I was tested three months ago at my doctor's office and the results came back at 58 ng/ml. I had been taking (and continue to take) 5000 IUs a day. My diet, sun exposure and health haven't changed but the results from the home Vitamin D kit came back at 34.6 ng/ml. What would cause this large difference? I was really surprised – especially since the increase to 5000 IUs had changed my earlier levels from 37 to 58.