Serum triiodothyronine-to-thyroxine (T3/T4) ratio predicts therapeutic outcome to biological therapies in elderly IBD patients.

Introduction: Rates of elderly patients with inflammatory bowel diseases (IBDs) are increasing, and biomarkers are needed to optimise their therapies. Serum triiodothyronine-to-thyroxine (T3/T4) ratio has been correlated with geriatric patient frailty.

Aim: To assess the suitability of T3/T4 ratio as a response marker to biologics in elderly patients with IBD.

Methods: Patients with IBD over 60 years old were enrolled, when starting biological therapy. Therapeutic outcome was assessed after 54 weeks of treatment as mucosal healing (Mayo endoscopic score < 2 for ulcerative colitis; ulcer disappearance for Crohn's disease) and clinical remission (Partial Mayo Score < 2 for ulcerative colitis; Harvey-Bradshaw Index < 5 for Crohn's disease). T3/T4 ratio was evaluated at baseline, and its association with therapeutic outcomes was tested by multivariable logistic regression and receiver operating characteristic (ROC).

Results: We enrolled 80 patients; 44 achieved clinical remission and 36 mucosal healing. Baseline T3/T4 ratio was higher in patients with mucosal healing, as compared with those without mucosal healing (P < 0.0001), regardless of the disease type or biological drug (OR 6.4 [2.9-14.3] for each T3/T4 unit increase, P < 0.0001). A cut point of 3.3 was identified as the optimal threshold of baseline T3/T4 ratio for predicting mucosal healing, providing 78% sensitivity and 89% specificity (area under the ROC curve 0.88 [0.79-0.94]; positive and negative likelihood ratios 6.8 [2.9-15.9] and 0.3 [0.1-0.5] respectively).

Conclusions: T3/T4 ratio seems a reliable tool for predicting therapeutic outcome of biological therapy in elderly patients with IBD. If validated, the assessment of this parameter before starting biological treatment might be suggested.