Free T4
Standard Reference Range
See Lab Results
Optimal Cognitive Range
1.0–1.5 ng/dL
Clinical Significance
Thyroid hormone precursor — low levels indicate hypothyroidism
Clinician Discussion
Often not included in basic screening panels; request if experiencing brain fog or related symptoms. Optimal ranges for cognitive performance may differ from standard laboratory ranges.
Potentially Related Causes
Abnormal results may indicate involvement of these underlying conditions:
Click any cause above to learn about symptoms, tests, and evidence-based interventions.
This information is for educational purposes only. Always consult with a qualified healthcare professional.