One-liner#

Recognize hypothyroidism presenting as fatigue, weight gain, cold intolerance, or constipation; confirm with TSH/free T4; initiate levothyroxine with appropriate dosing based on age and cardiac status.

Quick nav#

• Red flags / send to ED
• Key history
• Focused exam
• Differential (quick pattern recognition)
• Workup
• Initial management
• Management by diagnosis
• Follow-up
• Patient instructions
• Smartphrase snippets

Red flags / send to ED#

• Myxedema coma: Altered mental status + hypothermia + bradycardia + hypotension in setting of severe hypothyroidism → call 911
• Severe symptomatic bradycardia (HR <40 with syncope, hypotension) → ED
• Severe hyponatremia (Na <120 or symptomatic) → ED
• Respiratory failure (CO2 retention, severe hypoxia) → ED
• Adrenal crisis (if concurrent adrenal insufficiency—hypotension, shock) → ED

Myxedema coma triggers: Infection, cold exposure, sedatives/opioids, surgery, trauma, medication non-adherence

Key history#

Classic hypothyroid symptoms:

• Fatigue, low energy, feeling “slowed down”
• Weight gain (usually modest, 5-10 lbs)
• Cold intolerance
• Constipation
• Dry skin, brittle nails
• Hair loss, thinning hair
• Muscle aches, cramps, weakness
• Joint pain, stiffness

Cognitive/mood symptoms:

• Depression, low mood
• Difficulty concentrating, “brain fog”
• Memory problems
• Slowed thinking

Cardiovascular:

• Bradycardia
• Dyspnea on exertion
• Edema (non-pitting, myxedematous)

Reproductive:

• Menstrual irregularities (menorrhagia, oligomenorrhea)
• Infertility
• Decreased libido
• Erectile dysfunction

Other:

• Hoarseness
• Hearing loss
• Carpal tunnel symptoms
• Sleep apnea symptoms

Timeline and course:

• Onset: usually gradual (months to years)
• Prior thyroid disease or treatment (RAI, surgery, radiation)
• Recent pregnancy (postpartum thyroiditis)
• Recent medication changes

Medication review:

• Amiodarone (can cause hypo- or hyperthyroidism)
• Lithium (common cause of hypothyroidism)
• Interferon-alpha, IL-2
• Tyrosine kinase inhibitors
• Checkpoint inhibitors (immunotherapy)
• Iodine excess

Past medical history:

• Prior thyroid surgery or RAI
• Head/neck radiation
• Autoimmune diseases (type 1 DM, celiac, vitiligo, pernicious anemia)
• Down syndrome, Turner syndrome

Family history:

• Thyroid disease
• Autoimmune conditions

Focused exam#

Vital signs:

• Bradycardia
• Diastolic hypertension (narrowed pulse pressure)
• Hypothermia (severe cases)

General:

• Slow movements, slow speech
• Dull facial expression
• Periorbital puffiness
• Weight gain

Skin/hair/nails:

• Dry, coarse, cool skin
• Non-pitting edema (myxedema)—hands, face, pretibial
• Coarse, brittle hair
• Lateral eyebrow thinning (Queen Anne sign)
• Brittle, ridged nails
• Yellowish skin (carotenemia)

Thyroid exam:

• Size: may be enlarged (Hashimoto’s) or atrophic
• Texture: firm, rubbery (Hashimoto’s)
• Nodules: note if present
• Surgical scar: prior thyroidectomy

Cardiovascular:

• Bradycardia
• Distant heart sounds (if pericardial effusion)
• Peripheral edema

Neurologic:

• Delayed relaxation phase of deep tendon reflexes (“hung-up” reflexes)
• Carpal tunnel signs (Tinel’s, Phalen’s)
• Proximal muscle weakness
• Cerebellar signs (ataxia—severe cases)

Mental status:

• Slowed cognition
• Depression
• Confusion (severe cases)

Differential (quick pattern recognition)#

Common/likely (outpatient)#

Can’t-miss / urgent#

Workup#

Initial labs (all suspected hypothyroidism):

Second-tier labs:

When to suspect central hypothyroidism:

• Low or inappropriately normal TSH with low free T4
• Other pituitary hormone deficiencies
• History of pituitary surgery, radiation, or tumor
• Headaches, visual field defects

If central hypothyroidism suspected:

• Do NOT rely on TSH for monitoring
• Check cortisol before starting levothyroxine (can precipitate adrenal crisis)
• MRI pituitary
• Refer to endocrinology

Other tests to consider:

When NOT to order:

• TPO antibodies if already planning to treat (doesn’t change management)
• Free T3 for routine diagnosis or monitoring
• Thyroid ultrasound unless nodule palpated or goiter asymmetric
• Repeat TSH within 6 weeks of dose change (takes time to equilibrate)

Biotin interference: Biotin supplements can cause falsely normal/low TSH and falsely low free T4. Ask about supplements; hold biotin for 2-3 days before labs.

Initial management#

Who to treat:

• Overt hypothyroidism (elevated TSH + low free T4): always treat
• Subclinical hypothyroidism: treat based on TSH level, symptoms, and risk factors (see below)

Levothyroxine dosing principles:

• Full replacement: ~1.6 mcg/kg/day (lean body weight)
• Most adults: 50-100 mcg daily starting dose
• Elderly or cardiac disease: start low (12.5-25 mcg), increase slowly
• Severe/longstanding hypothyroidism: start low, increase gradually

Levothyroxine administration:

• Take on empty stomach, 30-60 minutes before breakfast
• OR at bedtime, 3+ hours after last meal
• Separate from calcium, iron, PPIs, antacids by 4 hours
• Consistency is key—same time, same way daily

Management by diagnosis#

Overt primary hypothyroidism (Hashimoto’s)#

Education:

• Autoimmune condition; immune system attacks thyroid
• Lifelong treatment usually required
• Medication replaces what thyroid can’t make
• Takes 4-6 weeks to feel full effect of dose changes
• Many symptoms will improve with treatment

Treatment:

TSH targets:

• Most adults: 0.5-2.5 mIU/L (lower half of normal range)
• Elderly (>70): 1-5 mIU/L acceptable (avoid overtreatment)
• Pregnancy: trimester-specific (see below)

Common reasons for persistent elevated TSH despite treatment:

1. Non-adherence (most common)
2. Incorrect administration (with food, calcium, iron, coffee)
3. Malabsorption (celiac, gastric bypass, IBD)
4. Drug interactions (PPIs, bile acid sequestrants, sucralfate)
5. Inadequate dose
6. Generic substitution issues (rare)

If TSH remains elevated despite adequate dose:

• Confirm adherence and proper administration
• Check for malabsorption (celiac serology if suspected)
• Review medications for interactions
• Consider increasing dose or switching to brand-name

Follow-up: TSH 6-8 weeks after starting or dose change; once stable, annually.

What about T3 (liothyronine) or combination T4/T3 therapy?

Patients often ask about adding T3 or using desiccated thyroid (Armour Thyroid). Current evidence:

• Most guidelines recommend levothyroxine monotherapy as standard of care
• Randomized trials show no consistent benefit of combination T4/T3 over T4 alone
• Desiccated thyroid has inconsistent T3:T4 ratios and is not recommended by major guidelines
• Some patients report subjective improvement on combination therapy despite normal TSH

PCP approach:

• First, optimize levothyroxine (adherence, administration, dose)
• If persistent symptoms despite normal TSH: evaluate for other causes (depression, sleep apnea, anemia, etc.)
• If patient strongly prefers trial of combination therapy: refer to endocrinology
• Do NOT start liothyronine in primary care—short half-life requires careful dosing and monitoring

Subclinical hypothyroidism#

Definition: Elevated TSH (4.5-10 mIU/L) with normal free T4

Who to treat:

• TSH >10 mIU/L: treat (high progression rate to overt hypothyroidism)
• TSH 4.5-10 mIU/L with symptoms: consider treatment trial
• TSH 4.5-10 mIU/L with positive TPO antibodies: consider treatment (higher progression risk)
• Pregnancy or planning pregnancy: treat (see below)
• Goiter: consider treatment

Who to observe:

• TSH 4.5-10 mIU/L, asymptomatic, TPO negative
• Elderly (>70): higher TSH may be normal; avoid overtreatment

If treating: Start levothyroxine 25-50 mcg daily; titrate to TSH goal.

If observing: Repeat TSH in 6-12 months; sooner if symptoms develop.

Hypothyroidism in pregnancy#

Why it matters:

• Untreated hypothyroidism increases risk of miscarriage, preterm birth, preeclampsia, impaired fetal neurodevelopment
• Thyroid hormone requirements increase 25-50% in pregnancy

TSH goals in pregnancy:

• 1st trimester: <2.5 mIU/L
• 2nd trimester: <3.0 mIU/L
• 3rd trimester: <3.5 mIU/L

Management:

• If on levothyroxine pre-pregnancy: increase dose by ~30% as soon as pregnancy confirmed (or add 2 extra doses per week)
• Check TSH every 4 weeks in 1st trimester, then every 4-6 weeks
• Refer to endocrinology or MFM for co-management

Subclinical hypothyroidism in pregnancy:

• TSH >4.0 with positive TPO antibodies: treat
• TSH >10: treat regardless of TPO status
• TSH 2.5-4.0 with positive TPO: consider treatment

Postpartum:

• Reduce dose to pre-pregnancy level after delivery
• Check TSH 6 weeks postpartum

Central hypothyroidism#

Key differences:

• TSH is unreliable (may be low, normal, or slightly elevated)
• Monitor free T4, not TSH
• Must rule out adrenal insufficiency before starting levothyroxine

PCP role:

• Recognize (low free T4 with inappropriately normal/low TSH)
• Check morning cortisol before starting levothyroxine
• Refer to endocrinology

Drug-induced hypothyroidism#

Common culprits:

• Amiodarone: check TSH every 6 months while on drug
• Lithium: check TSH every 6-12 months
• Checkpoint inhibitors: can cause thyroiditis → hypothyroidism

Management:

• If drug can be stopped: may recover thyroid function
• If drug must continue: treat with levothyroxine as usual
• Amiodarone-induced: often requires ongoing levothyroxine even after stopping amiodarone

Follow-up#

After starting levothyroxine:

• TSH in 6-8 weeks
• Adjust dose by 12.5-25 mcg based on TSH
• Repeat TSH 6-8 weeks after each dose change

Once stable:

• TSH annually
• Sooner if symptoms change or pregnancy

Subclinical hypothyroidism (observing):

• TSH every 6-12 months
• Sooner if symptoms develop

Return precautions:

• Chest pain, palpitations, shortness of breath (overtreatment or cardiac disease)
• Symptoms not improving after 2-3 months of treatment
• New symptoms suggesting overtreatment (anxiety, tremor, weight loss, insomnia)
• Pregnancy (need dose adjustment)

Patient instructions#

• Your thyroid gland is underactive and not making enough thyroid hormone. This slows down your body’s metabolism.
• Levothyroxine replaces the hormone your thyroid can’t make. You will likely need to take it for life.
• Take your medication on an empty stomach, at least 30-60 minutes before eating. Many people take it first thing in the morning.
• Do not take levothyroxine at the same time as calcium, iron supplements, or antacids—wait at least 4 hours.
• It takes 4-6 weeks to feel the full effect of a dose change. Be patient.
• Do not stop taking your medication even if you feel better. Your symptoms will return.
• We will check your thyroid level (TSH) periodically to make sure your dose is correct.
• Call us if you develop chest pain, racing heart, or feel jittery—this could mean your dose is too high.
• If you become pregnant or are planning pregnancy, let us know right away—your dose will need to be adjusted.

Smartphrase snippets#

.HYPOTHYROIDNEW Patient presents with symptoms consistent with hypothyroidism including [fatigue/weight gain/cold intolerance/constipation]. TSH [value] (elevated), free T4 [value] (low/normal). Diagnosis: [overt hypothyroidism/subclinical hypothyroidism]. Starting levothyroxine [dose] daily. Counseled on proper administration (empty stomach, separate from calcium/iron). Will recheck TSH in 6-8 weeks. Patient instructed to report chest pain, palpitations, or worsening symptoms.

.HYPOTHYROIDFOLLOWUP Hypothyroidism follow-up. Current dose: levothyroxine [dose]. Symptoms: [improved/stable/persistent]. TSH today: [value] (goal 0.5-2.5). [At goal/above goal/below goal]. Plan: [continue current dose/increase to X mcg/decrease to X mcg]. Recheck TSH in [6-8 weeks if dose change/annually if stable]. Proper administration and adherence reviewed.

.SUBCLINICALHYPO Incidental finding of elevated TSH [value] with normal free T4 [value] consistent with subclinical hypothyroidism. Patient is [asymptomatic/symptomatic with fatigue, etc.]. TPO antibodies [positive/negative/not checked]. Risk factors for progression: [TPO positive/goiter/none]. Plan: [Repeat TSH in 6-8 weeks to confirm / Start levothyroxine 25-50 mcg given symptoms and TPO positivity / Observe with TSH every 6-12 months]. Patient advised to report fatigue, weight gain, or other hypothyroid symptoms.

.HYPOTHYROIDPREGNANCY Patient with hypothyroidism, now pregnant at [X] weeks. Pre-pregnancy levothyroxine dose: [X mcg]. Increased dose to [X mcg] (approximately 30% increase). TSH today: [value] (goal <2.5 in 1st trimester). Plan: Recheck TSH in 4 weeks. Continue prenatal vitamins (take separately from levothyroxine). Will coordinate with OB/endocrinology as needed.

Related pages#

• Hypothyroidism (problem) — comprehensive ongoing management of hypothyroidism including dosing, monitoring, and special populations
• Fatigue — hypothyroidism as cause
• Weight gain — hypothyroidism as cause
• Depression — can mimic or coexist
• Hyperthyroid — opposite presentation
• Constipation — hypothyroidism as cause
• Hyperlipidemia (problem) — hypothyroidism causes secondary hyperlipidemia

Coding/billing notes#

• E03.9: Hypothyroidism, unspecified
• E06.3: Autoimmune thyroiditis (Hashimoto’s)
• E03.2: Hypothyroidism due to medications and other exogenous substances
• E89.0: Postprocedural hypothyroidism
• E02: Subclinical iodine-deficiency hypothyroidism
• O99.280: Endocrine, nutritional and metabolic diseases complicating pregnancy