Thyroid in Primary Care: Symptoms, Labs, and How to Read Them (Fast)

A patient says they're tired, cold, and their hair is falling out. Or wired, losing weight, and not sleeping. Thyroid is on the list, but the symptoms are vague and you've got 15 minutes.

Here's a clinic-friendly way to triage the symptoms, order the right labs, and read the results fast.

What symptoms point to the thyroid?

None of these are specific, but a cluster should make you check a TSH:

• Fatigue or feeling wired and tired
• Heat or cold intolerance
• Skin or hair changes
• Constipation or diarrhea
• Anxiety or depression
• Menstrual irregularities or fertility concerns
• A feeling of fullness in the throat, painless enlargement, or voice changes
• Known goiter or nodule history

If you want the upstream picture of why these happen, see Thyroid Hormones 101.

What labs should I order?

Start here for most clinics:

• TSH with reflex to free T4. This is the efficient first move. You only pay for the free T4 if the TSH is abnormal.

If the patient asks for a "full panel":

• TSH, free T4, and a total or free T3. T3 mostly earns its place when TSH is suppressed and you're confirming hyperthyroidism, not for routine workups.

Antibodies, only when they change your plan:

• Order TPO when you're working up Hashimoto's or subclinical hypothyroidism (high TSH, normal free T4). A positive TPO raises the risk of progressing to overt hypothyroidism.
• Skip antibodies as routine screening in an asymptomatic, euthyroid patient.

One quick catch, biotin. Biotin supplements can falsely lower TSH and falsely raise T4 and T3. Have patients hold biotin for 48 hours before labs.

How do I read the results?

The core rule: TSH and thyroid hormone move in opposite directions. High TSH points to hypo. Low TSH points to hyper.

TSH normal

Reassure. No further testing unless there are strong clinical red flags.

TSH elevated

Add or confirm a free T4.

• High TSH plus low free T4 is overt hypothyroidism. Treat with levothyroxine.
• High TSH plus normal free T4 is subclinical hypothyroidism. Discuss it, recheck in about 3 months, and consider a TPO since positivity predicts progression. Treatment is reasonable when:
  • TSH is 10 mIU/L or higher, or
  • TSH is 4.5 to 9.9 with symptoms, goiter, positive TPO, pregnancy or pregnancy plans, or cardiovascular risk.

TSH low

Add free T4 and T3.

• Low TSH plus high free T4 or T3 is overt hyperthyroidism. Sort out Graves vs thyroiditis vs toxic nodule. Look for tremor, weight loss, tachycardia, and eye findings with Graves.
• Low TSH plus normal free T4 and T3 is subclinical hyperthyroidism. Repeat in 6 to 12 weeks. Treat if it persists in older adults, atrial fibrillation, or osteoporosis, or if TSH is under 0.1.

Don't miss these

• Central hypothyroidism. A low or normal TSH with a low free T4 points to the pituitary. Check other pituitary hormones and consider imaging.
• Non-thyroidal illness and meds. Severe illness, steroids, amiodarone, lithium, and biotin can all distort results. Read the labs in context.

When do I order imaging?

• Thyroid ultrasound for a palpable nodule, a goiter with local symptoms, or an abnormal exam. Not for lab abnormalities alone.
• Uptake scan (RAIU) when TSH is low and you need to tell Graves (diffuse uptake) from a toxic nodule (focal uptake) from thyroiditis (low uptake). Avoid if pregnant.

For nodule-specific next steps, see thyroid nodules in primary care.

Treatment starting points

• Overt hypothyroidism: levothyroxine around 1.6 mcg/kg/day in a healthy adult. Start lower in older adults or those with cardiovascular disease. Recheck TSH in 6 to 8 weeks and adjust by 12.5 to 25 mcg.
• Overt hyperthyroidism: a beta-blocker for symptoms while you work up the cause. Consider endocrinology for antithyroid meds (methimazole preferred), radioiodine, or surgery based on cause and patient factors.

The full treatment walk-throughs live in hypothyroidism treatment and hyperthyroidism first steps.

Pearls that save time

• Re-draw an abnormal screen before you label a diagnosis. Confirming rules out biotin and illness effects.
• TSH lags after a dose change. Wait 6 to 8 weeks to recheck after adjusting levothyroxine.
• For a symptomatic hyperthyroid patient, start a beta-blocker while you sort the cause.
• Positive TPO with subclinical hypo? Patients appreciate a shared-decision talk about treating early vs watchful waiting.

Frequently asked questions

Do I need a free T3 on every thyroid workup?
No. T3 mainly helps when TSH is suppressed and you're confirming hyperthyroidism. For routine cases, TSH with reflex free T4 is enough.

When can I treat subclinical hypothyroidism?
It's reasonable when TSH is 10 or higher, or 4.5 to 9.9 with symptoms, goiter, positive TPO, pregnancy or plans, or cardiovascular risk.

Why is my patient's TSH off if they feel fine?
Check biotin use, recent illness, and timing after a dose change. Re-draw before committing to a diagnosis.

How soon do I recheck after starting or changing levothyroxine?
In 6 to 8 weeks. TSH lags behind dose changes, so earlier rechecks just confuse the picture.

Want this on one page at your desk? The Clinical Desk Reference puts the thyroid lab logic in a $37 quick-reference. For the full system on working through any visit, the Primary Care Clinical Mastery Program is AANP-accredited.

Education only. Use clinical judgment and your local guidelines.

Written by Allison Sowders, MSN, APRN, FNP-BC, a practicing primary care nurse practitioner and founder of Nurse Practitioner Mentor. Reviewed July 2026.