FGF21 and Huntington disease: In HD patients with 24-hour urine volume ≤ 100ml, the AUC of FGF21 combined with age in predicting osteoporosis was 0.833 (95 % CI, 0.772 to 0.894, P < 0.001) with good sensitivity (61.8 %) and specificity (90.5 %).