A 38 yo lady comes to you for a pre - employment physical exam. On
questioning you find out that she wakes up to pass urine 3 times in the night and also has
some degree of constipation. Physical exam is normal. She has no swelling of her feet and
feels fine.
You check her urine and find that the pH is 6.5, SG 1.008, Protein <40mg%, leukucyte-esterase - none, bilirubin none, glucose none, blood none. The serum including Na, K, HCO3, Cl, Urea and creatinin are normal.
She has no insurance and cannot pay for the full range of blood tests that you want to do. She asks you to pick out one or two tests only. Which ONE would you pick for her out of the following.