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Vitamin D tests had poor agreement – yet again – April 2011

Vitamin D Status of Adults from Tropical Australia Determined Using Two Different Laboratory Assays: Implications for Public Health Messages

Madeleine Nowak1,*, Simone L Harrison1, Petra G Buettner1, Michael Kimlin1,2, David Porter1,3, Lee Kennedy4, Rick Speare1 DOI: 10.1111/j.1751-1097.2011.00941.x
Photochemistry and Photobiology

We measured serum 25 hydroxyvitamin D 25(OH)D levels of ambulatory adults in tropical Australia to determine whether it is appropriate to continue promoting sun-safety in this population. In August 2006 (winter), self-administered questionnaires were completed by 145 Meals-on-Wheels volunteers (49.3% male; mean age 57.8±14.7 years; 76.6% response) from Townsville, Queensland (Latitude 19oS). Serum 25(OH)D was analysed using two common assays.

Mean levels were 68.3 (SD±18.7; range 26-142) by DiaSorin Radioimmunoassay and 83.0 (SD±30.8; range 30-184) by DiaSorin Liaison® one. No participants were 25(OH)D deficient (<25nmol/l). Nine participants (6.2%) had 25(OH)D levels between 25 and 50 nmol/l (insufficient), by both methods (seven with a BMI?25). Twenty eight participants (19.3%) had one result in the insufficient range and the other in the adequate range. Thus, almost all of these free-living adults in tropical Australia had adequate vitamin D levels at the end of winter.

There was poor agreement between the two 25(OH)D assays . These results suggest it is appropriate to continue promoting sun-safe messages to the ambulatory Caucasian adult population of North Queensland, which has an extremely high incidence of skin cancer.

The lack of agreement between the two assays is a concern. Few doctors are aware of this measurement issue.
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See also VitaminDWiki

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