Calculator Form
Formula Used
Marker status: A value below the selected low limit is low. A value above the selected high limit is high. Otherwise, it is within range.
Balance index: average absolute midpoint deviation multiplied by 33.33, then capped at 100.
Free T4 conversion: pmol/L = ng/dL × 12.87.
Free T3 conversion: pmol/L = pg/mL × 1.536.
Relative conversion ratio: converted FT3 in pmol/L divided by converted FT4 in pmol/L.
How to Use This Calculator
- Enter TSH, Free T4, and Free T3 from your lab report.
- Select the same units shown on your report.
- Enter the low and high reference limits printed by your lab.
- Add date, age, pregnancy status, symptoms, and notes if useful.
- Press Calculate to view the result below the header.
- Use CSV or PDF export for record keeping.
Example Data Table
| Scenario | TSH | Free T4 | Free T3 | Possible Pattern |
|---|---|---|---|---|
| Balanced sample | 2.10 mIU/L | 1.20 ng/dL | 3.10 pg/mL | Within selected ranges |
| Underactive sample | 8.20 mIU/L | 0.60 ng/dL | 2.00 pg/mL | Possible primary hypothyroid pattern |
| Overactive sample | 0.05 mIU/L | 2.20 ng/dL | 5.10 pg/mL | Possible hyperthyroid pattern |
| Discordant sample | 5.90 mIU/L | 2.10 ng/dL | 3.80 pg/mL | Needs clinical review |
Thyroid Testing Overview
The thyroid gland helps regulate energy use, temperature, heart rhythm, digestion, and general metabolism. Lab panels often include TSH, T4, and T3 because each marker describes a different part of thyroid signaling. TSH comes from the pituitary gland. It acts like a request signal. When circulating thyroid hormone is low, TSH may rise. When circulating hormone is high, TSH may fall.
Why T3, T4, and TSH Matter
T4 is the main hormone released by the thyroid. Much of it can convert into T3, which is more active in many tissues. A calculator can organize these values, but it cannot diagnose disease. Results must be reviewed with symptoms, medicines, pregnancy status, supplements, previous surgery, antibody tests, and local laboratory rules.
Understanding Pattern Notes
This tool compares each entered result with your selected low and high limits. It then labels each item as low, within range, or high. The summary pattern follows common screening logic. High TSH with low free T4 may suggest a primary underactive pattern. Low TSH with high T4 or T3 may suggest an overactive pattern. Normal values usually suggest no clear biochemical imbalance inside the selected limits.
Useful Advanced Options
Editable ranges are important because laboratories use different instruments and methods. Units also differ across reports. This page includes conversion support for free T4 and free T3, a relative T3 to T4 ratio, and a balance index. The index is not a medical score. It simply shows how far the three values sit from the midpoint of the selected ranges.
Safe Use
Use this calculator to prepare questions for a clinician. Bring the original report when possible. Do not adjust thyroid medicine from a web result alone. Biotin supplements, acute illness, pregnancy, iodine exposure, and several medicines can affect thyroid tests. Rechecking at the right time may be necessary. A clinician can connect the numbers with your history and decide whether more testing or treatment is needed.
For best tracking, use the same laboratory when possible. Record collection date, fasting state, dose timing, and recent supplement use. Trends can be more useful than one isolated value. Always compare this calculated pattern with the printed reference interval on your official report before making any health decision.
FAQs
1. What does this thyroid calculator do?
It compares TSH, Free T4, and Free T3 with your chosen ranges. It gives a possible pattern, basic ratio, and exportable report. It does not diagnose disease.
2. Should I use my lab reference range?
Yes. Use the reference limits printed on your report. Different laboratories may use different methods, units, and ranges.
3. Can this replace a doctor?
No. Thyroid results need symptoms, history, medicines, pregnancy status, and clinical review. Use the output as a discussion aid only.
4. Why are TSH and T4 both needed?
TSH reflects pituitary signaling. T4 reflects thyroid hormone output. Their relationship helps clinicians understand many common thyroid patterns.
5. Why include T3?
T3 may help clarify some overactive patterns. It can also provide extra context when TSH or T4 results are unclear.
6. What does a high balance index mean?
It means the entered values are farther from selected range midpoints. It is not a disease score or treatment target.
7. Can medicines affect these tests?
Yes. Thyroid medicine, biotin, iodine, steroids, amiodarone, and other factors may affect results. Ask a clinician before changing anything.
8. Why is the PDF generated in the browser?
The page creates a simple PDF from visible results. This keeps the tool easy to deploy and avoids extra server libraries.