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Biomarkers

PTFQI — Parametric Thyroid Feedback Quantile-based Index

Rank-based sensitivity of the pituitary to free T4

The set point of TSH and free T4 on the population distribution curves

PTFQI (Parametric Thyroid Feedback Quantile-based Index) is a calculated measure of central sensitivity to thyroid hormones. It describes how “correctly” the pituitary keeps TSH for a given level of free T4.

The index was proposed by the Laclaustra group in 2019 as a more robust alternative to the earlier TSHI. Normally it is centered around zero.

Reference ranges

Formula via the cumulative distribution functions (CDF) of free T4 and the logarithm of TSH:

Formula (TFQI)F(FT4) − (1 − F(ln TSH))
Mean0
Reference (±1 SD·2)−0.74 … +0.74
Important: The parametric variant (PTFQI) uses normal distributions of the reference population; the standard deviation ≈ 0.37.

What an elevated level means

A high PTFQI means reduced sensitivity to thyroid hormones: the body behaves as if it has “too little” hormone despite normal tests. In large studies, high values are linked to obesity, hypothyroidism, metabolic syndrome, diabetes and higher mortality.

What a low level means

A low (negative) PTFQI reflects increased sensitivity to thyroid hormones. Clinically this is usually less significant than high values; a lowered index is sometimes seen with certain psychotropic drugs.

How the test is done

There is no separate test: PTFQI is computed from TSH and free T4 measured at the same time using reference distributions. Together with TSHI it belongs to the sensitivity indices, whereas SPINA-GT and SPINA-GD assess the gland itself and hormone conversion.

What affects the value

  • The units and measurement method for free T4 and TSH must match the reference population.
  • Taking thyroid medication and an unstable thyroid function distort interpretation.
  • The index is validated for adults with formally normal thyroid function (euthyroidism).

Calculate using this marker

Calculators where PTFQI (Parametric Thyroid Feedback Quantile-based Index) is used directly:

Thyroid Integral Index Assessing central and peripheral sensitivity to thyroid hormones Open Thyroid Function TSH, free T4 and T3 panel: hormone status and the likely diagnosis Open

Frequently asked questions

What does a high PTFQI show?

Reduced sensitivity to thyroid hormones. Even with formally normal TSH and free T4, a high index has been associated in studies with obesity, metabolic syndrome and diabetes.

How is PTFQI different from TSHI?

Both assess sensitivity to hormones, but PTFQI is built on the quantiles of a reference population and is considered more robust to extreme values. TSHI is an earlier formula based on a logarithmic model.

Related terms

TSH (Thyroid-stimulating hormone) The pituitary hormone that controls the thyroid gland Free thyroxine (T4) The main thyroid hormone TSHI (Thyroid Sensitivity Index) The adequacy of TSH to the free-T4 level SPINA-GT (secretory capacity) The gland's maximum thyroxine output SPINA-GD (deiodinase activity) Peripheral conversion of T4 → T3 Thyroid gland The endocrine organ that governs metabolism Metabolic syndrome A cluster of cardiometabolic risk factors

Sources

  1. Thyroid Feedback Quantile-based Index — Wikipedia
  2. Elevated PTFQI is associated with atrial fibrillation. Frontiers in Endocrinology, 2023
info
This content is educational and does not replace consultation with a physician. Reference ranges may vary depending on the laboratory and method — rely on the ranges stated on your own test report.
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