THY 9 values Updated Apr 29, 2026

Thyroid Panel

A thyroid panel measures the values most informative about thyroid function: TSH (the signal from the pituitary), free T4 (the thyroid's main output), free T3 (the active form of thyroid hormone), and often thyroid antibodies (which describe whether autoimmune activity is involved). TSH and free T4 are usually read together — interpreting either alone misses the relationship between them. BloodSight charts every thyroid panel across visits so the pattern across all four values is visible side by side.

Read the Thyroid Panel guide

How a Thyroid Panel Reads Thyroid Function

A thyroid panel describes a feedback loop between two glands. The pituitary releases TSH to tell the thyroid how hard to work; the thyroid responds by producing T4 (mostly) and T3 (some), which then circulate and signal back to the pituitary to tune TSH. When the loop works smoothly, TSH and free T4 sit in their reference ranges and the body's thyroid hormone supply matches demand. When the loop is disrupted — by autoimmune activity, gland damage, or medication — the values shift. TSH and free T4 are usually read together because their relationship is more informative than either value alone.

Reasons a Thyroid Panel Gets Ordered

Thyroid panels are ordered to screen for thyroid dysfunction, monitor an existing thyroid condition, follow response to thyroid medication (levothyroxine, methimazole), or work up symptoms that overlap with thyroid disease (fatigue, weight changes, hair changes, temperature regulation, mood changes). They're also routinely included in pregnancy workups because thyroid status during pregnancy affects both maternal and fetal outcomes.

Tests Found in a Thyroid Panel

The standard thyroid panel reports TSH, free T4, and free T3. Some labs also report total T4 and total T3 (the bound + free forms together), but the free fractions are usually more informative. A 'comprehensive' thyroid panel adds antibodies — anti-TPO (thyroid peroxidase antibodies) and anti-thyroglobulin antibodies — which describe whether autoimmune activity is involved in any abnormality. Reverse T3 is occasionally ordered separately. Pregnancy-trimester-specific reference ranges differ from the standard adult ranges.

How to Read TSH, T4, and T3 Together

Thyroid panel values describe a feedback loop: the pituitary signals (TSH), the thyroid responds (T4, T3). Reading any value alone misses the relationship — and that relationship is what carries most of the interpretive weight.

  1. 1

    TSH — the pituitary signal

    TSH is the most sensitive single thyroid marker because the pituitary tunes its TSH output before circulating thyroid hormones shift noticeably. TSH high suggests the pituitary is calling for more thyroid hormone production; TSH low suggests the opposite.

  2. 2

    Free T4 — the thyroid output

    Free T4 is the main hormone the thyroid produces, in its active (unbound) form. Free T4 is read alongside TSH — high TSH + low free T4 = overt hypothyroidism; low TSH + high free T4 = overt hyperthyroidism; high TSH + normal free T4 = subclinical hypothyroidism.

  3. 3

    Free T3 — the more active fraction

    Most circulating T3 is converted from T4 in peripheral tissues. Free T3 sometimes shifts with TSH and free T4, and sometimes describes a separate conversion-stage pattern. Free T3 is more variable across draws than TSH.

  4. 4

    Antibodies (anti-TPO, anti-Tg)

    When ordered, thyroid antibodies describe whether autoimmune activity is part of the thyroid picture. Anti-TPO is the most commonly tested. Low-titre antibodies can be present in healthy people; persistent high-titre antibodies usually mean more.

  5. 5

    The TSH–free T4 relationship is the headline

    The interpretation framework comes down to where TSH and free T4 sit relative to each other. Many endocrinology references suggest a narrower TSH window (often 1.0–2.5 mIU/L) than the standard 0.4–4.5 mIU/L lab reference range as an optimal target. The trajectory across multiple panels matters more than any single TSH reading.

Read the full Thyroid Panel guide

Thyroid Panel Reference Ranges

Thyroid laboratories use a wide reference range for TSH (typically 0.4–4.5 mIU/L) that has been debated for decades — many endocrinology references argue for a narrower 1.0–2.5 mIU/L target. The values below show the standard cutoffs printed on most lab reports.

Test Normal range (Adult) Unit Flagged when
Thyroid Stimulating Hormone TSH 0.4–4.5 mIU/L < 0.4 or > 4.5
Free Thyroxine Free T4 0.8–1.8 ng/dL < 0.8 or > 1.8
Free Triiodothyronine Free T3 2–4.4 pg/mL < 2 or > 4.4
Total Thyroxine T4 5–12 mcg/dL < 5 or > 12
Anti-Thyroid Peroxidase Antibodies Anti-TPO 0–34 IU/mL < 0 or > 34
Anti-Thyroglobulin Antibodies Anti-Tg 0–4 IU/mL < 0 or > 4
Reverse Triiodothyronine rT3 9–24 ng/dL < 9 or > 24
Thyroglobulin Tg 0–55 ng/mL < 0 or > 55
Thyroid-Binding Globulin TBG 12–26 mg/L < 12 or > 26

What Moves Thyroid Values

Thyroid panel values shift with iodine intake, autoimmune activity, several common medications (especially biotin and amiodarone), pregnancy, and time of day for the draw. TSH and free T4 are usually read together — interpreting either value alone misses the relationship between them.

Common factors for high values

Common factors for low values

All Thyroid Panel Values

Thyroid Stimulating Hormone

TSH

Thyroid Stimulating Hormone (TSH) is a lab value that measures the amount of TSH in blood and is often used in thyroid panel testing. On a Thyroid Stimulating Hormone on a blood test or lab report, the result helps describe how much TSH is circulating and how it compares with the Thyroid Stimulating Hormone reference range. High TSH and low TSH values can both reflect changes in hormone balance or testing conditions.

Adult Male mIU/L
0.4
4.5

Free Thyroxine

Free T4

Free Thyroxine (Free T4) is the unbound portion of thyroxine circulating in blood. On a Free T4 blood test, it reflects the hormone available for tissue use and helps describe thyroid status on a lab report. The Free Thyroxine result is usually reviewed with TSH and other thyroid markers to give a fuller picture.

Adult Male ng/dL
0.8
1.8

Free Triiodothyronine

Free T3

Free Triiodothyronine (Free T3), or Free T3, is the unbound portion of the thyroid hormone triiodothyronine measured in blood. It is used in a thyroid panel to show how much hormone is available to tissues at the time of the Free T3 test. On a Free Triiodothyronine on a lab report, the result is interpreted with other thyroid markers and the Free Triiodothyronine reference range.

Adult Male pg/mL
2
4.4

Total Thyroxine

T4

Total Thyroxine (T4) is a blood measurement of the total amount of thyroxine, a thyroid hormone circulating in the bloodstream. It is reported as T4 on a lab report or blood test and helps describe thyroid hormone levels in context with other results. Because it measures total hormone, binding proteins can influence the Total Thyroxine test result.

Adult Male mcg/dL
5
12

Anti-Thyroid Peroxidase Antibodies

Anti-TPO

Anti-Thyroid Peroxidase Antibodies (Anti-TPO) is a blood marker that measures antibodies directed against thyroid peroxidase, an enzyme found in thyroid tissue. On an Anti-TPO blood test, higher values suggest more thyroid-directed immune activity, while lower values suggest less. Anti-TPO is often reviewed on a lab report as part of a thyroid panel to help show the broader pattern of thyroid-related blood results.

Adult Male IU/mL
0
34

Anti-Thyroglobulin Antibodies

Anti-Tg

Anti-Thyroglobulin Antibodies (Anti-Tg) are immune proteins measured in blood that bind to thyroglobulin, a protein made by the thyroid. On a lab report, Anti-Tg helps describe whether the body is making antibodies against this thyroid-related protein. In a thyroid panel, it adds context to other thyroid markers and can help explain why the result is being reviewed.

Adult Male IU/mL
0
4

Reverse Triiodothyronine

rT3

Reverse Triiodothyronine (rT3) is a thyroid hormone-related lab value often reported as rT3. It reflects how much reverse T3 is present in blood and is usually interpreted as part of a thyroid panel or a Reverse Triiodothyronine test. On a lab report, rT3 helps describe thyroid hormone balance, and the Reverse Triiodothyronine normal range can vary by lab method.

Adult Male ng/dL
9
24

Thyroglobulin

Tg

Thyroglobulin (Tg) is a thyroid-related protein that can be measured in blood and reported on a lab report or blood test. It is mainly used as a marker of thyroid tissue activity, and the Tg test helps show how much Tg is present in circulation. On a thyroid panel, the Thyroglobulin normal range and any change in Tg are interpreted with the rest of the results.

Adult Male ng/mL
0
55

Thyroid-Binding Globulin

TBG

Thyroid-Binding Globulin (TBG) is a blood protein that carries thyroid hormones through the bloodstream, and the TBG test measures how much of that transport protein is present. On a lab report, TBG helps describe thyroid hormone binding in blood rather than thyroid hormone production itself. The Thyroid-Binding Globulin (TBG) value is usually read with other thyroid panel results to understand the overall pattern.

Adult Male mg/L
12
26

Compare values in this panel

How values in this panel relate to each other and what their differences mean.

Timing and Prep for a Thyroid Panel

Thyroid panels do not require fasting, but timing matters. TSH has a natural circadian rhythm — peaking overnight and falling through the morning — so consistent draw time across panels makes trajectories more readable. Biotin (vitamin B7), commonly found in hair/nail/skin supplements, can interfere with several thyroid immunoassays and must be paused for 48–72 hours before the draw. Recent illness can transiently shift TSH; if the goal is baseline assessment, the panel is usually drawn well after recovery.

Thyroid Panel Questions

What does a thyroid panel measure?
A thyroid panel measures the values that describe thyroid function: TSH (the signal from the pituitary telling the thyroid how hard to work), free T4 (the main hormone the thyroid produces), free T3 (the more active form, mostly converted from T4 in peripheral tissues), and often thyroid antibodies (anti-TPO and anti-thyroglobulin) which describe whether autoimmune activity is involved. TSH and free T4 are usually read together because their relationship is more informative than either value alone.
What does TSH stand for and why is it tested?
TSH stands for thyroid-stimulating hormone. It's produced by the pituitary gland, not the thyroid itself, and it tells the thyroid how hard to work. When circulating thyroid hormones are low, TSH rises to stimulate more production; when they are high, TSH falls. Because TSH responds before T4 and T3 shift noticeably, it's the most sensitive single signal of thyroid status — which is why it's the most commonly ordered thyroid test.
What's the difference between TSH and free T4?
TSH is the pituitary's signal to the thyroid; free T4 is the thyroid's main output. The two are read together because their relationship matters: high TSH with low free T4 describes hypothyroidism (the pituitary is shouting because the thyroid is underperforming), while low TSH with high free T4 describes hyperthyroidism (the pituitary is silent because the thyroid is overproducing). High TSH with normal free T4 describes a different pattern called subclinical hypothyroidism.
What does a high TSH mean?
A high TSH means the pituitary is signalling for more thyroid hormone production than the thyroid is providing. The most common cause is reduced thyroid output (hypothyroidism), often from autoimmune thyroiditis. TSH between the upper reference limit and ~10 mIU/L with normal free T4 is described as subclinical; TSH above ~10 mIU/L is generally overt. A single mildly elevated TSH is often repeated a few weeks later because TSH has natural circadian and day-to-day variation.
What are optimal TSH levels?
Standard laboratory TSH reference ranges are typically 0.4–4.5 mIU/L and have been debated for decades. Many endocrinology and lifestyle-medicine references suggest a narrower 1.0–2.5 mIU/L target as optimal, particularly in people without overt thyroid disease. Optimal targets describe what's associated with the smoothest thyroid signalling, which is not the same as the laboratory's printed reference range.
What causes high TSH?
TSH rises when the thyroid is producing less hormone than the pituitary is calling for. The most common reason is autoimmune thyroiditis (Hashimoto's), where the thyroid is gradually damaged. Other causes include iodine status, thyroid surgery or radiation, and certain medications including lithium and amiodarone. Pregnancy can also shift TSH, with trimester-specific reference ranges. Each component biomarker page in BloodSight describes the factors most associated with that specific value.
What are thyroid antibodies?
Thyroid antibodies are immune-system proteins that target thyroid tissue. The two most commonly tested are anti-TPO (thyroid peroxidase antibodies) and anti-thyroglobulin antibodies. Their presence describes autoimmune activity against the thyroid, which is the underlying mechanism in Hashimoto's thyroiditis (most common cause of hypothyroidism) and Graves' disease (most common cause of hyperthyroidism). Low-titre antibodies can also be present in people without thyroid dysfunction.
Should I pause biotin before a thyroid panel?
Yes — biotin (vitamin B7), commonly found in hair/skin/nail supplements, can interfere with several thyroid immunoassays. It can falsely lower TSH and falsely raise free T4 and free T3 measurements, producing a pattern that looks like hyperthyroidism on paper. Most labs recommend pausing biotin supplements for 48–72 hours before the draw. The lab requisition usually flags this if it applies to your specific assay.
Do I need to fast for a thyroid panel?
Thyroid panels do not require fasting. The values aren't significantly affected by recent meals. Timing of the draw matters more than fasting — TSH has a natural circadian rhythm (peaking overnight, falling through the morning), so consistent draw time across panels makes trajectories more readable.
How does BloodSight track thyroid values over time?
BloodSight charts every TSH, free T4, free T3, and thyroid antibody value across all your uploaded thyroid panels in one timeline. Thyroid values are most informative as a trajectory — TSH especially has natural day-to-day variation, and a single value often means less than the trend across consecutive panels drawn at consistent times.

Panels Drawn With a Thyroid Workup

A thyroid panel is often ordered when something on a routine workup raises a question, or alongside a broader hormone or nutrient evaluation. The panels below most often appear on the same requisition.

CMP

Comprehensive Metabolic Panel (CMP)
HRM

Hormone Panel
VIT

Vitamins & Nutrients

Disclaimer

This content is for informational and educational purposes only. It is not intended as medical advice, diagnosis, or treatment recommendation. Reference ranges may vary by laboratory. Always discuss your results with a qualified healthcare professional.