Accuracy-Based Vitamin D Survey: Six Years of Quality Improvement Guided by Proficiency Testing

Context.— The goal of the College of American Pathologists Accuracy-Based Proficiency Testing Program is to promote the quality, standardization, and harmonization of clinical laboratory results through proficiency testing specimens that are free from matrix effects, have target values that are traceable to reference methods, and that probe the limitations of current methods. Objective.— To summarize the first 6 years of the Accuracy-Based...