Vitamin D Testing Methodologies: Assessment Issues and Therapeutic Management

VITAMIN D TESTING METHODOLOGIES: ASSESSMENT ISSUES AND THERAPEUTIC MANAGEMENTJimmy L. Boyd, Asst. ProfessorMLT Program DirectorArkansas State University – Beebe

LEARNING OBJECTIVES

1) To provide an overview of the pathophysiology of Vitamin D metabolism

2) To differentiate the various available assay measures

3) To assess the serum/blood biomarkers associated with Vitamin D

4) To list various pros and cons to Vitamin D supplementation

REASONING & RATIONALE

A.Pandemic or Epidemic?

B. Prohormone or Vitamin?

C. Deficiency versus Insufficiency?

D. “Gold Standard” Laboratory method?

WHAT IS VITAMIN D?Fat soluble, steroidal pro-

hormone that is synthesized by the body as a precursor compound, which must be acted upon by UV-B rays (290 – 315 nm).

Regulation: Ca+2 and P-3

Metabolism: D2 , D3 , and DTotal

VITAMIN D – EPIDEMIOLOGY

No longer restricted to the disease: Rickets (Types)

Post-menopausal women on HRT

Elderly men and women (poor diets)

Problematic and extensive world-wide

Evolutionary/Historical Context

TYPES OF RICKETS

SYNTHESIS OF VITAMIN D

VITAMIN D RISK FACTORSLack of physical activity and adequate sun exposure,

Dark skin pigmentation

Excessive use of sunscreen lotions

Lack of Dietary intake/inappropriate supplementation

Obesity

Bariatric Surgery and associated Fat-malabsorption, including Celiac, Crohns, CF, and GERD, and Sprue

MEDICATION-RELATED RISK FACTORS

Vitamin-D Antagonists

Antieptileptic RxCorticosteroidsImmunosuppressantsHIV anti-retrovirals

Co-Morbid Illnesses

Renal Failure (ALL)Primary Hyper-PTHLiver Failure

BIOLOGICAL FUNCTIONS OF VITAMIN D

Bone Homeostasis

Bone Salts

Intestinal

Increased absorption

Kidneys

Inhibits loss of Ca+2

CANCER MECHANISMSMODALITY

A. Cell Cycle KineticsB. ImmunomodulatoryC. Oxidative StressD. InflammationE. HormonalF. Other

MECHANISTIC ROLES OF ACTION

Modulates cell proliferation, differentiation, and apoptosis; regulation of steroid receptor genes; growth factor signaling, cell adhesion, Angiogenesis, DNA report

Activity of NK cells and phagocytic fxn of macrophages; alpha-TNF in deficiency

Oxidative DNA damage, CRP levels with supplements; COX-2 enzymes with supplements, expression of Aromatase Estrogen Receptor

VITAMIN D RECEPTOR (VDR)

VDR is expressed in all major body tissues, e.g., Adipose, Brain, Intestines, Lymphocytes, MusclesAdrenalBoneBreastCartilageColonLiverLungKidneyParotid, Pituitary, Placenta, Testes, and Stomach

VDR MEDIATES VITAMIN D ACTIONS

1. Nuclear Hormone Receptor2. Located in numerous body sites3. Binds the active form of the hormone, leads

to the formation of a heterodimer with retinoid-X receptor – facilitates binding to VDRE

4. Decrease/Increase gene regulation 5. Modulate signal transduction pathways6. Differential effects based on the variations

in the VDR activity

RELATED DEFINITIONSVitamin D Deficiency – serum D (total) is < 20 ng/mL

Vitamin D Insufficiency – serum D (total) is 20 – 30 ng/mL

Vitamin D Sufficiency – serum D (total) is 30 – 100 ng/mL

Vitamin D Toxicity – serum D (total) is > 100 ng/mL

D(Total) = serum levels of 25-hydroxyvitamin D

RECOMMENDED IOM GUIDELINES

Infants, Children, Adolescents, and Adults: Ages < 51 years – 200 IU/day

Middle Age Adults: ages, 51 to 70 years – 400 IU/day

Elder Adulthood: > 70 years – 600 IU/day with Calcium supplement

(keep in mind the ½ life of Vit. D – 14 to 20 days)

LABORATORY TESTING METHODOLOGIES

Increased Testing Volumes

2006 – 19,000 2008 – 61,000 2010 – 120,0002012 – 160,000

Random Reference Ranges

D2 – Ergocalciferol, D3 – CholecalciferolD (total) – Calcitriol (25-OH Vitamin-D)

Analytical ChallengesLC/MS ImmunoAssay Chemiluminescence

RELATED ANALYTICAL STUDIESRandomized Controlled Trials:

Biscoff-Ferrari, Willett, Wong, et. al., 2005 (JAMA)

DEQASNISTSRMJCTLMSteerman & Svec (2009) Military MedicineOrelind, Feinglass, et al., (2012) South. Med. J.Zee, Fudge, Whiting, et al., (2012) Assn. Clin. Bioch.Carter, G. (2011) Accuracy of 25-OH Vit. D., Current Drug Targets

RECOMMENDATIONS & CONCLUSIONS

More physician-informed assay actions

Re-assessment of insidious disease processes

Balance of Safety, Efficacy, and Toxicity

Need for International Standardization

CONCLUSIONSQuestions????

Answers!!!

Thanks for your time…