Financial service providers market many different products as being available for nominal fees. A nominal fee is a payment or purchase price like any other fee. However, the use of the work nominal implies that the fee is small in comparison to the true value of what you can purchase with it.
Creatinine clearance in a healthy young person is about 125 milliliters per minute -- meaning each minute, that person's kidneys clear 125 mL of blood free of creatinine. The GFR can vary depending on age, sex, and size. Generally, the creatinine clearance is a good estimation of the glomerular filtration rate.
No, the .gfr test is for kidney function. I just recently got my Vit D results as well and it is 17 and I was told it should be 30 to 50. I have RA and we usually have low Vit D. So your disorder/disease may cause low levels. That is a good question for your doc. They put me on 50,000 ut Vit D once a wk.