PTFQI

PTFQI (Parametric Thyroid Feedback Quantile-based Index for FT4) estimates pituitary TSH sensitivity to Free T4 while remaining stable at extreme hormone values. Values range from -1 to +1, zero means TSH is exactly what's expected for the given FT4. Low PTFQI means TSH is lower than expected for the given FT4 (apparent pituitary over-sensitivity or impaired TSH secretion; very low values may support central hypothyroidism). High PTFQI means TSH is higher than expected for the given FT4, most commonly seen in subclinical hypothyroidism.