Vitamin D deficiency test for the elderly

Patient: My 80 year old mother lives alone, and rarely gets out, she has complained about dizzy turns just lately and has had one fall. She sees her G.P and Cardiologist fairly frequently and has no heart problems.I suggested to her that perhaps she is suffering from vitamin D deficiency and that is it a fairly simple test to find out if that is the case, and very easy to remedy if it turns out she is indeed deficient.She recently had a series of routine blood tests to measure her cholesterol levels and also calcium, sodium potassium, creatinine, liver function test etc. I asked my mother to ask the GP for a vitamin D and B6 and B12 measurement at that time. When the results came back the GP said that the numbers were “fine” When asked for the actual levels of vitamin D, and if in fact they had been measured, the GP got a little flustered and replied that everything was fine and that the vitamin levels are expressed in the other blood fractions mentioned above.My question is, is what the GP said true? Does a routine and somewhat limited standard blood test for cholesterol levels accurately determine vitamin D levels? Or does a measurement of vitamin D deficiency require a specific test? I have read on the webthat a 25-hydroxyvitamin D, or 25(OH)D, test is required to specifically determine if there is vitamin D deficiency.thank you in advance for any replies on this topic.Chris