A thyroid panel is a group of blood tests that shows how well your thyroid gland is working and whether the signal your brain sends to control it is in balance. It almost always starts with thyroid-stimulating hormone (TSH), usually adds free thyroxine (free T4), and sometimes includes free or total triiodothyronine (T3) and thyroid antibodies. No single number tells the whole story: an abnormal TSH shows that something is off, while free T4 and T3 help explain what is happening and why.
In this article you’ll learn what each test measures, the typical adult ranges, how to read TSH, free T4 and free T3 together, what can distort your results, how pregnancy, age and treatment change the picture, and when to talk to your doctor.
What a thyroid panel measures
Your thyroid is a butterfly-shaped gland at the front of your neck. It releases thyroxine (T4), its main hormone, and triiodothyronine (T3), the more active form, which together set the pace of your metabolism.
The feedback loop between your brain and your thyroid
The pituitary gland at the base of your brain releases TSH to tell the thyroid how much hormone to make. When thyroid hormone drops, the pituitary makes more TSH; when it is high, the pituitary makes little or no TSH, as MedlinePlus explains. This seesaw is why a high TSH most often points to an underactive thyroid and a low TSH usually points to an overactive one, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
Tests usually included
- TSH: the first test in almost every thyroid workup. Explore this single marker in detail by reading our guía sobre el análisis de TSH en sangre.
- Free T4: the unbound thyroxine that can enter tissues. NIDDK notes that many clinicians prefer it to total T4 because changes in blood proteins don’t affect it. For a closer look at this result, open our free T4 results guide.
- Free T3 or total T3: mainly useful when an overactive thyroid is suspected. The American Thyroid Association (ATA) notes that T3 rarely helps diagnose an underactive thyroid and that free T3 is often less reliable. Read the specifics by visiting our guía de resultados de T3 libre.
- Thyroid antibodies: added to a thyroid panel when an autoimmune cause is suspected, as described below.
Why your doctor may order one
Doctors order a thyroid panel when symptoms suggest the gland is too slow (tiredness, feeling cold, constipation, weight gain) or too fast (weight loss, a fast heartbeat, nervousness, trouble tolerating heat), to monitor treatment, and before or during pregnancy. Mayo Clinic notes that diagnosis rests mainly on blood tests because these symptoms overlap with many other conditions.
If long-lasting exhaustion is your main concern, review our guía sobre el síndrome de fatiga crónica. If low mood is what brought you to the test, take a moment to read our depression guide.
Normal ranges for TSH, free T4 and free T3
The ranges below come from the MedlinePlus Medical Encyclopedia, reviewed in 2026. Each laboratory sets its own range based on its testing method, so always compare your result with the range printed on your thyroid panel report.
| Prueba | Qué refleja | Rango habitual en adultos | Good to know |
|---|---|---|---|
| TSH | The pituitary’s signal to the thyroid | 0.4 to 4.8 µU/mL (the same value in mIU/L) | Some labs use an upper limit of up to about 7 for older adults |
| T4 libre | Unbound thyroxine available to tissues | 0.8 to 1.9 ng/dL (10.3 to 24.5 pmol/L) | Less affected by carrier proteins than total T4 |
| T3 libre | Unbound triiodothyronine, the active hormone | 210 to 440 pg/dL (3.2 to 6.8 pmol/L), about 2.1 to 4.4 pg/mL | Many US labs report pg/mL; ranges are age-specific under 20 |
| Total T3 | Bound plus free T3 | 78 to 158 ng/dL (1.2 to 2.4 nmol/L) | Raised by pregnancy, birth control pills and estrogen |
For TSH, µU/mL and mIU/L are interchangeable.
Why TSH comes first
NIDDK describes TSH as the test usually checked first. Because the pituitary reacts to small shifts in thyroid hormone, TSH often becomes abnormal before free T4 leaves its range, which is what defines the subclinical forms described below. An abnormal TSH cannot reveal the cause on its own, so MedlinePlus notes that T4, T3 and antibody tests usually follow.
How to read TSH, free T4 and free T3 together
Doctors read a thyroid panel as a pattern rather than as separate numbers. The table summarizes common combinations described by NIDDK, Mayo Clinic, the ATA and MedlinePlus. It is a reading aid, not a diagnosis: your doctor also weighs your symptoms, medicines and history.
| TSH | T4 libre | T3 libre | Lo que suele indicar |
|---|---|---|---|
| Alto | Bajo | Normal o baja | Underactive thyroid (primary hypothyroidism), often from Hashimoto’s disease |
| Alto | Normal | Normal | Subclinical hypothyroidism, a mild form that often causes no clear symptoms |
| Bajo | Alto | Alta o normal | Overactive thyroid (hyperthyroidism), for example Graves’ disease, toxic nodules, thyroiditis or too much thyroid medicine |
| Bajo | Normal | Alto | T3 thyrotoxicosis, a less common form of overactive thyroid |
| Bajo | Bajo | Bajo o normal | Underactive thyroid caused by a pituitary problem (central hypothyroidism), which is rare |
| Normal | Normal | Normal | The thyroid is usually working normally |
| Normal o alta | Alto | Alta o normal | Results that don’t fit together and may point to lab interference or a rare condition |
High TSH: an underactive thyroid
Mayo Clinic says a high TSH with a low free T4 confirms hypothyroidism, and MedlinePlus lists Hashimoto’s disease as a common cause. When TSH is high but free T4 and free T3 stay in range, the pattern is called subclinical hypothyroidism and usually causes no noticeable symptoms. A high TSH is normally repeated along with free T4 before any decision. Review symptoms and treatment options by reading our hypothyroidism guide.
Low TSH: an overactive thyroid
A low TSH with a high free T4 is the typical pattern of hyperthyroidism, Mayo Clinic explains. MedlinePlus lists Graves’ disease, toxic nodular goiter, excess iodine (for example from CT contrast dye) and too much thyroid medicine among the causes. Free T4 sometimes stays normal while T3 is high, which is why NIDDK notes that measuring both can help. Learn how this condition is treated by exploring our hyperthyroidism guide.
When TSH and free T4 are both low
La American Thyroid Association explains that a low TSH with a low free T4 suggests hypothyroidism caused by a pituitary gland that sends too little TSH, a cause MedlinePlus describes as rare. Severe illness and glucocorticoid medicines can also lower these values for a while, so the result is usually rechecked.
When the results don’t fit together
When free T4 and free T3 are high but TSH is normal or high, a 2026 European Thyroid Association guideline states that lab interference must be excluded before rare conditions such as resistance to thyroid hormone or a TSH-secreting pituitary tumor are considered. Interference can come from antibodies, inherited binding-protein variants, medicines or biotin, and your doctor may ask the lab to repeat the test with a different method.
Thyroid antibodies: finding the cause
When a thyroid panel points to a thyroid problem, antibody tests help identify an autoimmune cause. NIDDK lists them as tools for diagnosing Hashimoto’s disease and Graves’ disease.
- Thyroid peroxidase (TPO) and thyroglobulin antibodies: according to the ATA, positive results in someone with hypothyroidism point to Hashimoto’s thyroiditis. Understand what a positive result means by reading our anti-TPO antibody guide.
- TSI (thyroid-stimulating immunoglobulin): the antibody that drives the gland to overwork in Graves’ disease.
- TRAb (TSH receptor antibodies): a test that detects both stimulating and blocking antibodies. The ATA notes it can help judge treatment response, decide when to stop antithyroid medicine and assess the risk to a baby during pregnancy.
The ATA adds that tracking antibody levels over time does not help monitor treatment; TSH and free T4 remain the monitoring tests.
What can throw off your thyroid test results
Several everyday factors can push a thyroid panel out of range without any thyroid disease.
Suplementos de biotina
Biotin (vitamin B7), found in many supplements and multivitamins, can interfere with the lab methods used for TSH and free T4 and make results look abnormal when they are not, according to MedlinePlus and the ATA. The ATA suggests stopping biotin for 2 days before a thyroid blood draw, while Mayo Clinic notes that some clinicians ask for 3 to 5 days.
Medicines
MedlinePlus lists amiodarone, lithium, dopamine, potassium iodide, glucocorticoids such as prednisone, opioids and some cancer drugs among the medicines that can change TSH or thyroid hormone results. Birth control pills and estrogen can raise total T3. Never stop a medicine on your own.
Illness, fasting and time of day
Severe illness can lower T4 and T3 temporarily, and MedlinePlus notes that malnutrition or fasting can lower free T4. TSH also varies over the day, so early-morning testing gives the most consistent results.
Changes in carrier proteins
Pregnancy and birth control pills raise the proteins that carry thyroid hormone, which increases total T4 and T3 even when the thyroid is working normally, according to the ATA. That is why free T4 is preferred. Inherited changes in a binding protein, as well as liver or kidney disease, can also affect results. Learn about the main carrier protein by reading our thyroxine-binding globulin guide.
Pregnancy, age and treatment: special situations
During pregnancy
MedlinePlus notes that TSH is often a little low in the first three months of pregnancy, that the normal range differs during pregnancy and that a provider may recommend thyroid hormone even when TSH is within the usual range. Because pregnancy raises total T4 and T3, the ATA recommends relying on TSH and free T4.
In older adults
TSH tends to rise with age. MedlinePlus notes that it may be higher in people over 80 who have no thyroid disease, and some labs use an upper limit of up to about 7 for older adults. A single adult range can therefore label a healthy older person as having subclinical hypothyroidism.
If you take thyroid medicine
For people taking levothyroxine, TSH is the main monitoring test. Mayo Clinic says it is typically checked 6 to 8 weeks after starting treatment, again about 6 months later and then about once a year. Levothyroxine works best on an empty stomach, 30 to 60 minutes before eating, and iron or calcium supplements, some antacids, large amounts of soy and a high-fiber diet can reduce its absorption.
If you take iron, check your stores by reading our iron panel guide. If you take calcium, keep track of your levels by opening our total calcium test guide.
How to prepare for a thyroid panel
- List all your medicines and supplements for your provider, especially biotin.
- Book an early-morning appointment if you can.
- Fasting isn’t usually needed for a thyroid panel alone, but MedlinePlus notes that you may need to fast for several hours if other blood tests are drawn at the same time.
- If you take levothyroxine, ask whether to take your dose before or after the draw, and keep that timing the same for every test.
- Mention a pregnancy or pregnancy plans, since different ranges apply.
Cuándo hablar con tu médico sobre tus resultados
Contact your clinician before your routine follow-up if:
- your TSH or free T4 is out of range and you have a racing or irregular heartbeat, unexplained weight loss, a tremor or marked fatigue;
- you are pregnant or trying to conceive and your TSH is outside your lab’s range;
- your thyroid panel results don’t fit together, such as a high free T4 with a normal or high TSH;
- you take thyroid medicine and your TSH has moved out of range, or you recently changed brand or dose;
- you take biotin or one of the medicines listed above and the abnormal result was unexpected.
A single, slightly abnormal TSH is often repeated before any treatment starts. Midlife hot flashes, poor sleep and mood changes can also have other causes, which you can explore by reading our menopause guide.
Últimos avances científicos
Age-specific ranges could prevent overdiagnosis
A 2024 Dutch study in the journal Thyroid analyzed 7.6 million TSH results from 13 laboratories. The upper limit of a normal TSH rose from about age 60 in men and from about age 50 in women. Using age-specific ranges, meaning ranges calculated for each age group instead of one range for all adults, reduced the number of older people classed as having hypothyroidism. What this means for you: a slightly high TSH on a thyroid panel in your 60s or 70s may be normal for your age, so ask whether your lab takes age into account.
Treating a mildly high TSH in older adults remains an open question
A 2024 systematic review, a study that pools earlier research, found only seven studies on people over 65 with subclinical hypothyroidism and no clear difference in heart outcomes between those treated with levothyroxine and those who were not. A 2026 UK analysis of more than 22,000 adults over 50, based on health records rather than a randomized trial, linked long-term treatment with fewer heart problems, but only when TSH was above the age-specific range and after at least five years. What this means for you: if your TSH is only slightly high, treatment is a personal decision to make with your doctor.
New guidance on lab interference, including biotin
In 2026, the European Thyroid Association published a guideline asking clinicians to rule out interference from antibodies, inherited binding-protein variants, medicines and biotin before diagnosing rare thyroid conditions. A 2025 laboratory study found that very high blood biotin levels shifted several test results by about a fifth with older reagents, including falsely high free T4 values, while newer reagent versions tolerated much more biotin. What this means for you: mention any biotin or multivitamin before your test, and ask about interference if your results don’t match how you feel.
Levothyroxine before and during pregnancy
A 2024 meta-analysis of randomized controlled trials, studies in which treatment is assigned by chance, looked at women with subclinical hypothyroidism. Levothyroxine taken before conception did not improve pregnancy or live birth rates or reduce miscarriages. Taken during pregnancy, it appeared to lower the risk of preterm birth only in women whose TSH was above 4.0. What this means for you: treatment around pregnancy depends on your exact TSH level and history, so review your results with your obstetric team.
Thyroid medicine is not a weight-loss treatment
A 2026 review of 35 studies including 1,116 people with hypothyroidism found that levothyroxine led to only small weight changes in overt hypothyroidism and no significant change in weight or body fat in subclinical hypothyroidism. The authors conclude that it must not be prescribed for weight loss. What this means for you: bringing thyroid levels back to normal matters for your health, but it may not reverse weight changes on its own.
Glosario
| Término | Definición |
|---|---|
| TSH (hormona estimulante del tiroides) | A hormone made by the pituitary gland that tells the thyroid how much hormone to produce. It rises when thyroid hormone is low and falls when it is high. |
| T4 libre (tiroxina libre) | The share of the main thyroid hormone that is not attached to proteins and can enter the body’s tissues. |
| Free T3 (free triiodothyronine) | The unbound share of the most active thyroid hormone, made by the thyroid and from T4 in the tissues. |
| Glándula pituitaria | A small gland at the base of the brain that controls several other glands, including the thyroid. |
| Hipotiroidismo | An underactive thyroid that makes too little hormone, usually shown by a high TSH and a low free T4. |
| Hipertiroidismo | An overactive thyroid that makes too much hormone, usually shown by a low TSH and a high free T4 or T3. |
| Hipotiroidismo subclínico | A mild form of underactive thyroid in which TSH is high but free T4 and T3 are still in the normal range. |
| Hashimoto’s disease | An autoimmune condition in which the immune system attacks the thyroid, and a common cause of an underactive thyroid. |
| Enfermedad de Graves | An autoimmune condition in which antibodies push the thyroid to make too much hormone. |
| Biotin | Vitamin B7, a supplement ingredient that can interfere with some lab methods and produce misleading thyroid results. |
Preguntas frecuentes
Do I need to fast for a thyroid blood test?
Usually not. A thyroid panel on its own does not require fasting, but MedlinePlus notes that you may need to fast for several hours if other blood tests, such as glucose or cholesterol, are drawn at the same visit. Check the instructions from your provider or lab, and take your usual medicines unless you are told otherwise.
¿Cuál es el mejor momento del día para hacerse una analítica de tiroides?
Early morning. TSH levels change over the course of the day, so MedlinePlus recommends early-morning testing for the most consistent results. If you have regular follow-up tests, try to book them at a similar time each visit so the numbers are easier to compare.
What can affect thyroid test results?
Biotin supplements, several medicines (such as amiodarone, lithium, glucocorticoids and estrogen), severe illness, fasting, pregnancy and inherited changes in thyroid binding proteins can all shift results. Tell your clinician about every medicine and supplement before the test, and never stop a prescribed drug without asking first.
What are the 5 thyroid tests?
There is no official list of five, but the tests most often grouped together are TSH, free T4, total or free T3, thyroid peroxidase (TPO) antibodies and TSH receptor antibodies (TRAb or TSI). Most people start with TSH alone or TSH plus free T4, and the other tests are added depending on the results and symptoms.
Do normal TSH levels change with age?
Yes. TSH tends to rise with age, and MedlinePlus notes that it may be higher in people over 80 without thyroid disease. A large 2024 study found that the upper limit of normal TSH starts rising from around age 50 in women and 60 in men. Some laboratories already use higher upper limits for older adults.
Is a normal TSH level different for women?
Adult reference ranges are generally the same for men and women, but the picture changes during pregnancy. TSH is often a little low in the first trimester, and pregnancy-specific ranges apply. Thyroid problems are also more common in women, so tell your clinician if you are pregnant, planning a pregnancy or recently gave birth.
Fuentes
- MedlinePlus, National Library of Medicine — TSH (Thyroid-stimulating hormone) Test — MedlinePlus Lab Tests, updated 2024 — medlineplus.gov
- MedlinePlus Medical Encyclopedia, National Library of Medicine — TSH test — reviewed 2026 — medlineplus.gov
- MedlinePlus Medical Encyclopedia, National Library of Medicine — Free T4 test — reviewed 2026 — medlineplus.gov
- MedlinePlus Medical Encyclopedia, National Library of Medicine — T3 test — reviewed 2026 — medlineplus.gov
- Instituto Nacional de Diabetes y Enfermedades Digestivas y Renales — Pruebas de tiroides — Información de salud del NIDDK — niddk.nih.gov
- Mayo Clinic Staff — Hypothyroidism (underactive thyroid): Diagnosis and treatment — Mayo Clinic — mayoclinic.org
- Mayo Clinic Staff — Hyperthyroidism (overactive thyroid): Diagnosis and treatment — Mayo Clinic — mayoclinic.org
- American Thyroid Association — Thyroid Function Tests — ATA Patient Information — thyroid.org
- Jansen HI, Dirks NF, et al. — Age-Specific Reference Intervals for Thyroid-Stimulating Hormones and Free Thyroxine to Optimize Diagnosis of Thyroid Disease — Thyroid, 2024 — doi.org/10.1089/thy.2024.0346
- Holley M, Razvi S, et al. — Cardiovascular and bone health outcomes in older people with subclinical hypothyroidism treated with levothyroxine: a systematic review and meta-analysis — Systematic Reviews, 2024 — doi.org/10.1186/s13643-024-02548-7
- Holley M, Razvi S, et al. — Assessing the Cardiovascular Effects of Levothyroxine Use in an Ageing UK Population with Subclinical Hypothyroidism: Emulated Target Trial (ACEL-UK-ETT) — Thyroid, 2026 — doi.org/10.1177/10507256261426576
- Campi I, Feldt-Rasmussen U, et al. — 2026 ETA guideline on interference in immunoassay measurements used in assessment of thyroid function — European Thyroid Journal, 2026 — doi.org/10.1530/ETJ-26-0011
- Chiu KC, Jhan JR, et al. — Biotin interference in routine clinical immunoassays — Practical Laboratory Medicine, 2025 — doi.org/10.1016/j.plabm.2025.e00472
- Sankoda A, Suzuki H, et al. — Effects of Levothyroxine Treatment on Fertility and Pregnancy Outcomes in Subclinical Hypothyroidism: A Systematic Review and Meta-Analysis of Randomized Controlled Trials — Thyroid, 2024 — doi.org/10.1089/thy.2023.0546
- Kretli-Souza D, Meireles-Oliveira G, et al. — Levothyroxine monotherapy has limited effects on body composition in clinical and subclinical hypothyroidism: a systematic review and meta-analysis — Reviews in Endocrine and Metabolic Disorders, 2026 — doi.org/10.1007/s11154-026-10093-y
Lecturas recomendadas
- Check the gland that controls blood calcium next to your thyroid by reading our parathyroid hormone blood test guide.
- Explore another hormone released by the pituitary gland by opening our guía sobre los niveles de prolactina en sangre.
- Compare another hormone that shapes energy and metabolism by visiting our guía sobre el análisis de cortisol en sangre.
- Rule out a common vitamin cause of fatigue by reviewing our vitamin B12 blood test guide.
- Understand a bone condition linked to excess thyroid hormone by exploring our osteoporosis guide.
Entiende tus resultados de laboratorio con BloodSense
A thyroid panel only makes sense when TSH, free T4 and free T3 are read together, alongside your symptoms, medicines and any antibody results. BloodSense helps you understand your thyroid results and related blood tests in plain language, with the questions worth asking your doctor. It does not make a diagnosis and does not replace your doctor.
