Development of a non-invasive clinical screening tool to asses 25-hydroxyvitamin D (25(OH)D) serum levels in long-term care older adults

Robbins, Ronna Nikole Osborn
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The purpose of this study was to develop, test, and enhance a non-invasive clinical diagnostic screening tool for the identification of hypovitaminosis D, 25-hydroxyvitamin D [25(OH)D] serum levels <30 ng/mL, in older adults living in long-term care communities. The primary hypothesis of this study was that hypovitaminosis D could accurately be predicted in long-term care older adults through a series of healthrelated and demographic characteristics. This observational cross-sectional study recruited older adults >65 years from five long-term care communities in central Texas. A one-time venous blood draw measuring 25(OH)D serum level was obtained from each participant. Several multiple logistic regression models were tested to identify the best fitting model that described the relationship between categorical insufficient (<30 ng/mL) 25(OH)D serum levels and health-related conditions, demographics, and clinical characteristics. Inter-rater reliability was established using the test-retest method. The developed screening tool was administered to a randomized subset of participants (n=50), each of whom had the screener administered twice by blinded trained data collectors, resulting in two screeners per participant (n=100 screeners). Of the 180 participants recruited, 173 provided blood samples and had complete data sets. The mean age was 83.0 (+ 11) years, 107 (61.2%) were female, 159 (89%) were Caucasian, 65 (38%) were not prescribed a vitamin D supplement, and 94 (54%) participants had hypovitaminosis D (<30 ng/mL). Mean vitamin D supplementation rate was 1190 IU/d with mean 25(OH)D serum levels of 32.5 ng/mL. There were no significant differences between demographic characteristics (gender, age, BMI, etc.) in 25(OH)D serum levels and dose rate of vitamin D supplementation. Using only ten clinical variables, the screening tool significantly predicted hypovitaminosis D “insufficient” serum levels (p<0.001) and accounted for approximately 30.6% of the variance in 25(OH)D serum levels. The screening tool accurately predicted serum levels 74.16% of the time, with 53.85% of adequate (>30 ng/mL) serum levels correctly classified (specificity) and 90.00% of hypovitaminosis D correctly classified (sensitivity). Inter-reliability testing indicated that there was significant agreement between the two administered screeners (p<0.000). This study successfully developed a low cost, easy to administer, non-invasive diagnostic clinical screening tool that can identify hypovitaminosis D, 25(OH)D serum levels <30 ng/mL, in older adults living in long-term care communities.