One does not have to measure Vitamin D levels as a routine.
Measure the level only in situations like -
Symptoms and signs of muscle weakness
Evaluating Symptomatic cases of Hypocalcemia
Abnormal bone profile etc.
It should be noted that for routine screening for Vitamin D deficiency, 25 Hydroxy Vitamin D3 should be ordered in investigations and the other isomeric form of Vitamin D i.e. 1, 25 Di-Hydroxy Vitamin D, should not be used as a screening test for Vitamin D deficiency.