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…