Psychiatric Lab Workup
last authored: Jan 2011, Craig Meloche
last reviewed: Jan 2011, Michelle Mancell
Introduction
There are many conditions, identifiable by lab investigations, that can cause a host of cognitive, emotional, or behavioural changes. Some important tests include:
TSH (thyroid-stimulating hormone)
TSH can be decreased in hyperthyroidism (e.g., Graves disease, autoimmune thyroiditis, etc), or decreased in hypothyroidism. Hyperthyroidism can result in symptoms of anxiety, mania or psychosis, while hypothyroidism can cause depression or psychosis.
fasting glucose and glycosylated hemoglobin
Very high or low blood glucose levels can be associated with delirium. Also, some atypical antipsychotic agents cause abnormal glucose tolerance and may even lead to the development of diabetes mellitus. For this reason, patients on these drugs often have their fasting glucose followed at regular intervals.
CBC and differential
A CBC includes a white blood cell count (WBC), a differential (types of white blood cells), haemoglobin, and platelet count among other parameters. An increase in WBC as well as a left shift in the differential may indicate an infection or the development of neuroleptic malignant syndrome. Some psychiatric medications also cause leukocytosis or leukopenia. A low haemoglobin may be associated with depression or psychosis. The platelet count may be lowered by some psychiatric medications.
blood urea nitrogen (BUN) and creatinine
BUN and creatinine are indicators of kidney function. Since many drugs are excreted through the kidneys, impairment may alter the pharmacokinetics of psychiatric drugs. Also, elevated levels of urea in the blood can cause lethargy and delirium.
folate and vitamin B12
Folate and B12 levels can be low in people with poor nutrition, especially patients who abuse alcohol. Low levels are associated with dementia, delirium, psychosis, fatigue and personality changes. These may not be done in all patients, but added for those considered at risk for poor nutrition.
liver enzymes (ALT, AST, GGT)
Liver enzymes can be raised by alcohol induced liver disease such as alcoholic cirrhosis as well as other causes. Liver disease resulting in high levels of ammonia can cause hepatic encephalopathy which includes lethargy and delirium. Liver disease which results in lowered plasma protein can cause some drugs to be less protein bound which increases their level of activity including both intended effects and side effects.
triglycerides
Some antipsychotic drugs are associated with the development of hyperlipidemia, which itself is associated with a greater risk of cardiovascular and cerebrovascular disease. Also, patients with schizophrenia are already at higher risk of cardiovascular disease, so lipid levels must be followed at regular intervals.
phosphate
Phosphate levels may be raised or lowered by improper parathyroid function. Phosphate may also be lowered in eating disorders, especially with purging behaviours. Levels may drop quickly in a malnourished person who begins to eat a normal diet again because the body uses large amounts of phosphorus during recovery.
magnesium
Low magnesium levels are associated with agitation, confusion, delirium, convulsions and coma. Levels may be low in alcohol abusing patients.
calcium
Low serum calcium levels can cause depression, delirium, and irritability. High levels are associated with depression, psychosis, and weakness. Low calcium levels may be caused by laxative abuse (some eating disorders) or hypoparathyroidism. High levels may be caused by hyperparathyroidism as well as other conditions.
prolactin
Antipsychotic medications may cause a blockade of the dopamine receptors in the pituitary gland which normally down regulate prolactin production. With this blockade in place, prolactin levels may rise and cause galactorrhea, menstrual irregularities, libido changes and alterations in bone calcium concentrations.
VDRL Screen
A VDRL test is performed in the case of dementia patients. This test is used to detect a syphilis infection. A long standing syphilis infection can cause dementia like symptoms.
urine toxicology
A urine toxicology screen is performed on admission because many substances of abuse can alter a person’s perception or exacerbate a mental illness. Also, substance abuse is a frequent comorbid condition with many psychiatric illnesses.
Resources and References
Kaplan and Saddock’s Comprehensive Textbook of Psychiatry 8th edition.
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