Which lab tests make sense for anxiety, depression, or fatigue?

Can depression be diagnosed with a blood test?

There is currently no blood test in routine clinical use that can confirm or rule out depression on its own.

Diagnosis is based on history, symptoms, their duration, functioning, and clinical evaluation. Lab tests can help identify conditions with similar symptoms, such as a thyroid disorder, or coexisting problems that need attention.

Supporting references: [1] NHS · Depression in adults.

Lab tests can therefore help identify a medical cause, detect a factor that worsens the condition, or check medication safety.

These are different purposes.

Finding a deficiency does not automatically show that it explains all the symptoms. And treating it does not rule out a need for psychotherapy, psychiatric medication, or another intervention as well.

The result needs to fit the person, rather than the other way around.

Before ordering tests, it helps to understand the fatigue

In a consultation, I would not start by ordering “comprehensive lab tests” without first clarifying what is happening.

I would ask whether the main problem is a lack of energy, sleepiness, physical weakness, exhaustion after exertion, or a loss of motivation. I would also ask when it started, how it is changing, and which activities it limits.

I would review sleep, diet, menstrual periods when relevant, weight changes, digestive symptoms, pain, substance use, and medication.

This helps determine what to investigate. Clinical protocols include lab tests when appropriate, rather than an identical panel for everyone with depressive symptoms.

Supporting references: [2] NHS Cornwall · Clinical protocol.

Two patients may say “I am exhausted” and need different evaluations.

The first useful test is a thorough medical history.

Which lab tests can provide information

Complete blood count and ferritin: they are not the same

A complete blood count can detect anemia and assess the characteristics of blood cells. Ferritin helps assess iron stores.

A person may have iron deficiency before developing anemia. That is why, when there are clues—for example, blood loss, an inadequate diet, or compatible symptoms—a normal blood count does not always complete the evaluation. Guidelines recommend looking for deficiency in people at risk, rather than indiscriminately screening the entire population.

Supporting references: [3] Government of British Columbia · Clinical guideline.

Ferritin also needs context: inflammation can raise it and make interpretation less straightforward.

If iron deficiency is confirmed, replacing iron is not enough. Its cause needs to be investigated. And it is not advisable to take iron indefinitely without confirming the need: not all anemia is caused by iron deficiency.

Supporting references: [3] Government of British Columbia · Clinical guideline.

The question would not simply be “is it low?” but “what does it mean in this situation, and what should we do with that information?”

Thyroid function: when checking TSH makes sense

Thyroid disorders can be mistaken for, or coexist with, emotional symptoms. NICE recommends considering thyroid function tests in people with depression or anxiety that is not adequately explained. An isolated symptom, however, does not establish thyroid disease.

Supporting references: [4] NICE · NG145.

In many adults, when a pituitary problem is not suspected, the evaluation begins with TSH. Depending on the result, testing is expanded to include free T4 and, in certain circumstances, free T3.

This does not mean always ordering every thyroid hormone and antibody test.

An acute illness can also temporarily affect results; tests should be ordered and interpreted at the appropriate time.

Supporting references: [4] NICE · NG145.

I would not attribute all distress to a minimal deviation or dismiss significant symptoms without examining the context.

Vitamin B12: especially when symptoms and risk factors are present

B12 deficiency can be accompanied by fatigue, cognitive difficulties, and neurological symptoms. It may also be associated with symptoms of anxiety, depression, or psychosis.

One important point is that it should not be ruled out solely because there is no anemia or increase in red blood cell size.

Supporting references: [5] NICE · NG239.

Testing should be considered when compatible symptoms are present along with factors such as a diet low in B12, gastrointestinal surgery, absorption problems, or certain medications. Nitrous oxide use is also a relevant part of the history.

Supporting references: [5] NICE · NG239.

This does not make B12 a universal explanation for “brain fog.” Results are interpreted alongside clinical findings and, if uncertain, may require further investigation.

Folate levels may be assessed in selected situations, rather than necessarily as part of every set of lab tests.

Supporting references: [2] NHS Cornwall · Clinical protocol.

Glucose, kidney function, liver function, and electrolytes

Glucose, kidney or liver function, and electrolytes may also be relevant in a targeted evaluation. Symptoms, existing conditions, medication, and examination findings determine what each test can contribute.

Supporting references: [2] NHS Cornwall · Clinical protocol.

For example, evaluating a person with no medical history would not have the same purpose as reviewing new fatigue in someone taking several medications who has known kidney disease.

There is no magic combination of lab measurements that can replace that distinction.

Vitamin D: neither a universal explanation nor a forbidden test

Vitamin D deserves its own section because it frequently comes up in consultations for fatigue and low mood.

The Endocrine Society’s 2024 guideline advises against routine testing in generally healthy people without an established indication. That recommendation concerns disease prevention: it does not mean that vitamin D should never be investigated in someone with symptoms or a specific medical situation.

Supporting references: [6] Endocrine Society · 2024 guideline.

In a consultation, I would decide whether there is a clinical reason to order the test and how I would interpret the result.

A low value does not, on its own, establish that it is the cause of depression. Likewise, correcting an abnormality does not mean ignoring other factors that sustain the condition.

I would not suggest pursuing ever-higher “optimal” levels or taking high-dose supplements simply because someone feels tired.

Testing and treatment should be based on an indication, rather than a vitamin’s popularity.

Does testing cortisol make sense if I am very stressed?

I would not use a single cortisol measurement as a general gauge of “how stressed” a person is.

Cortisol changes throughout the day and can be influenced by exercise, stress, pregnancy, and medication. Cortisol tests are useful for investigating specific conditions, such as Cushing’s syndrome or adrenal insufficiency, using the appropriate sample type and protocol.

Supporting references: [7] MedlinePlus · Laboratory tests.

Investigating a suspected endocrine disorder is different from ordering a “stress profile” for any anxiety.

It is also helpful to distinguish adrenal insufficiency, which is a real medical condition, from so-called “adrenal fatigue.” The Endocrine Society states that the latter has no validated diagnostic test and that tests marketed to detect it lack sufficient evidence.

Supporting references: [8] Endocrine Society · Patient information.

This distinction does not deny the exhaustion.

It avoids explaining it with a label that can divert attention from what actually needs evaluation.

What about a complete hormone panel?

I would not order one automatically either.

The phrase “I am hormonal” can refer to very different experiences. Before ordering tests, it helps to learn about menstrual changes, vasomotor symptoms, sexual function, medication, and other relevant information.

One example illustrates the limits of measuring more: in people 45 years or olderwho are otherwise healthy and have typical symptoms, NICE recommends identifying perimenopause or menopause clinically, without routine hormone tests. Other situations may require a different evaluation.

Supporting references: [9] NICE · NG23.

The fact that hormones matter does not mean that a broad panel is always the best way to understand them.

Gut health and mental health: investigating what is relevant without confusing it with just any test

The gut-brain axis is an important area of research. But recognizing that connection does not automatically validate every commercial test.

An international consensus published in The Lancet Gastroenterology & Hepatology in 2025 concluded that the evidence is still insufficient to broadly recommend routine microbiome profiling in clinical practice. It also warned about commercial interpretations and recommendations that go beyond what has been demonstrated.

Supporting references: [10] The Lancet Gastroenterology & Hepatology · Consensus.

I would not use a “dysbiosis” report as sufficient evidence of the cause of depression, or as the sole basis for choosing a psychiatric treatment.

That is different from investigating a specific digestive problem. Persistent digestive symptoms, weight loss, or unexplained deficiencies in iron, B12, or folate may justify investigating celiac disease, among other possibilities.

Supporting references: [11] NICE · NG20.

The difference lies in the clinical question.

It would not be “let us measure everything we can in the gut,” but “are there signs of a disease for which we have useful tests?”

Some lab tests are ordered because of medication, rather than to establish a diagnosis

This distinction is especially important in Psychiatry.

Some treatments require specific safety monitoring, even when the person feels emotionally well.

This is not a complete list of monitoring requirements for all psychiatric medications.

Nor does it mean that any fatigue during treatment is a serious complication. It means that the specific medication changes the questions we need to ask.

And normal safety lab results do not establish that there are no other side effects that need review.

Related reading: Sexual side effects of antidepressants.

“Everything is normal”: what we can and cannot conclude

A result within the reference range is useful information. It is not a certificate that every possible cause has been investigated.

Likewise, an asterisk does not automatically indicate a disease. Reference ranges come from reference populations, may vary between laboratories, and must be interpreted alongside symptoms and other information.

Supporting references: [16] MedlinePlus · Laboratory results.

That is why I would not make a diagnosis based on a red mark in a report or dismiss someone’s distress because there are none.

Some problems also cannot be evaluated through blood tests alone. For example, suspected sleep apnea may require recording breathing and other variables overnight. Repeating normal lab tests does not replace that study when it is indicated.

Supporting references: [17] NHS · Sleep apnea.

The appropriate response may be to expand testing, confirm a finding, use a different type of examination, or focus on clinical evaluation.

It is not always a matter of ordering more of the same.

Before the blood draw: a supplement can change the result

It is advisable to report everything you take, including nonprescription products.

The supplement biotin, found in some hair, skin, and nail supplements, can interfere with certain thyroid tests and produce falsely high or low values. The AEMPS recommends telling your doctor and the laboratory that you use it.

Supporting references: [18] AEMPS · Safety · January 2023.

This does not mean that you should stop taking it for a fixed number of days based on generic advice. Instructions depend on the product, dose, and testing method used.

When measuring levels of certain medications, the timing of the blood draw relative to the last dose also matters. For lithium, there are specific conditions that make the result interpretable.

Supporting references: [12] NHS SPS · Medication safety.

A well-chosen test also needs proper preparation.

What I would do with the results in a consultation

I would do more than read aloud which values are outside the range.

For each finding, I would try to answer:

Could it explain a significant part of the symptoms? Does it need confirmation? Does it require treatment or referral? What do we expect to change with intervention?

I would then agree on how to monitor progress.

If we correct a deficiency, it is useful to assess both the laboratory and clinical response. If symptoms persist, I would not automatically assume that the supplement needs to be increased further or that we need to find another abnormal value.

And if no sufficient medical cause is found, I would continue evaluating mood, anxiety, sleep, substance use, and functioning. The absence of a blood test finding does not remove the need to address those aspects.

Supporting references: [20] NIMH · Clinical information.

The purpose of investigating is not to find something abnormal at any cost. It is to make better decisions.

Related reading: My antidepressant is not working: when to review treatment.

Do I need to have every test before starting treatment?

You do not need to arrange a battery of lab tests on your own before booking an appointment.

You can bring the results you already have. The evaluation will determine whether they provide enough information and what is actually missing.

I would not suggest putting care for distress on hold indefinitely while physical factors are investigated either. In my approach, medical investigation and psychological or psychiatric care can be coordinated according to the situation.

Thorough investigation does not mean delaying necessary help.

Do you have anxiety, fatigue, or low mood and are unsure what has actually been investigated?

An evaluation can help organize the symptoms, review available test results, and decide which lab tests or examinations make sense.

The aim is not to offer identical “comprehensive lab tests” for everyone, but to integrate physical health, sleep, medication, nutrition, and emotional well-being into an individual plan.

Dr. Marc Agraz · Integrative psychiatry
In-person care in Lleida and online consultations when clinically appropriate, with coordination with other professionals when needed.

Practice information: Frequently asked questions about the practice.

To prepare for your visit, bring your previous lab results with dates, a list of medications and supplements, and a brief explanation of what has changed. You do not need to request new tests before the evaluation.

You do not need to prove that your distress shows up in a lab test for it to deserve attention. You need an evaluation that connects the results with what you are experiencing.

Educational content for adults. The tests described are examples, not an individual prescription. Do not start supplements or change medication based solely on this article. Scheduled consultations are not an emergency service.

Frequently asked questions

Sources and reference resources