Thyroid Lab Reference Range Comparison

TSH is a pituitary hormone that helps regulate the thyroid. It is commonly used as an initial thyroid function test, but interpretation also considers free T4 and clinical circumstances. American Thyroid Association: thyroid function tests

This tool compares TSH and optional free T4 with the laboratory reference intervals you enter. It reports whether each number is below, within or above its entered interval. It does not accept T3, supply an “optimal” hormone target, diagnose a condition or choose treatment. Use the result, lower limit and upper limit from the same report, in the same units. Do not mix a free T4 result with a total T4 range.

What Is TSH and What Do the Numbers Mean?

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Key Takeaway: TSH and free T4 are interpreted together. High TSH with low free T4 suggests primary hypothyroidism; low TSH with high free T4 suggests hyperthyroidism. Low TSH can also occur with a pituitary problem, so “low always means overactive” is incorrect. ATA test interpretation

Information on your report	What this tool does	What it cannot establish
TSH result and both interval limits	Compares the number with those limits	The cause of an abnormal result
Optional free T4 and both limits	Makes a separate interval comparison	A diagnosis from the combination
A value within an entered interval	Displays “within”	That symptoms have been explained
A value outside an entered interval	Displays “below” or “above”	How urgently treatment is needed
Missing or incompatible units	Requires you to check the report	A reliable comparison from mixed units

Reference interval versus treatment target: The entered laboratory interval is the comparator for this tool. It is not a prescription target. Copying a narrow interval from another website changes the comparison without providing evidence that it applies to you.

For example, a value of 6 compared with an entered interval of 1–5 is above that interval. This is an arithmetic example using invented numbers, not a thyroid reference range or an instruction to start medication. At an entered endpoint the tool reports “within,” matching its inclusive comparison rule.

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Note: The ATA explains the feedback relationship between the pituitary and thyroid, but it also describes exceptions and the importance of free T4. Do not reduce its guidance to one TSH cutoff that diagnoses every patient. ATA explanation

Hypothyroid vs. Hyperthyroid: Symptoms Compared

The following are examples described by the ATA, not a symptom score. Symptoms can overlap with other conditions and are not confirmation of thyroid disease. ATA hypothyroidism, ATA hyperthyroidism

Possible hypothyroid symptoms	Possible hyperthyroid symptoms
Feeling cold	Feeling hot and sweating
Fatigue	Difficulty sleeping
Constipation	Frequent bowel movements
Dry skin	Hand tremor
Forgetfulness	Anxiety or irritability

Bring a description of symptoms and the original laboratory report to your appointment. A comparison result cannot determine whether a symptom is caused by your thyroid. The ATA also notes that medicines and supplements, including biotin, can affect interpretation or testing. Tell the clinician what you take rather than changing it because of this page. ATA testing considerations

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Warning: This calculator compares lab values against the reference intervals you enter. It does not diagnose thyroid disease. Discuss abnormal results with your endocrinologist or primary care provider; symptoms, history, pregnancy and further testing can affect interpretation. ATA testing guidance

TSH During Pregnancy

Pregnancy changes thyroid testing context. The ATA explains that estrogen changes binding proteins and total hormone measurements; free hormone results must be considered appropriately. This page does not apply its former fixed trimester table or recommend medication from TSH alone. ATA thyroid function tests

Check with your maternity or thyroid team	Why it matters for this comparison
Is this the appropriate laboratory interval for my pregnancy?	The tool uses exactly what is entered
Is the result free T4 or total T4?	These cannot be substituted
Are the units the same as the interval?	Mixed units invalidate the comparison
Is there a separate clinical treatment target?	This tool does not choose that target

The ATA lists a 2026 preconception, pregnancy and postpartum guideline. The old 2017 table is not presented here as current universal guidance. The listing verifies the newer guideline's existence; it is not used to invent a treatment threshold without reading that recommendation. ATA current guideline directory

For other pregnancy tools, see our pregnancy weight gain calculator and due date calculator, each with its own scope and limitations.

Frequently Asked Questions

What is a normal TSH level?

Use the interval supplied for your laboratory test and clinical circumstances. This tool has no universal 0.4–4.0 range or 0.5–2.5 “optimal” target. A laboratory comparison is different from diagnosis or a personal treatment goal. ATA thyroid tests

What does a high TSH mean?

High TSH together with low free T4 suggests primary hypothyroidism. TSH alone cannot establish the full pattern or treatment. Discuss the report with your clinician rather than assigning “overt” disease from a single number. ATA interpretation

What does a low TSH mean?

It can occur with hyperthyroidism, but low TSH and low free T4 can occur with a pituitary cause of hypothyroidism. This tool reports separate interval comparisons and does not decide which explanation applies. ATA test patterns

Can thyroid problems cause weight gain?

Weight gain can be a symptom of hypothyroidism. That possibility does not establish a cause from weight change alone. The former pound ranges and cutoff for excluding thyroid disease are withheld because they were not adequately supported. ATA hypothyroidism symptoms

Sources

ATA: Thyroid Function Tests, test patterns and interpretation.
ATA: Hypothyroidism, symptoms and assessment.
ATA: Hyperthyroidism, symptoms and testing.
ATA guideline directory, 2026 pregnancy guideline listing. Sources accessed October 5, 2026. This is a source-based educational review, not practitioner review.