Question: A calcium figure of 11 mg / dL (normal less than 10.5 mg / dL) is found in a 30-year-old patient during a routine business examination. The PTH determination was 45 pg / ml (VN 10-55 pg / ml). The story is anodyne, except for the fact that the mother and the paternal grandfather were diagnosed with hyperparathyroidism and intervened, although they remained hypercalcemic. Which test is most useful to confirm the diagnosis? 
 Options:  <1> 25-OH D. <2> 1,25-OH 2D. <3> Calcium / creatinine ratio in urine. <4> Tubular reabsorption of phosphates. <5> PTHrP.
3