Why Your Psychiatric Provider May Order Labs
Written by Dr. Oswaldo Romero, PMHNP-BC
When people think about psychiatry, they think about conversations, and not blood draws. So it can come as a surprise when a psychiatric provider hands over a lab order. Why would a mental health clinician need blood work?
The answer is straightforward: psychiatric care is medical care. The brain does not operate in isolation from the rest of the body. Hormones, organ function, nutrient levels, metabolic health, and even the medications used to treat psychiatric conditions all have measurable, testable biological dimensions. Laboratory testing is one of the most important tools a psychiatric provider has. This is not to replace the clinical interview, but to make it more complete.
Here is why labs matter, what they are looking for, and when to expect them.
Reason #1: Ruling Out Medical Conditions That Look Like Mental Illness
One of the most important reasons a psychiatric provider orders labs is to make sure that what looks like a psychiatric condition is not actually a medical one.
This is not a rare concern. Research published in the New England Journal of Medicine notes that in the general hospital setting, up to one-third of patients who present with depressive symptoms may have an underlying medical condition contributing to or causing those symptoms. Conditions that can mimic depression, anxiety, or even psychosis include:
- Hypothyroidism — an underactive thyroid can cause fatigue, low mood, weight gain, cognitive slowing, and depressive symptoms that are virtually indistinguishable from major depressive disorder
- Anemia — low red blood cell counts can cause fatigue, difficulty concentrating, and irritability
- Vitamin B12 and folate deficiencies — these can present with depression, cognitive impairment, and even psychotic symptoms in severe cases
- Diabetes and blood sugar dysregulation — both high and low blood sugar can affect mood, energy, and cognition
- Electrolyte imbalances — abnormal sodium, calcium, or potassium levels can cause confusion, mood changes, and altered mental status
- Liver and kidney dysfunction — impaired organ function can affect how the body processes medications and can produce psychiatric symptoms directly
- Substance use — drugs and alcohol can cause or worsen virtually every psychiatric symptom, and a urine toxicology screen can provide critical diagnostic information
A basic set of labs: typically including a complete blood count, comprehensive metabolic panel, thyroid-stimulating hormone, and sometimes vitamin B12, folate, and a urine drug screen, helps the provider distinguish between a primary psychiatric condition and a medical condition that needs a different kind of treatment entirely. Treating someone for depression when the real problem is hypothyroidism, for example, means the patient suffers unnecessarily while the actual cause goes unaddressed.
Reason #2: Establishing a Baseline Before Starting Medication
Many psychiatric medications affect the body in ways that need to be monitored. Before starting a new medication, a provider often needs to know where a patient's baseline numbers stand, so that any changes can be detected early and managed proactively. This is not about expecting problems. It is about practicing safe, evidence-based medicine.
The specific labs depend on the medication being considered:
- Lithium is one of the most effective medications for bipolar disorder, but it is processed by the kidneys and affects the thyroid. Before starting lithium, baseline labs typically include kidney function tests (creatinine, estimated glomerular filtration rate), thyroid-stimulating hormone, calcium, and a complete blood count. Once a stable dose is established, lithium levels, kidney function, and thyroid function are monitored regularly — generally every three to six months.
- Valproate (Depakote) is a mood stabilizer that can affect the liver and blood cell counts. Baseline labs include liver function tests and a complete blood count. Serum drug levels are monitored to ensure the medication is in the therapeutic range — typically 50 to 100 micrograms per milliliter. Liver function and blood counts are rechecked periodically, especially during the first year.
- Carbamazepine (Tegretol) also requires monitoring of liver function, blood counts, and electrolytes. It can cause a rare but serious drop in white blood cells and can affect sodium levels. Monthly blood counts and liver function tests are recommended for the first three months, then annually.
- Atypical antipsychotics — medications like quetiapine, olanzapine, risperidone, and aripiprazole — are associated with metabolic side effects including weight gain, elevated blood sugar, and changes in cholesterol and triglyceride levels. Guidelines recommend checking fasting glucose (or hemoglobin A1c) and a fasting lipid panel before starting these medications, again at 12 weeks, and then annually. Weight and blood pressure should be monitored at every visit for the first six months.
- Clozapine, used for treatment-resistant schizophrenia, requires mandatory blood monitoring through a Risk Evaluation and Mitigation Strategy (REMS) program because of the risk of agranulocytosis — a dangerous drop in white blood cells. Regular complete blood counts with absolute neutrophil counts are required throughout treatment.
These are not optional extras. They are part of the standard of care, recommended by organizations including the American Psychiatric Association, the American Academy of Child and Adolescent Psychiatry, the Canadian Network for Mood and Anxiety Treatments (CANMAT), and the International Society for Bipolar Disorders (ISBD).
Reason #3: Monitoring Medication Levels
Some psychiatric medications have what is called a narrow therapeutic window — meaning the difference between a dose that works and a dose that is toxic is relatively small. For these medications, periodic blood draws to check drug levels are essential.
Lithium is the classic example. The target serum level for lithium in acute treatment is 0.8 to 1.2 mEq/L, while maintenance levels of 0.6 to 1.0 mEq/L may be sufficient. Levels above the therapeutic range can cause toxicity — symptoms ranging from tremor and nausea to confusion, seizures, and kidney damage. Levels below the therapeutic range may mean the medication is not working. Blood is drawn approximately 12 hours after the last dose (the "trough" level), and levels are checked after every dose change and then every three to six months once stable.
Valproate levels are similarly monitored, with a target range of 50 to 100 micrograms per milliliter. Research has shown a linear relationship between serum valproate levels and therapeutic efficacy in acute mania, with higher levels associated with greater effectiveness.
Carbamazepine levels are monitored primarily to ensure they are not in the toxic range and to check for treatment adherence, as the relationship between serum level and clinical efficacy is less well established.
Therapeutic drug monitoring is not just about safety — it is also about effectiveness. Studies have found that approximately one-third of patients on lithium or valproate have subtherapeutic drug levels during treatment, meaning their medication may not be working as well as it could. A simple blood draw can identify this problem and guide a dose adjustment that makes a meaningful difference.
Reason #4: Watching for Metabolic Changes
This deserves its own section because it is one of the most clinically significant, and most underappreciated, easons for lab monitoring in psychiatry.
Second-generation antipsychotic medications are widely prescribed not just for psychosis, but also for bipolar disorder, treatment-resistant depression, and anxiety. These medications can cause significant metabolic changes, including:
- Weight gain — some antipsychotics, particularly olanzapine and clozapine, are associated with substantial weight gain that can begin within the first few weeks of treatment
- Elevated blood sugar and insulin resistance — the American Diabetes Association recommends that patients on second-generation antipsychotics be screened for prediabetes or diabetes at baseline, rescreened at 12 to 16 weeks after starting the medication, and annually thereafter
- Dyslipidemia — elevated triglycerides and cholesterol increase cardiovascular risk over time
- Metabolic syndrome — the clustering of abdominal obesity, high blood pressure, elevated blood sugar, and abnormal lipid levels
These changes are more predictable than they are treatable once established, which is why early detection through lab monitoring is so important. If metabolic changes are caught early, the provider can intervene — by switching to a lower-risk medication, adding metformin, or intensifying lifestyle counseling — before the consequences become serious.
An NEJM review on schizophrenia recommends monitoring body weight, blood pressure, and heart rate at every visit for six months after starting a new antipsychotic, with fasting glucose and lipid panels checked at baseline, at 12 weeks, and annually thereafter.
Reason #5: Pregnancy Planning and Reproductive Safety
Several psychiatric medications are known teratogens — meaning they can cause birth defects if taken during pregnancy, particularly during the first trimester. Valproate and carbamazepine carry the highest risk and are generally not recommended for women of childbearing age unless no safer alternative exists.
A pregnancy test is a standard part of the baseline lab workup for any woman of reproductive age who is being considered for these medications. This is not about making assumptions — it is about ensuring safety before starting a medication that could cause harm.
Additionally, some antipsychotic medications can elevate prolactin levels, which can lead to menstrual irregularities, galactorrhea (unexpected breast milk production), and sexual dysfunction. If a patient reports these symptoms, a prolactin level may be checked to determine whether the medication is the cause.
Reason #6: Ongoing Safety During Long-Term Treatment
Psychiatric treatment is often long-term, and the body changes over time. A medication that was well-tolerated at the start of treatment may begin to affect organ function months or years later. This is why lab monitoring does not stop after the initial workup — it continues throughout treatment.
For patients on lithium, long-term monitoring of kidney function and thyroid function is essential because lithium can gradually impair both over time. The CANMAT/ISBD guidelines recommend that thyroid and renal function, as well as plasma calcium, be assessed at six months and at least annually thereafter.
For patients on valproate, menstrual history should be assessed periodically in women of reproductive age because of the association between valproate and polycystic ovary syndrome. Liver function and blood counts should be monitored at three-to-six-month intervals during the first year and annually thereafter.
For patients on antipsychotics, metabolic monitoring — weight, glucose, and lipids — should continue annually at minimum, with more frequent checks if abnormalities are detected.
What to Expect at R&K Wellness Group
At R&K Wellness Group, lab orders are not a formality: they are a clinical tool used to provide safer, more effective care. When labs are ordered, the provider will explain what is being tested and why. Lab results are reviewed at follow-up visits and used to inform treatment decisions.
Not every patient will need labs. The decision depends on the clinical situation, the medications being considered, and the patient's medical history. But when labs are indicated, they are an essential part of the treatment process, and not an add-on.
As with all services at R&K Wellness Group, the first appointment is an initial consultation. The consultation does not automatically establish ongoing care. Ongoing services require mutual agreement between the patient and the provider. R&K Wellness Group is not an emergency or crisis service. Patients experiencing a mental health crisis should call 988 (the Suicide and Crisis Lifeline), go to the nearest emergency room, or call 911.
The Bottom Line
Labs in psychiatry are not about checking boxes. They are about answering critical clinical questions: Is there a medical condition driving these symptoms? Is it safe to start this medication? Is the medication at the right level? Is the body tolerating it well over time?
Psychiatric care that ignores the body is incomplete care. Laboratory testing bridges the gap between the mind and the body — and it is one of the ways a psychiatric provider ensures that treatment is not just effective, but safe.
References
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Canadian Network for Mood and Anxiety Treatments ( CANMAT ) and International Society for Bipolar Disorders ( ISBD ) 2018 guidelines for the management of patients with bipolar disorder. Yatham LN, Kennedy SH, Parikh SV, et al. Bipolar Disorders. 2018;20(2):97-170. doi:10.1111/bdi.12609.
The International Society for Bipolar Disorders (ISBD) consensus guidelines for the safety monitoring of bipolar disorder treatments. Ng F, Mammen OK, Wilting I, et al. Bipolar Disorders. 2009;11(6):559-95. doi:10.1111/j.1399-5618.2009.00737.x.
Bipolar Disorder. Carvalho AF, Firth J, Vieta E. The New England Journal of Medicine. 2020;383(1):58-66. doi:10.1056/NEJMra1906193.
A 5-Year Study of Lithium and Valproic Acid Drug Monitoring in Patients With Bipolar Disorders in an Italian Clinical Center. Carli M, Risaliti E, Francomano M, et al. Pharmaceuticals (Basel, Switzerland). 2022;15(1):105. doi:10.3390/ph15010105.
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2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes-2026. American Diabetes Association Professional Practice Committee for Diabetes*. Diabetes Care. 2026;49(Supplement_1):S27-S49. doi:10.2337/dc26-S002.
Management of First-Episode Psychosis and Schizophrenia (SCZ) (2023). Marlene Arias-Reynoso DNP PMHNP-BC, Jennifer L. Bell MD, Pamela Blueford LICSW, et al. Department of Veterans Affairs.