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PTFQI-FT3

Parametric thyroid feedback quantile-based index for FT3
Estimated pituitary TSH sensitivity to free T3. This is a newer, less validated index, but may add value in some contexts.
Do not confuse with PTFQI, the better-validated index that uses free T4 instead of free T3.
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Value
Unit

PTFQI-FT3 ranges

According to Kratzsch et al. (2005), PTFQI-FT3 should be between -0.7 and 0.7:
−0.7
0.7
Risk Scale
Optimal range for PTFQI-FT3 appears to be between -0.4 and 0.4:
−1
−0.7
−0.4
0.4
0.7
1
Why this optimal range?
Ranges are based on standard deviations from the mean. Values in red (±2 SD) indicate significant deviation from expected pituitary-thyroid feedback; values in yellow (±1-2 SD) indicate moderate deviation.

Estimated pituitary TSH sensitivity to free T3. This is a newer, less validated index, but may add value in some contexts.

Its clinical value is debated, because negative feedback also depends on locally generated T3 (within the hypothalamus/pituitary) and may not be fully captured by serum FT3 alone.

The parameters used to calculate PTFQI-FT3 were estimated from the medians and 95% reference intervals reported by Kratzsch et al. (2005) for a reference cohort selected using NACB criteria and normal thyroid ultrasound.

PTFQI-FT3 interpretation

What a low value may mean:

Low PTFQI-FT3 means that TSH is lower than expected for the given FT3, reflecting apparent pituitary over-sensitivity or impaired TSH secretion. Very low values may support a diagnosis of central (secondary/tertiary) hypothyroidism.

What a high value may mean:

High PTFQI-FT3 indicates TSH is higher than expected for the given FT3, most commonly seen in subclinical hypothyroidism or reduced apparent pituitary sensitivity.

Individual Biomarkers

See how each biomarker is interpreted on its own.

TSH: 000 µIU/mL

Thyroid Stimulating Hormone is a pituitary signal indicating how much thyroid hormone is requested.
0.3
1
2.5
4.4
10

fT3: 000 pg/mL

Free T3 is the active thyroid hormone driving metabolism (the "gas pedal").
0
2
2.8
4
4.4
7

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