title: Assessment of low vitamin D among Saudi Arabians. Did we overshoot the runway?
abstract: OBJECTIVE
  To compare the performance of 3 commonly used 25-hydroxyvitamin D (25-OHD) assays among a sample of the Saudi population.
  
  
  METHODS
  This cross-sectional study was carried out between January 2011 and December 2012 at King Fahd Hospital of the University, Al-Khobar, Saudi Arabia. After informed consent, blood samples for measurement of 25-OHD level was extracted from 200 adults. The vitamin D levels of each individual were determined using chemiluminescence immunoassay (CLIA), radio-immuno assay (RIA), and liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay. Assays were also compared through commonly used cut-points for classification of vitamin D deficiency. Bias between assays was evaluated using Bland-Altman plots.
  
  
  RESULTS
  The average age of patients was 45.7+/-16.1 years. A significant difference between the assays was found. The mean 25-OHD levels were highest for the LC-MS/MS (21.65 ng/mL, 95% CI 19.74-23.56), intermediate for RIA (16.607 ng/mL, 95% CI 14.87-18.32), and lowest for CLIA method (13.864 ng/mL, 95% CI 12.109-15.618). Using 30 ng/mL as a cutoff value, only 6% was found to have normal levels of 25-OHD using CLIA, 9% using RIA, and 22% using LC-MS/MS.
  
  
  CONCLUSIONS
  Levels of 25-OHD and the prevalence of vitamin D deficiency are dependent on the assay used. The reported high prevalence of hypovitaminosis D among the Saudi population can be partially explained by the use of assays that underestimate vitamin D levels.
authors.affiliation: Department of Orthopedic Surgery, College of Medicine, King Fahd Hospital of the University, University of Dammam, Dammam, Kingdom of Saudi Arabia. E-mail. drsadat@hotmail.com.
authors.forename: Mir
authors.initials: M
authors.lastname: Sadat-Ali
authors.forename: Abdulmohsen H
authors.initials: AH
authors.lastname: Al-Elq
authors.forename: Iman H
authors.initials: IH
authors.lastname: Al-Shaikh
authors.forename: Haifa A
authors.initials: HA
authors.lastname: Al-Turki
authors.forename: Amein K
authors.initials: AK
authors.lastname: Al-Ali
authors.forename: Abdallah A
authors.initials: AA
authors.lastname: Al-Othman
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002853:Chromatography, Liquid; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008163:Luminescent Measurements; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011863:Radioimmunoassay; D012016:Reference Values; D012529:Saudi Arabia / Q000453:epidemiology; D053719:Tandem Mass Spectrometry; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology; D055815:Young Adult
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D