Objective and Hypotheses. The objective of this study is to evaluate the urine calcium-to-creatinine ratio as a noninvasive and inexpensive screening test for vitamin D deficiency. Our hypotheses are 1) that the urine calcium-to-creatinine ratio correlates with blood vitamin D levels in infants and toddlers at risk for vitamin D deficiency and 2) that this test can be used to screen for vitamin D deficiency.