Heart Palpitations — Blood Tests to Find the Cause
Most palpitations are not dangerous — but they often have a treatable cause that a simple blood test can identify. Here is what to ask your GP for.
Quick Summary — What to Ask Your GP
Heart palpitations — the awareness of your own heartbeat as racing, pounding, fluttering, or skipping — are usually benign but always worth investigating. The five most common medical causes are hyperthyroidism, anaemia, low potassium or magnesium, dehydration, and reactive low blood sugar. Anxiety and caffeine are common contributors but should be diagnoses of exclusion.
Ask your GP for: TSH and free T4 (thyroid), full blood count, ferritin, electrolytes (sodium, potassium, magnesium, calcium), kidney function, fasting glucose and HbA1c, vitamin B12, and a lipid profile. An ECG and 24-hour Holter monitor will often be ordered alongside.
Once you have results, upload them to SmarterBlood for a free, plain-language explanation of every marker relevant to heart rhythm and circulation.
8 Causes of Heart Palpitations Your Blood Can Reveal
Hyperthyroidism (Overactive Thyroid)
How it causes palpitations: Thyroid hormones directly increase heart rate, contractility, and the sensitivity of the heart muscle to adrenaline. When thyroid hormone levels are too high (hyperthyroidism), the heart beats faster and more forcefully at rest, and arrhythmias such as atrial fibrillation become much more likely. The hallmark blood pattern is a suppressed TSH (often below 0.1 mIU/L) with elevated free T4 or T3. Graves disease (autoimmune) is the most common cause in Australian adults under 60; toxic nodular goitre becomes more common after 60.
Typical pattern:
A racing or pounding heart at rest, often with weight loss despite a normal or increased appetite, heat intolerance, sweating, tremor of the hands, anxiety, irritability, loose stools, and difficulty sleeping. Some people notice bulging eyes (Graves ophthalmopathy) or a swollen neck (goitre).
What to do next: Ask your GP for TSH and free T4 (and free T3 if available). If TSH is suppressed, your GP will check thyroid antibodies and refer you to an endocrinologist. Beta-blockers are typically used for symptom control, with anti-thyroid medications, radioactive iodine, or surgery as definitive treatment options.
Anaemia (Iron Deficiency or Other)
How it causes palpitations: Anaemia means reduced oxygen-carrying capacity of the blood. To deliver enough oxygen to the tissues, the heart has to compensate by beating faster and harder. This produces a sensation of palpitations, especially with exertion or when standing up. Iron deficiency is the most common cause in pre-menopausal women due to menstrual blood loss. B12 and folate deficiencies can also cause anaemia, and chronic disease, kidney failure, or bone marrow problems may contribute in older adults.
Typical pattern:
Palpitations on exertion or after standing up, often with fatigue, breathlessness on stairs, pale skin, brittle nails, hair shedding, and craving ice (pagophagia, classic for iron deficiency). May be present at rest if anaemia is severe.
What to do next: Ask for a full blood count (haemoglobin and red cell indices), ferritin, iron studies, vitamin B12, and folate. If anaemia is confirmed, treatment depends on the cause: oral iron or iron infusion for iron deficiency, B12 injections for B12 deficiency, and investigation for blood loss in any unexplained iron deficiency in men or postmenopausal women.
Electrolyte Imbalance
How it causes palpitations: The heart muscle is exquisitely sensitive to electrolyte concentrations because every heartbeat depends on the movement of potassium, sodium, calcium, and magnesium ions across cell membranes. Low potassium (hypokalaemia, often under 3.5 mmol/L) and low magnesium (hypomagnesaemia, often under 0.7 mmol/L) are the classic culprits. Causes include diuretics, vomiting, diarrhoea, eating disorders, alcohol use, and chronic kidney disease. Both can cause dangerous arrhythmias such as torsades de pointes.
Typical pattern:
Palpitations plus muscle cramps, weakness, fatigue, constipation, and sometimes a tingling sensation around the mouth or in the fingers (low calcium). May be triggered by recent illness with vomiting or diarrhoea, starting a new diuretic, or heavy alcohol use.
What to do next: Ask for an electrolyte panel including sodium, potassium, magnesium, and calcium (corrected for albumin). Mild deficiencies can be corrected with diet and oral supplements; severe deficiencies need IV replacement and continuous heart monitoring. The underlying cause must be identified and addressed.
Dehydration
How it causes palpitations: Dehydration reduces circulating blood volume. To maintain blood pressure and oxygen delivery, the heart compensates by beating faster (compensatory tachycardia). Blood becomes more concentrated, which raises haematocrit, urea-to-creatinine ratio, and sodium. Dehydration is common in hot Australian summers, with heavy exercise, with gastroenteritis, in older adults who do not feel thirsty, and with diuretic use.
Typical pattern:
Palpitations with dry mouth, dark concentrated urine, dizziness on standing, fatigue, headache, and reduced urine output. Skin may feel dry. Often improves rapidly with rehydration.
What to do next: Mild dehydration responds to oral rehydration with water and electrolyte solutions. Severe dehydration (especially in older adults, infants, or with persistent vomiting) needs IV fluids in hospital. A standard biochemistry panel will confirm dehydration via raised urea and creatinine ratio, raised sodium, and concentrated urine.
Hypoglycaemia (Low Blood Sugar)
How it causes palpitations: When blood glucose drops below about 3.9 mmol/L, the body releases adrenaline to mobilise glucose stores. This adrenaline surge produces palpitations, sweating, tremor, and anxiety; the symptoms resolve when glucose is restored. In people without diabetes, reactive hypoglycaemia (a sharp drop in blood sugar a few hours after a high-carbohydrate meal) is the most common cause. In people with diabetes, palpitations can be a warning sign of medication-related hypoglycaemia.
Typical pattern:
Palpitations 2 to 4 hours after a meal (especially carbohydrate-heavy), often with sweating, tremor, hunger, anxiety, and brain fog. Resolves with eating. Diabetics on insulin or sulfonylureas may also experience palpitations from low glucose.
What to do next: Ask for fasting glucose and HbA1c. If reactive hypoglycaemia is suspected, your GP may organise a 75-gram oral glucose tolerance test with extended sampling. Dietary changes (smaller, more frequent meals; reducing refined carbohydrates; pairing carbs with protein and fat) usually help.
Phaeochromocytoma (Rare)
How it causes palpitations: Phaeochromocytoma is a rare adrenal gland tumour that secretes excess adrenaline and noradrenaline. The result is episodes of severe palpitations, headache, sweating, and dramatic rises in blood pressure. Although rare (about 1 case per 100,000 per year), it is important to consider in anyone with palpitations plus paroxysmal hypertension, especially if young or with a family history of phaeochromocytoma or related syndromes.
Typical pattern:
Episodic spells of pounding palpitations, severe headache, profuse sweating, and very high blood pressure that come on suddenly and last 15 to 60 minutes. Between episodes, blood pressure may be normal or only mildly elevated. Episodes can be triggered by exercise, certain foods, or stress.
What to do next: Ask your GP for plasma metanephrines or 24-hour urinary metanephrines and catecholamines. These are the gold-standard screening tests. A positive screen will lead to endocrinology referral and CT or MRI imaging of the adrenals.
Caffeine, Alcohol and Stimulants
How it causes palpitations: Caffeine, alcohol (especially binge drinking, the so-called holiday heart syndrome), nicotine, and stimulant medications (decongestants, ADHD medications, some asthma drugs) all activate the sympathetic nervous system and can trigger palpitations. Caffeine is a direct cardiac stimulant. Alcohol impairs heart muscle relaxation and can trigger atrial fibrillation. The blood test job here is to rule out other causes (thyroid, electrolytes) before attributing palpitations to lifestyle factors.
Typical pattern:
Palpitations within hours of consuming caffeine or alcohol, particularly when the dose is higher than usual. May resolve with abstinence. Often accompanied by tremor, anxiety, poor sleep, and increased urination.
What to do next: Track triggers in a diary for two weeks. Reduce caffeine to under 200 mg per day (one to two cups of coffee), avoid energy drinks, and limit alcohol to within Australian guidelines (no more than 10 standard drinks per week). Ask your GP for a TSH and electrolyte panel to confirm there is no medical contributor before attributing it solely to lifestyle.
Anxiety and Panic Disorder
How it causes palpitations: Anxiety and panic attacks activate the sympathetic nervous system, releasing adrenaline that increases heart rate and contractility. People with anxiety often become hyper-aware of normal heart sensations, creating a feedback loop where awareness of palpitations triggers more anxiety. While anxiety is a common cause of palpitations, blood tests are still essential to rule out medical drivers, since hyperthyroidism, anaemia, and B12 deficiency can all mimic or coexist with anxiety.
Typical pattern:
Palpitations triggered by stress or anxiety, often with chest tightness, breathlessness, dizziness, tingling around the mouth or fingers (from hyperventilation), and a sense of dread. May occur at rest or in response to specific situations.
What to do next: Get the medical workup first (TSH, FBC, electrolytes, B12, vitamin D). If those are normal, anxiety-driven palpitations respond to cognitive behavioural therapy, breathing techniques, regular exercise, reduced caffeine, and sometimes medication. Speak to your GP about a Mental Health Care Plan for Medicare-subsidised psychology sessions.
Tests to Ask Your GP For
This is the standard palpitations workup in Australia. Most are bulk billed under Medicare when ordered for a clinical indication. Your GP will usually order an ECG at the same visit and may organise a 24-hour Holter monitor if symptoms are intermittent.
| Test | Why It Matters | Cost |
|---|---|---|
| Thyroid Function (TSH, Free T4) | Hyperthyroidism is one of the most common medical causes of palpitations | Bulk billed |
| Full Blood Count (FBC) | Detects anaemia which forces the heart to compensate by beating faster | Bulk billed |
| Iron Studies (Ferritin, Iron, TIBC) | Iron deficiency is a major cause of palpitations in pre-menopausal women | Bulk billed |
| Electrolytes (Sodium, Potassium, Chloride, Bicarbonate) | Low potassium can cause arrhythmias | Bulk billed |
| Magnesium | Low magnesium destabilises the heart electrical system | Bulk billed |
| Calcium (corrected for albumin) | Both high and low calcium can disturb heart rhythm | Bulk billed |
| Kidney Function (eGFR, Creatinine, Urea) | CKD causes electrolyte imbalance and anaemia | Bulk billed |
| Fasting Glucose and HbA1c | Hypo- or hyperglycaemia can both produce palpitations | Bulk billed |
| Vitamin B12 and Folate | Deficiencies cause anaemia and autonomic dysfunction | Bulk billed |
| Lipid Profile | Cardiovascular risk assessment | Bulk billed |
| Plasma Metanephrines | Only if a phaeochromocytoma is suspected (episodic high BP and palpitations) | Medicare with indication |
Red Flags — When Palpitations Are Urgent
Most palpitations are benign, but some symptom combinations indicate a potentially dangerous arrhythmia or cardiac event and need same-day or emergency assessment.
How to Interpret Your Results
Standard pathology reports flag values outside the reference range but do not explain the implications for heart rhythm. SmarterBlood does. Upload your results and our AI looks at every marker that affects cardiac function and explains each in plain language.
Key reference ranges for palpitations workup:
- TSH: 0.4 to 4.0 mIU/L. Below 0.1 strongly suggests hyperthyroidism.
- Free T4: 9 to 19 pmol/L (range varies by lab).
- Haemoglobin: 120 to 160 g/L (women), 135 to 175 g/L (men).
- Ferritin: above 30 mcg/L (general); above 75 mcg/L if you also have RLS.
- Potassium: 3.5 to 5.0 mmol/L.
- Magnesium: 0.7 to 1.0 mmol/L.
- Calcium (corrected): 2.15 to 2.55 mmol/L.
- Sodium: 135 to 145 mmol/L.
- Fasting glucose: 4.0 to 5.5 mmol/L. Below 3.9 is hypoglycaemia.
Frequently Asked Questions
What blood tests should I have for heart palpitations?
Ask your GP for thyroid function (TSH and free T4), full blood count for anaemia, electrolytes (sodium, potassium, magnesium, calcium), kidney function, fasting glucose and HbA1c, and a fasting lipid profile. These cover the most common reversible causes.
Can low iron cause heart palpitations?
Yes. Iron deficiency anaemia reduces oxygen delivery, forcing the heart to beat faster and harder to compensate. Palpitations from anaemia are typically accompanied by fatigue, breathlessness on exertion, and pale skin. Treating the underlying iron deficiency usually resolves them.
Can an overactive thyroid cause palpitations?
Definitely. Hyperthyroidism is one of the most common medical causes. Excess thyroid hormone makes the heart beat faster and more forcefully and can trigger arrhythmias including atrial fibrillation. A simple TSH test is the first investigation.
What electrolyte imbalances cause palpitations?
Low potassium, low magnesium, and abnormal calcium levels can all cause palpitations and dangerous arrhythmias. People at risk include those on diuretics, with vomiting or diarrhoea, with eating disorders, or with chronic alcohol use. A simple electrolyte panel covers all of these.
When are heart palpitations dangerous?
Call 000 if palpitations are accompanied by chest pain, severe breathlessness, fainting or near-fainting, or last for hours without stopping. See your GP urgently if palpitations are frequent, increasing, or associated with a pulse over 130 at rest.
Can dehydration cause palpitations?
Yes. Dehydration reduces blood volume, which lowers blood pressure and makes the heart beat faster to compensate. It can also disturb sodium and potassium balance. Drinking water and replacing electrolytes usually resolves dehydration-related palpitations within hours.
How much caffeine is safe for someone with palpitations?
Most people tolerate up to 200 mg of caffeine per day (about one to two espressos), but sensitivity varies. If you get palpitations after coffee, try cutting back to one cup before noon, or switch to decaf. Avoid energy drinks entirely; they often contain 200 mg or more per serve plus other stimulants.
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