Thyroid and sex hormone markers

Why it matters: USPSTF finds insufficient evidence to screen adults without symptoms, so we test when there's a reason.

Ranges: Your lab's range applies (often about 0.4–4.0 mIU/L).

What can affect it: Illness, biotin supplements, pregnancy and thyroid medicines.

If it’s out of range: Abnormal results are confirmed before any treatment.

When to retest: 6–8 weeks after a thyroid medicine change.

Condition guide: Underactive thyroid care online · Overactive thyroid care online

Why it matters: Added when TSH is abnormal to show how the thyroid is working.

Ranges: Your lab's range applies.

What can affect it: Biotin, illness and thyroid medicines.

If it’s out of range: Read with TSH.

When to retest: With TSH.

Condition guide: Underactive thyroid care online · Overactive thyroid care online

Why it matters: The Endocrine Society recommends diagnosing low testosterone only with symptoms and consistently low morning levels.

Ranges: Your lab's range applies (a commonly used adult male range is about 264–916 ng/dL).

What can affect it: Time of day, sleep, weight, illness and opioids.

If it’s out of range: A low result is confirmed with a second morning test before any treatment.

When to retest: A second morning test to confirm.

Condition guide: Low testosterone test guide

Why it matters: Used to calculate free testosterone.

Ranges: Your lab's range applies.

What can affect it: Age, weight, thyroid and liver conditions.

If it’s out of range: Read with total testosterone.

When to retest: With testosterone.

Condition guide: Low testosterone test guide

Why it matters: Calculated from total testosterone, SHBG and albumin, which guidelines prefer over direct tests.

Ranges: Your lab's range applies.

What can affect it: Same as total testosterone and SHBG.

If it’s out of range: Shown, not counted.

When to retest: With testosterone.

Condition guide: Low testosterone test guide

Why it matters: Helpful in selected women's and men's health questions.

Ranges: Varies with the menstrual cycle and menopause.

What can affect it: Cycle timing, hormone therapy and weight.

If it’s out of range: Read with symptoms and FSH.

When to retest: As advised.

Condition guide: Perimenopause care online · Menopause care online

Why it matters: Menopause after 45 is usually diagnosed from symptoms; FSH helps when periods change earlier or the picture is unclear.

Ranges: Varies with the menstrual cycle.

What can affect it: Cycle timing and hormonal birth control.

If it’s out of range: Read with symptoms and estradiol.

When to retest: As advised.

Condition guide: Perimenopause care online · Menopause care online

Why it matters: USPSTF recommends an individual decision about PSA screening for men 55–69 after discussing benefits and harms.

Ranges: Interpreted with age and prior results.

What can affect it: Prostate size, infection, recent ejaculation and cycling.

If it’s out of range: An elevated result is repeated and discussed before any referral.

When to retest: As agreed with your clinician.

Condition guide: Prostate cancer screening online