4. Use of diagnostic tests, including psychological and neuropsychological tests

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Laboratory tests are included in a psychiatric evaluation when they are necessary to establish or exclude a diagnosis, to aid in the choice of treatment, or to monitor treatment effects or side effects (16, 133–144). When laboratory tests are obtained, relevant test results are documented in the evaluation, with their importance for diagnosis and treatment indicated in the clinical formulation or treatment plan.

Diagnostic tests used during a psychiatric evaluation include those that do the following:

  1. Detect or rule out the presence of a disorder or condition that has treatment consequences. Examples include urine screens for substance use disorders, neuropsychological tests to ascertain the presence of a learning disability, and brain imaging tests to ascertain the presence of a structural neurological abnormality.

  2. Determine the relative safety and appropriate dose of potential alternative treatments. For example, tests of hematological, thyroid, renal, and cardiac function in a patient with bipolar disorder may be needed to help the clinician choose among available mood-stabilizing medications (145), or evaluation of cardiac or pulmonary function may be important in determining a patient's medical status prior to electroconvulsive therapy (146).

  3. Provide baseline measurements before instituting treatment, with subsequent measurements used to assess for effects of treatment. For example, baseline and follow-up electrocardiograms may be required to identify effects of antipsychotic or tricyclic antidepressant medications on cardiac conduction, whereas baseline and follow-up glucose levels and lipid panels may be required to identify effects of second-generation antipsychotic agents.

  4. Monitor blood levels of medications when indicated (e.g., for effectiveness, toxicity, or adherence).

Under each of these circumstances, the potential utility of a test will be determined by multiple interrelated factors, including the following:

  1. The likelihood that an individual from a population of similar patients (e.g., of similar age, gender, treatment setting) would have the condition. This probability is also referred to as the prevalence of the condition in that population. In general, conditions that are more prevalent in the population are more likely to be correctly identified by use of a diagnostic test. In the context of obtaining baseline measurements, the likely prevalence of the condition at a later date may also be relevant.

  2. The probabilities that the test will correctly detect a condition that is present (true positive), incorrectly identify a condition as present when it is not (false positive), correctly identify a condition as absent (true negative), or incorrectly identify a condition as absent when it is actually present (false negative). Although information about these probabilities is available for many tests, the key point to consider in clinical practice is that false negative and false positive test results do occur. Furthermore, incorrect identification of a condition can result in unnecessary and potentially detrimental evaluations and interventions; incorrectly viewing a condition as absent can lead to other crucial signs and symptoms of the condition being ignored.

  3. The treatment implications of the test results. Obviously, a test will be of benefit if it correctly detects a previously unidentified and treatable condition. However, the treatment implications may be nil if the test correctly detects a condition that is already known to be present on the basis of clinical examination or history or if it correctly detects a benign or incidental condition that leads to further unnecessary testing with no beneficial effect on treatment.

Given the wide range of clinical situations evaluated by psychiatrists, there are no specific guidelines about which tests should be "routinely" done. It is important to have a clear rationale for the ordering of tests (12, 23, 26), and each patient should be considered individually. Nevertheless, some general principles may aid in deciding on particular diagnostic assessments. For example, tests may be ordered on the basis of the setting (e.g., some patients seen in emergency departments may be at increased risk for certain conditions that warrant diagnostic tests), the clinical presentation (e.g., certain tests are warranted for patients with new onset of delirium), or the potential treatments (e.g., patients may need certain tests before initiation of lithium therapy). For tests that require the patient's participation, factors such as language, education level, intelligence, culture, and level of alertness can affect the testing process and may influence the choice of diagnostic approaches. Patient preferences are also important to consider. Furthermore, the potential benefits of identifying and treating a particular condition need to be weighed against the costs (e.g., time, money, physical pain, emotional stress) of indiscriminate testing.

More detail on the use of laboratory testing to aid in diagnosis and to guide treatment is provided in APA practice guidelines for specific disorders. Table 4 provides examples of and general indications for tests that may be indicated depending on the status of the patient.


Table 4. Tests That May Be Indicated as Part of a Psychiatric Evaluation

Table Reference Number
Table 4. Tests That May Be Indicated as Part of a Psychiatric Evaluation

Neuropsychological testing has a broad range of application, but the decision to order neuropsychological testing for an individual patient remains a matter of clinical judgment (147). Neuropsychological testing may be requested when cognitive deficits are suspected or there is a need to grade for severity or progression of deficits over time. In addition, neuropsychological testing can be helpful in distinguishing between cognitive disorders and malingering or factitious disorders. When patients present later in life with the new onset of psychosis or mood disorder accompanied by cognitive deficits, neuropsychological testing may also be helpful in distinguishing dementia from other psychiatric syndromes. In research studies, typical patterns of cognitive deficits have been identified in a variety of psychiatric disorders, including Alzheimer's disease (148), schizophrenia (149–151), bipolar disorder (152–156), major depressive disorder (157–160), and autism (161, 162). Findings have highlighted the fact that cognitive deficits and associated impairment of social and occupational functioning may persist despite successful treatment of other core symptoms of an illness. For example, executive dysfunction may persist in otherwise responsive depression (163), and working memory may remain impaired in schizophrenia independent of response of positive and negative symptoms (149, 164). Thus, for some patients, a better understanding of persistent neuropsychological impairments can aid in treatment and vocational planning.

Table Reference Number
Table 4. Tests That May Be Indicated as Part of a Psychiatric Evaluation


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