The thyroid gland makes thyroxine (T4) and triiodothyronine (T3), which set the body's metabolic rate, heat production, heart rate, and gut motility. Production is controlled by a feedback loop: hypothalamic TRH → pituitary TSH → thyroid hormone, which then suppresses TSH. Iodine is required to make thyroid hormone.
The four parathyroid glands, behind the thyroid, secrete parathyroid hormone (PTH), which raises serum calcium (bone release, kidney calcium reabsorption, activation of vitamin D) and lowers serum phosphorus (increases kidney phosphate excretion). Calcium and phosphorus move in opposite directions.
| Feature | Hyperthyroidism | Hypothyroidism |
|---|
| Most common cause | Graves disease (autoimmune antibodies stimulate the TSH receptor) — the most common cause; also toxic nodular goiter, thyroiditis | Hashimoto (autoimmune) thyroiditis where iodine is sufficient; iodine deficiency worldwide; after thyroidectomy or radioactive iodine |
| Metabolism | Increased | Decreased |
| Temperature | Heat intolerance, sweating | Cold intolerance |
| Weight | Weight loss despite increased appetite | Weight gain, poor appetite |
| Heart | Tachycardia, palpitations, atrial fibrillation, systolic hypertension | Bradycardia, low voltage ECG, pericardial effusion |
| Bowel | Frequent stools, diarrhea | Constipation |
| Neuro/mood | Nervousness, tremor, insomnia, hyperreflexia | Fatigue, slowed thinking, depression, slow reflexes |
| Skin/hair | Warm, moist skin; fine hair | Dry coarse skin, hair loss, puffy face, nonpitting edema |
| Menses | Light or absent | Heavy |
| Unique | Exophthalmos, lid lag, goiter, pretibial myxedema (Graves) | Hoarse voice, hyperlipidemia |
Thyroid nodules are common; most are benign. Evaluation uses TSH, ultrasound, and fine-needle aspiration (FNA).
Graves ophthalmopathy — protruding eyes, eyelid retraction, gritty dry eyes, tearing, light sensitivity, double vision; severe cases risk corneal ulceration or optic nerve compression (color vision loss).
Hyperparathyroidism — often found by routine calcium testing; symptoms summarized as "stones, bones, abdominal groans, and psychic moans":
- Kidney stones, polyuria
- Bone pain, osteoporosis, fractures
- Constipation, nausea, peptic ulcer, pancreatitis
- Fatigue, weakness, depression, confusion
- Shortened QT interval
Hypoparathyroidism / hypocalcemia — most often after thyroid or parathyroid surgery:
- Numbness and tingling around the mouth, fingers, and toes; muscle cramps
- Chvostek sign (tapping the facial nerve in front of the ear → facial twitch)
- Trousseau sign (BP cuff inflated above systolic for up to 3 minutes → carpal spasm)
- Tetany, laryngospasm (stridor), seizures; prolonged QT interval
| Condition | TSH | Free T4 |
|---|
| Primary hyperthyroidism | Low | High |
| Primary hypothyroidism | High | Low |
| Subclinical hypothyroidism | High | Normal |
| Secondary (pituitary) hypothyroidism | Low or normal | Low |
- TSH is the best screening test (typical adult reference about 0.4–4.0 mIU/L; laboratory ranges vary)
- TSH receptor antibodies (TRAb/TSI) confirm Graves disease; anti-TPO antibodies support Hashimoto thyroiditis
- Radioactive iodine uptake scan — diffuse high uptake (Graves), "hot" nodule, low uptake (thyroiditis); contraindicated in pregnancy and breastfeeding
- Thyroid ultrasound and FNA for nodules. Results use the Bethesda categories. An "atypia of undetermined significance" result is indeterminate — the usual next step is repeat FNA and/or molecular testing (sometimes diagnostic surgery), not treatment
- Calcium: total serum calcium about 8.5–10.5 mg/dL (2.12–2.62 mmol/L); correct for low albumin or measure ionized calcium
- Hyperparathyroidism: high calcium, high or inappropriately normal PTH, low phosphorus
- Hypoparathyroidism: low calcium, low PTH, high phosphorus; check magnesium (low magnesium impairs PTH release)
Hyperthyroidism
- Beta blockers (propranolol, atenolol) for tachycardia, tremor, and anxiety — hold for bradycardia or hypotension; caution with asthma
- Antithyroid drugs (thionamides)
- Methimazole — preferred for most clients
- Propylthiouracil (PTU) — boxed warning for severe liver injury; used mainly in the first trimester of pregnancy (methimazole can cause birth defects then; clients are usually switched to methimazole after the first trimester) and in thyroid storm
- Both can cause agranulocytosis — stop the drug and report fever, sore throat, or mouth sores immediately (check CBC); also rash, liver injury, vasculitis
- Radioactive iodine (I-131) — destroys thyroid tissue over weeks to months; pregnancy must be excluded and avoided for about 6 months after; most clients later develop hypothyroidism needing lifelong levothyroxine; may worsen Graves eye disease (steroid cover may be given)
- Thyroidectomy — for large goiter, suspected cancer, severe eye disease, pregnancy intolerant of drugs. Before surgery, clients should be euthyroid; iodine solutions (potassium iodide, Lugol solution) may be given for about 10 days to reduce gland vascularity — dilute in juice, drink through a straw (staining)
Hypothyroidism
- Levothyroxine (synthetic T4), lifelong
- Take on an empty stomach, 30–60 minutes before breakfast (or at bedtime, 3 hours after the last meal), with water, the same way every day
- Separate by about 4 hours from calcium, iron, antacids, and bile-acid binders
- Start low and go slow in older adults and clients with heart disease (can trigger angina or arrhythmia)
- Signs of excess dose: palpitations, tachycardia, insomnia, weight loss, heat intolerance
- Boxed warning: not for weight loss
- Raises warfarin effect as the client becomes euthyroid — monitor INR
- TSH is rechecked about 6–8 weeks after a dose change
- Pregnancy: requirements rise early — many clients need about a 20–30% dose increase as soon as pregnancy is confirmed; TSH is kept in a lower, trimester-specific range (commonly < 2.5 mIU/L); levothyroxine is safe in pregnancy and breastfeeding and must not be stopped
- Myxedema coma (severe decompensated hypothyroidism): IV levothyroxine, IV hydrocortisone until adrenal insufficiency is excluded, ventilatory support, passive rewarming, cautious fluids for hyponatremia; avoid sedatives
Hyperparathyroidism
- Parathyroidectomy — definitive for symptomatic disease and for those meeting surgical criteria
- Hydration (IV normal saline for severe hypercalcemia) then loop diuretics if volume-overloaded; avoid thiazide diuretics (raise calcium)
- Cinacalcet (calcimimetic) — hypocalcemia, nausea; calcitonin for rapid short-term lowering; bisphosphonates or denosumab for bone protection or severe hypercalcemia (hypocalcemia, osteonecrosis of the jaw; check creatinine before zoledronic acid)
Hypoparathyroidism
- Acute tetany: IV calcium gluconate — the first-line emergency drug; give slowly with cardiac monitoring; watch for extravasation (tissue necrosis) and bradycardia; dangerous with digoxin (arrhythmia); do not mix with bicarbonate or phosphate
- Chronic: oral calcium plus active vitamin D (calcitriol); correct low magnesium; PTH replacement in selected clients
Listed in priority order.
- After thyroidectomy — airway first
- Watch for bleeding/hematoma (neck swelling, tight dressing, check the back of the neck and pillow for blood), stridor, and respiratory distress; an expanding neck hematoma with airway compromise is an emergency — call the surgeon or rapid response team; the wound may need to be opened at the bedside per protocol
- Keep tracheostomy tray, suction, and oxygen at the bedside; semi-Fowler position; support the head and neck (avoid neck hyperextension)
- Recurrent laryngeal nerve injury — assess voice every few hours; mild hoarseness is common; bilateral injury can cause airway obstruction
- Hypocalcemia usually appears within 24–72 hours — ask about tingling, check Chvostek and Trousseau signs, monitor calcium; keep IV calcium gluconate available; seizure precautions
- Thyroid storm (thyrotoxic crisis) — high fever (often > 38.5°C (101.3°F)), severe tachycardia or atrial fibrillation, agitation, delirium, vomiting; triggered by infection, surgery, stopping medication, or RAI. Give thionamide (PTU or methimazole) first, then iodine at least 1 hour later, beta blocker, corticosteroid, cooling (cooling blankets, acetaminophen — not aspirin, which frees thyroid hormone), fluids, cardiac monitoring
- Hypothyroid safety — monitor for bradycardia, hypothermia, and hypoventilation; use sedatives and opioids cautiously (slowed metabolism — risk of myxedema coma)
- Eye protection (Graves) — artificial tears frequently, sunglasses, elevate head of bed to reduce periorbital edema, tape or shield eyelids at night if they do not close, report vision change; smoking cessation
- Hyperthyroid comfort and nutrition — cool, quiet environment; high-calorie, high-protein diet with frequent meals; avoid caffeine; rest periods
- Hypothyroid comfort — warm environment and extra blankets (no heating pads — reduced sensation and vasodilation), fiber and fluids for constipation, low-calorie diet
- Hyperparathyroidism — encourage fluids (about 2–3 L/day unless restricted) to prevent stones; strain urine as needed; fall and fracture precautions; ambulation (immobility raises calcium)
- Levothyroxine: lifelong; empty stomach with water 30–60 minutes before breakfast; separate from calcium and iron; do not switch brands without checking; do not stop in pregnancy; report palpitations or chest pain
- Antithyroid drugs: take as prescribed and never adjust the dose alone; report fever, sore throat, or mouth ulcers at once (agranulocytosis); report yellow skin, dark urine, or right upper abdominal pain (liver injury)
- Radioactive iodine precautions (per program instructions, usually for several days): avoid close and prolonged contact with pregnant women and young children, sleep alone, keep distance from others, do not share utensils, flush the toilet twice and sit to void, wash hands well, drink fluids; avoid pregnancy for about 6 months; watch for symptoms of hypothyroidism later
- After thyroidectomy: gentle neck range of motion as healing allows; report tingling or cramps immediately; lifelong levothyroxine after total thyroidectomy
- Hyperparathyroidism: adequate fluids, stay active, avoid thiazides and excess vitamin D or calcium supplements unless prescribed
- Hypoparathyroidism: take calcium and calcitriol as prescribed; know signs of low and high calcium; medical alert identification
- Thyroid storm — life-threatening hypermetabolic crisis
- Myxedema coma — hypothermia, bradycardia, hypoventilation, hyponatremia, stupor
- Post-thyroidectomy airway obstruction — hematoma, laryngeal edema, bilateral vocal cord paralysis
- Hypocalcemic tetany — laryngospasm, seizures, arrhythmia
- Agranulocytosis and severe liver injury from thionamides
- Hypercalcemic crisis — dehydration, confusion, arrhythmia
- Atrial fibrillation and heart failure in untreated hyperthyroidism; vision loss in severe eye disease
- Graves disease is the most common cause of hyperthyroidism; low TSH, high free T4
- Hypothyroidism: high TSH, low free T4 — fatigue, cold intolerance, constipation, weight gain, bradycardia
- Levothyroxine on an empty stomach, separate from calcium and iron; start low in older adults and heart disease; increase dose in pregnancy — never stop
- Methimazole/PTU: report fever and sore throat (agranulocytosis); PTU → liver injury, used in first trimester and thyroid storm
- RAI: exclude pregnancy; limit close contact with pregnant women and young children; later hypothyroidism
- After thyroidectomy: airway and bleeding first; trach set at bedside; check behind the neck; hypocalcemia (tingling, Chvostek, Trousseau) → IV calcium gluconate
- Graves eyes: artificial tears, sunglasses, HOB up, tape lids at night
- Thyroid storm: thionamide → iodine 1 h later → beta blocker, steroid; acetaminophen, not aspirin
- Hyperparathyroidism: high calcium, low phosphorus — stones, bones, groans; fluids, mobility; avoid thiazides
- Hypoparathyroidism: low calcium, high phosphorus
- Indeterminate FNA (atypia of undetermined significance): repeat FNA or molecular testing
Country Notes
United States
- Free T4 is reported in ng/dL (about 0.8–1.8 ng/dL; lab-specific) and calcium in mg/dL.
- Iodine deficiency is uncommon because of iodized salt, so autoimmune thyroiditis dominates as the cause of hypothyroidism.
Philippines
- Free T4 is often reported in pmol/L (1 ng/dL ≈ 12.9 pmol/L) and calcium in mmol/L — check units.
- Salt iodization is required by law (the ASIN law, Republic Act 8172); iodine deficiency goiter persists in some inland and upland areas — encourage use of iodized salt, while clients on radioactive iodine or with hyperthyroidism follow their provider's specific iodine advice.
- Radioactive iodine therapy is available mainly in larger hospitals with nuclear medicine units; teach home radiation precautions carefully because households are often crowded and multigenerational.