Diagnosis of vitamin D deficiency, hypervitaminosis D, differential diagnosis of causes of rickets and osteomalacia, monitoring vitamin D replacement therapy 25-Hydroxy (Vitamin D3) test is done as a routine work-up to assess the sufficiency of Vitamin D, Insufficient vitamin D levels lead to thin, brittle bones. Vitamin D sufficiency prevents rickets in children and osteomalacia in adults. Together with calcium, vitamin D also helps protect older adults from osteoporosis. It is also produced endogenously when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis. Vitamin D obtained from sun exposure, food, and supplements Few food are the natural source of Vitamin D like flesh of fatty fish (such as salmon, tuna, and mackerel) and fish liver oils, Small amounts of vitamin D are found in beef liver, cheese, and egg yolks