Active Form of Vitamin D

Answer 8

1,25-OH Vitamin D
* Liver: 25 hydroxylation of cholcalciferol
(NADPH-dependent enzyme)
Kidney: 1 hydroxylation of cholcalciferol

Question 9

Major storage sites of vitamin D

Answer 9

• skin
• muscle
• adipose tissue

Question 10

Important Regulators of vitamin D Status

Answer 10

• Parathryoid hormone (PTH)
• Serum concentrations of calcium & phosphate

Question 11

Assessment of vitamin E status

Answer 11

• Serum vitamin E levels: 12-46 μmol/L
• Consider the ratio of serum vitamin E:total serum lipid concentrations
• Children: ratio of <0.8 mg/g indicative of deficiency

Question 12

Major Forms of Vitamin K

Answer 12

• Phylloquinone-major form in blood
• Menaquinone-major storage form (biological
  role unknow)

Question 13

Vitamin K interactions

Answer 13

• Excessive vitamin A can interfere with vitamin K absorption
• Vitamin E may enhance K absorption

Question 14

Vitamin K major storage site

Answer 14

liver (approx 24 hour supply)

Question 15

Assessment of vitamin K status

Answer 15

• Delayed PTT or ↑ INR: poor marker as can still have normal levels even if depleted. Use most often clinical setting
• Serum levels of phylloquinone: half life < 8 hours so not a good marker of total body status (more reflective of recent dietary intake).