Blood tests cannot diagnose depression, anxiety, or any other mental health condition. Doctors diagnose these conditions through a clinical assessment with a doctor. But blood tests do two important jobs: they help rule out physical conditions that can look like mental health symptoms, and they keep some medicines safe.
There is no single set of blood tests that everyone needs before mental health treatment. Your GP or psychiatrist will choose tests based on your symptoms, medical history and the medicine being considered. Some people need only a few investigations, while others require regular monitoring throughout treatment.
Here is what to know before your GP or psychiatrist sends you for bloods:
- Bloods can find or rule out “mimics”, such as a thyroid problem, low iron, low vitamin B12 or diabetes.
- Some medicines need a baseline test and regular checks. This includes lithium, antipsychotics and some mood stabilisers.
- Many common antidepressants don’t need routine blood monitoring for most people.
- Your GP and psychiatrist can share results, so you don’t need to be tested twice.
- Physical health checks matter because mental illness is linked to higher rates of heart disease and diabetes.
Can a Blood Test Diagnose Depression or Anxiety?
No. Depression and anxiety are diagnosed by talking with a doctor about your symptoms, history, and daily life. Blood tests support that process by checking whether something else, such as a thyroid or vitamin problem, could be adding to how you feel.
Researchers are studying “biomarkers”, which are measurable signs in the blood that might one day help with diagnosis. Nothing is ready for routine use yet.
A normal result also doesn’t mean “it’s all in your head”. It means a physical cause is less likely, so your care can focus on the right treatment.
Part 1: Blood Tests That Rule Out Medical Causes of Mental Health Symptoms
Tiredness, low mood, poor focus, and anxiety can come from many causes. Your GP may order blood tests to check for physical conditions that cause the same symptoms. Healthdirect notes that GPs may test for anaemia, thyroid problems, and diabetes, which can look like depression.
| Test | What it checks | Why it matters for mood |
|---|---|---|
| Full blood count (FBC) | Anaemia and signs of infection | Can cause tiredness and low energy |
| Thyroid function (TSH) | An under- or overactive thyroid | Can cause low mood or anxiety |
| Iron studies (ferritin) | Iron stores | Low iron can cause fatigue and poor concentration |
| Vitamin B12 and folate | Vitamin deficiency | Can affect energy, memory and mood |
| Glucose and HbA1c | Blood sugar, including diabetes | Can cause fatigue and mood changes |
| Kidney and liver function (UEC/eGFR, LFTs) | General health | Also helps with safe prescribing later |
| Calcium and sodium | Salt and mineral balance | Abnormal levels can affect mood and cause confusion |
| Vitamin D | Vitamin D levels | Only for people in risk groups |
Not everyone needs every test. Your doctor chooses based on your symptoms, age, history, and current medicines.
TSH test is often the first check, and it is directly linked to thyroid function and mood symptoms. If tiredness is a big part of how you feel, it helps to understand low iron and ferritin testing. Vitamin D isn’t checked for everyone; learn when vitamin D testing is recommended and what the evidence says about mood.
Blood Tests for Anxiety: What's Usually Checked
For anxiety, doctors usually look at thyroid function (an overactive thyroid can feel like anxiety) and blood glucose. Sometimes they add a full blood count. They will also ask about caffeine, alcohol, other substances, and any medicines you take, because these can cause anxiety symptoms too.
When Other Tests Are Needed
Depending on your symptoms and medical history, your doctor may recommend additional tests. These could include a sleep study for persistent snoring, urine tests to investigate certain symptoms, or an ECG (heart tracing) before some medicines.
Part 2: Blood Tests Before and During Psychiatric Medication
Some psychiatric medicines need a baseline blood test before you start, then regular checks. These tests check medication levels and potential side effects. Baseline tests are usually planned as part of psychiatric assessment and medication management before a new medicine is started.
Medicine Type | Typical Checks | Why |
Lithium | Lithium level, kidney function (eGFR), thyroid, calcium, weight | The safe range is narrow, and long-term use can affect the kidneys and thyroid |
Antipsychotics | Weight, waist, blood pressure, glucose or HbA1c, cholesterol (sometimes prolactin and liver tests) | Some can cause weight gain, higher blood sugar and higher cholesterol |
Clozapine | Very regular full blood counts, plus heart checks early on | Rare but serious effects on white blood cells and the heart |
Some mood stabilisers (such as valproate or carbamazepine) | Liver function, full blood count, sodium | To pick up side effects early |
Antidepressants | Usually no routine bloods; sodium may be checked in some older adults | Most people don’t need regular blood monitoring |
ADHD medicines | Usually blood pressure, heart rate and weight rather than bloods | Cardiovascular and growth checks |
Note: Your prescriber sets your schedule. This table is a general guide only.
How Often Is Lithium Monitoring Needed?
Lithium remains an important part of bipolar disorder treatment for many people, which is why regular monitoring matters. Checks are more frequent at the start, then settle into a routine. Many guidelines suggest lithium levels about every three months and kidney and thyroid tests about every six months, but your prescriber will confirm what applies to you.
The news here is reassuring. Australian Prescriber reports that most people on lithium have no kidney effects, and about 1% develop end-stage kidney failure over 15 years. Monitoring is how problems are caught early.
Timing matters. The lithium level is usually taken about 12 hours after your last dose, so ask your prescriber when to take your dose before the test.
Seek medical help promptly if you have vomiting, diarrhoea, a worsening tremor or confusion while taking lithium.
Metabolic Monitoring for Antipsychotics
Regular physical health checks are a key part of schizophrenia care and support, especially for people taking antipsychotics long-term. Some of these medicines can increase weight, blood sugar, and cholesterol, so doctors monitor these over time.
The Australian Diabetes Society describes a typical schedule:
- Weight, waist measurement, and blood pressure every 3 to 6 months
- Blood glucose every 6 months
- Cholesterol (lipids) at least once a year
- More frequent checks when starting or changing a medicine
Clozapine Blood Monitoring
Clozapine has its own strict schedule. Australian Prescriber describes a weekly full blood count for the first 18 weeks, then every four weeks. If you have a fever, sore throat, or signs of infection, contact your doctor urgently.
Clozapine requires strict blood count monitoring because it can dangerously reduce white blood cells. Under the established Australian schedule, blood counts are checked weekly for the first 18 weeks and at least every four weeks thereafter. Additional monitoring may be needed for cardiac complications, particularly early in treatment. Fever, a sore throat or signs of infection need urgent medical assessment.
Why Physical Health Checks Matter in Mental Health Care
Equally Well Australia highlights the shorter life expectancy of people living with severe mental illness. Research published in the Medical Journal of Australia found that they can die up to 20 years earlier than the general population, often from preventable physical health conditions such as heart disease and diabetes. Most of these deaths are from preventable conditions such as heart disease, diabetes, and lung disease.
Part of the problem is “diagnostic overshadowing”. This is when a physical symptom is put down to a person’s mental health and not investigated properly.
Monitoring is also not always completed. A survey in Australasian Psychiatry (2016) found that fewer than half of the psychiatrists surveyed routinely checked weight, glucose, or lipids. A 2025 study in the ANZ Journal of Psychiatry found that only 1.5% of children and teens newly prescribed antipsychotics had full metabolic monitoring within 12 months.
This isn’t about blame. Busy systems and shared responsibility can make gaps easy. It’s simply about recognising that blood tests can play an important role in optimising overall health and well-being.
Who Organises Mental Health Blood Tests: GP or Psychiatrist?
Either can order them. Often the GP handles ongoing monitoring under a shared-care plan, while the psychiatrist manages the medicine. Ask your care team who is responsible for which test, so nothing is missed.
Shared care works best when results travel between your doctors. Ongoing monitoring is often handled through GP care and pathology review, with results shared with your psychiatrist. That means fewer repeat tests and appointments. Some services, such as Elysea Health, offer GP and psychiatry care under one roof, which is one way this can work.
How to Prepare for Your Blood Tests
- Ask whether you need to fast, as some glucose and cholesterol tests require it.
- For lithium, ask when to take your dose before the test.
- Bring a list of all medicines and supplements. Some supplements can affect results; for example, biotin can interfere with some thyroid tests.
- Ask whether the test is bulk billed. Many pathology tests are.
- Keep your own record of results and dates.
- Don’t stop or change your medicine because of a result. Talk to your prescriber first.
Frequently Asked Questions
Why do antipsychotics need blood sugar and cholesterol checks?
Some antipsychotics can affect how the body handles sugar and fat, which can raise the risk of diabetes and heart problems. Regular checks let your care team spot small changes early and adjust your plan before they become bigger issues.
Can my GP organise the blood tests my psychiatrist asks for?
Yes, in many cases. Your psychiatrist can send a written request, and your GP can order the tests and follow results locally. Under a shared-care plan, both doctors see the results. Confirm with them who is responsible for each test.
Do I need to fast before mental health blood tests?
It depends on the test. Glucose and cholesterol checks sometimes need fasting, while many others, such as a full blood count, don’t. The pathology request or your doctor will say. If unsure, ask before the day.
What if my blood tests come back normal but I still feel unwell?
A normal result is useful information. It means a physical cause is less likely, so your doctor can focus on assessing and treating your mental health. Your symptoms are real either way. Go back to your doctor if they continue or change.
How often do I need blood tests on lithium?
Monitoring is more frequent when you start lithium or change your dose. Once treatment is stable, checks continue at regular intervals. Your prescriber will confirm the timing for your lithium level, kidney function, thyroid function, and calcium tests.
If you’re struggling or having thoughts of suicide: Lifeline 13 11 14 | Suicide Call Back Service 1300 659 467 | Kids Helpline 1800 55 1800 (ages 5 to 25) | In an emergency call 000.
The content on the website is for general information and may be prepared or reviewed by clinicians or the Elyséa HEALTH team. It is not a substitute for personalized medical advice. While we try to keep the information accurate and up to date, we cannot guarantee it is complete or suitable for your individual situation.
