In reduced eGFR only (<90 mL/min × 1.73 m2), low urine Ca/Cr independently related to low serum 1,25-dihydroxyvitamin D (p = 0.002) and did not relate to hyperphosphatemia, high serum parathyroid hormone, or hypocalcemia (p ≥ 0.14). The gene discussed is PTH; the disease is hyperphosphatemia.