Blood tests for anxiety: what they can find and what they can't

No blood test diagnoses anxiety, but a few tests find physical causes of the same pounding heart, shaky hands, sweating and broken sleep: mainly an overactive thyroid, low iron, low vitamin B12, blood sugar problems and high calcium. Below are the tests to ask for, the result on each that changes the plan, how strong each link to anxiety is, and what to do next whether your results come back abnormal or normal.

Can a blood test show anxiety?

A blood test can answer one question about anxiety: is a physical cause producing these symptoms? An anxiety disorder is a pattern of worry, fear and avoidance that lasts and gets in the way of life, and that pattern has no blood marker. Researchers have built experimental blood panels that read gene activity, but none is used in clinical care, and no lab test sold to the public diagnoses anxiety.

That makes blood tests most useful for a specific group of people: anyone whose anxiety began suddenly with no obvious trigger, whose symptoms are mostly physical, or who has another clue such as weight loss, heavy periods or a new medicine. For them, a normal panel is as useful as an abnormal one.

What anxiety is, and how it is diagnosed

Generalized anxiety disorder (GAD) is persistent worry about many everyday things that is hard to control and lasts six months or more. Panic disorder is repeated, unexpected panic attacks: sudden surges of intense fear that peak within minutes, with a pounding heart, sweating, trembling or breathlessness. Social anxiety disorder and specific phobias center on particular situations or objects. Anxiety disorders are common: in the US about 19% of adults have one in a given year, women more often than men (23% vs 14%) ⁸. All of them are diagnosed clinically, from what you describe, and the UK's NICE guideline for anxiety builds its whole pathway on that assessment ¹.

Doctors often start with the GAD-7, a seven-question form about the past two weeks. Its first two questions are the core of the disorder:

Over the last 2 weeks, how often have you been bothered by the following problems? Feeling nervous, anxious, or on edge. Not being able to stop or control worrying.GAD-7 questionnaire, Spitzer RL et al., Archives of Internal Medicine, 2006 ²

The other five ask, over the same two weeks, how often you have been bothered by:

• Worrying too much about different things.
• Trouble relaxing.
• Being so restless that it is hard to sit still.
• Becoming easily annoyed or irritable.
• Feeling afraid, as if something awful might happen.

Score each of the seven: 0 for not at all, 1 for several days, 2 for more than half the days, 3 for nearly every day. Add them up for a total from 0 to 21.

Scores of 0 to 4 are minimal, 5 to 9 mild, 10 to 14 moderate and 15 to 21 severe. A score of 10 or more is the usual point for a fuller assessment. In the study that built the questionnaire, the cut-off of 10 picked up 89% of people who had GAD and correctly cleared 82% of people who did not ². A clinician still makes the diagnosis.

Physical symptoms of anxiety that other conditions also cause

Each physical symptom of anxiety has a short list of physical causes, and the table maps each one to the test that checks it.

Some features make a physical cause more likely and are worth telling your doctor about directly:

• Anxiety that starts for the first time after 40 with no life trigger.
• Weight loss despite a normal or bigger appetite, heat intolerance, or a visible tremor.
• Episodes of pounding headache, sweating and palpitations together, especially with high blood pressure.
• Symptoms tied to meals or long gaps without food.
• Heavy periods, a vegan diet, weight-loss surgery, or long-term use of metformin or acid-reducing pills (all raise the chance of low iron or low B12).
• A new medicine, a dose change, or cutting down on alcohol in the weeks before symptoms began.

If a racing heart comes with chest pain, fainting or breathlessness, or this is a first panic-like attack after 40 or with heart disease, call 911 now rather than waiting for blood tests. If the main symptom is your heart, our page on heart palpitations covers the rhythm side in depth; for pins and needles, see tingling hands and feet; if it is heat and sweating in your 40s, see perimenopause and hot flashes.

The blood tests worth doing, and what each one can find

The table gives the result that changes something on each test, in US units with SI units (the metric units used in the UK and most of the world), and how strongly each finding connects to anxiety symptoms. Lab reference ranges vary, so read your number against the range printed on your own report.

Hemoglobin, the oxygen-carrying protein in red cells, counts as low under 12 g/dL in women or 13 g/dL in men (120 / 130 g/L). A low sodium has its own causes, covered in low sodium.

Thyroid: the strongest link

An overactive thyroid (hyperthyroidism) speeds up the whole body. TSH, thyroid-stimulating hormone, is the pituitary gland's signal to the thyroid, and it drops when the thyroid overworks. The American Thyroid Association lists nervousness, anxiety, tremor, palpitations, heat intolerance and weight loss among the common symptoms, and recommends TSH as the first test, adding free T4 and total or free T3 when TSH is low ³. It is the physical cause with the clearest link to anxiety, and anxiety symptoms caused by it often ease once the thyroid is treated, though some can outlast the fix. Too high a dose of thyroid medicine causes the same picture. Our thyroid panel guide and TSH vs free T4 walk through the patterns, and hyperthyroidism covers causes and treatment. An underactive thyroid is more often linked to low mood and fatigue than to anxiety.

Iron and B12: low stores before a low count

Iron deficiency drains energy and makes the heart work harder, and it can show up as a low ferritin while hemoglobin is still normal, before anemia develops. A ferritin under 15 ng/mL is the World Health Organization's cut-off for deficiency in healthy adults, and many clinicians treat under 30 ng/mL as deficiency when symptoms fit. Ferritin has one catch, which our ferritin vs iron guide puts this way: "Inflammation raises ferritin and lowers serum iron at the same time, so a normal ferritin during illness can hide deficiency and a low serum iron can appear with full stores." See iron deficiency for causes.

Vitamin B12 deficiency affects the nerves and brain. In a 1988 New England Journal of Medicine series, 28% of people with nerve or mental symptoms from B12 deficiency had no anemia and no enlarged red cells, so a normal blood count does not rule B12 out ⁴. When B12 lands in the borderline 200 to 300 pg/mL band, a methylmalonic acid (MMA) test usually settles it. See B12 deficiency for causes.

Blood sugar and calcium

Low blood sugar sets off an adrenaline response: tremor, sweating, a racing heart, hunger and a surge of anxiety. A fasting glucose taken on a calm morning rarely catches it; the useful reading is one taken during a spell. Outside diabetes treatment, true lows are uncommon, and as our hypoglycemia page puts it: "For people on insulin or sulfonylureas, any reading under 70 mg/dL is a low to treat; for everyone else, a low disorder is diagnosed only when symptoms, a low reading at that moment and relief after sugar all line up." A high HbA1c points to diabetes rather than anxiety; HbA1c explains the bands.

High calcium, usually from an overactive parathyroid gland, causes restlessness, poor sleep, low mood and thirst; high calcium and hyperparathyroidism cover the next steps.

Vitamin D and magnesium: weak evidence

Low vitamin D and low magnesium are common in people with anxiety, but studies of correcting them have not shown a clear effect on anxiety itself. A 2017 systematic review of magnesium found only possible benefit for self-rated anxiety, from trials of poor quality ⁷. Only about 1% of the body's magnesium is in the blood, so a normal serum result says little about stores; a red-cell test (magnesium, RBC) is sometimes used, though it is not a perfect measure either. Both are reasonable to check if you have other risk factors; neither is a likely sole cause. If yours came back low, vitamin D deficiency and magnesium deficiency explain what the number means and how it is corrected. If your vitamin D report uses the other unit, convert it here.

CalculatorVitamin D converterVitamin D in nmol/L or ng/mL? Convert it both ways before comparing with the cut-offs above.Work it out

Tests a doctor may add, and ones to skip

For symptoms that follow your cycle, see PMS and hormonal imbalance. A single morning cortisol is a poor anxiety test. Cortisol rises with stress, sleep loss and the time of the draw, and a high morning value most often reflects the moment rather than a disease; see high morning cortisol and how to lower cortisol. Doctors screen for Cushing's syndrome with the late-night, 24-hour or dexamethasone tests in the table ¹⁰. Pheochromocytoma, a rare adrenal tumor that releases bursts of adrenaline, is checked with metanephrines, and only when the episodic pattern is there ⁵.

Three tests sold for anxiety add little: multi-point saliva cortisol panels for "adrenal fatigue" (a diagnosis endocrinologists do not recognize; see adrenal fatigue), IgG food sensitivity panels, and urine neurotransmitter tests. None of them changes what a doctor would do next. For the wider question of which tests suit you, see what blood tests should I get.

The everyday causes no blood test shows

Caffeine is one of the most common physical drivers of jittery anxiety. The FDA cites 400 mg a day, about four or five cups of coffee, as an amount not generally linked to harmful effects in healthy adults, and notes that sensitivity varies and that too much can cause anxiety, jitters and a fast heartbeat ⁶. People with panic disorder often react to far less. The amounts below are approximate typical figures; brands vary widely.

Many clinicians suggest cutting back on caffeine for a couple of weeks, tapering over a few days to avoid withdrawal headaches, and noting whether the jitters and racing heart ease. If they do, that points to caffeine; tell your clinician either way.

Alcohol calms for a few hours and then rebounds: as it wears off, the nervous system swings the other way, and next-morning anxiety is common. Our guide to alcohol and blood tests covers what regular drinking does to results. Nicotine, cannabis (especially high-THC products) and short sleep all raise anxiety, and can't sleep covers the sleep side.

Medicines that commonly cause anxiety or jitteriness include stimulants for ADHD, steroid tablets, asthma inhalers such as albuterol, decongestants containing pseudoephedrine, a thyroid hormone dose that is too high, and the first weeks of an SSRI antidepressant. If you suspect a medicine, raise it with your prescriber rather than stopping it yourself.

If a result comes back abnormal

1. 1Low TSHFree T4 and T3, then a search for the cause of an overactive thyroid. If you take levothyroxine, your prescriber may review the dose.
2. 2Low ferritin or hemoglobinFinding why iron is low matters as much as replacing it, especially with heavy periods or gut symptoms. See iron deficiency.
3. 3Low or borderline B12Often an MMA test, then treatment and a look for the cause, such as diet, metformin or absorption problems.
4. 4Low glucose during symptomsYour doctor may ask you to check your blood sugar with a finger-prick meter during spells and note the time and your last meal, then bring several readings back before any further testing. A low with confusion, fainting or being unable to eat or drink is an emergency: call 911.
5. 5High calciumA repeat calcium with parathyroid hormone (PTH) to check for hyperparathyroidism. Very high calcium with confusion, vomiting, severe thirst or weakness needs same-day care.

Fixing a deficiency helps the share of symptoms that deficiency caused. Anxiety disorders can sit alongside a thyroid or iron problem, so if anxiety persists once a result has been corrected and rechecked, treat that as its own question for your doctor. Your clinician will set when each result is rechecked, often after a few weeks to a few months of treatment.

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If your bloods are normal

Normal results make the common physical causes unlikely, so the next step is talking with your clinician about whether an anxiety disorder fits; anxiety disorders are common and treatable. Everyday stress usually fades when its trigger goes, while an anxiety disorder persists without one. NICE recommends stepped care: education and monitoring first, then guided self-help, then individual CBT (cognitive behavioral therapy, a structured talking therapy that teaches you to spot and change anxious thought patterns) or applied relaxation (a taught technique for relaxing your muscles quickly when anxiety starts), or a medicine, with sertraline (an SSRI) as the first-choice drug ¹. NICE advises against benzodiazepines for generalized anxiety except briefly during a crisis ¹. Regular exercise helps alongside these. Some doctors prescribe a beta-blocker for a racing heart and tremor in specific situations such as public speaking; it does not treat the worry, it is not suitable for everyone (for example people with asthma), and it is a decision for your prescriber.

Some people look at supplements. The evidence for each is thinner than the marketing suggests, and none of these is a treatment for an anxiety disorder. If you take an SSRI, a sedative or thyroid medicine, or are pregnant, ask your clinician or pharmacist before adding one.

Supplements studied for stress and self-rated anxiety

Mixed evidenceMagnesiumA 2017 systematic review found possible benefit for self-rated anxiety in anxiety-prone people, from trials of poor quality [[7]].In our shop

Early evidenceL-theanineSmall trials report calmer self-rated stress; few studies in diagnosed anxiety disorders.In our shop

Mixed evidenceAshwagandhaSeveral short trials report lower self-rated stress and anxiety scores; most are small [[9]].In our shop

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