Screening Labs for New Patients: Are They Useful?

Screening Labs for New Patients: Are they UsefulDr. George Lundberg, former editor-in-chief of JAMA and current editor of Medscape General Medicine, once cautioned physicians against the excessive use of routine labs: “The more lab tests that are done, the greater the chance for an abnormal result, whether or not the patient is sick” (see viewarticle/495665).

In psychiatry, we typically order screening labs on new patients for a variety of purposes, including to rule out medical causes of psychiatric symptoms, to record baseline data before prescribing medications that may lead to lab abnormalities, and to screen for general medical problems. What labs should we order for new patients? A literature review yields very little hard data to guide decisions, so what follows is a combination of research based recommendations and common clinical sense.

General Guidelines

1. Before you order any labs, think about what you intend to do about the results. As psychiatrists, we need to be realistic about whether we have kept up on the current general medical literature. There are significant liability issues if you order many labs but are not up to date in the art of interpreting them. Once the numbers are in your chart, you own them, and can be sued for malpractice if you don’t follow up any abnormal values appropriately.

2. Rather than ordering screening labs, it is more important to make sure your patient is receiving appropriate health maintenance care from a primary care physician. National guidelines for adult preventive care are complicated and are updated yearly. For example, from age 21 to 50, current guidelines recommend that all patients should see their PCP every one to three years; after age 50 it should be annual. Depending on variables such as gender, age, and other risk factors, all your patients should be receiving regular screening tests such as breast exams, pelvic exams and pap tests, fecal occult blood tests, testicular and prostate exams, and skin exams for melanoma. The bottom line is: Don’t fool yourself into believing that you are fulfilling the role of a PCP by simply ordering some lab tests.

Brief Research Review and Recommendations

The best reason for psychiatrists to routinely order a battery of tests is to provide a baseline in case you need to prescribe a medication that can cause lab abnormalities. Common psychiatric medications can cause abnormalities in the complete blood count (CBC) (anticonvulsants, some antipsychotics), electrolytes (SSRIs, anticonvulsants), kidney functions tests (lithium), thyroid function tests (lithium), lipids (antipsychotics) and liver function tests (anticonvulsants, some antidepressants). Thus, one can argue that you should order this entire battery of tests just in case your patient ends up on one of these meds.

A more common rationale for ordering baseline labs is to screen for potentially treatable medical conditions that might contribute toward a psychiatric presentation.

There have been very few studies done to evaluate the utility of this practice. The first comprehensive review (Anfinson TJ et al., Gen Hosp Psychiatry 1992;14:248-257) concluded that screening labs often reveal abnormalities in patients who: 1. Are inpatients, particularly in state hospitals and VAs; 2. Have low socioeconomic status; and 3. Have poor outpatient follow-up. In these populations, the medical problems revealed by screening labs were consequences of poor health care, but were unlikely to be causes of psychiatric illness. Such patients require thorough physical exams, review of systems, and lab testing in order to pick up on a variety of medical problems. But studies focusing on general inpatient units, in which high proportions of patients had private insurance, found much lower rates of clinically significant lab findings, ranging from 0.8% to 4%. Synthesizing all the studies, the authors reported that the most useful tests for a limited screen for inpatients were serum glucose, electrolytes, BUN, creatinine, and urinalysis.

A more recent review (Gregory RJ et al., Gen Hosp Psychiatry 2004;26:405- 410) also found low yields of abnormal labs when they were ordered indiscriminately for psychiatric inpatients. Combining the results from eight studies, they reported the following rates of clinically significant lab abnormalities: CBC, 2.2%; urinalysis, 3.1%; electrolytes, 1.7%; thyroid function tests, 2.1%; B-12, 5.7% (this was based primarily on the results from a single study); RPR/VDRL, 0.3%. Looking more closely at some of the subpopulations of these studies, the authors concluded that labs for inpatients should be reserved for those with high pre-test probabilities of having a medical illness, including the elderly, substance users, patients with no prior psychiatric history, and patients who present with clear histories of prior medical problems.

As you can see, the focus of all of these studies is on inpatients, providing little guidance for the majority of psychiatrists, who see primarily outpatients. I found only two studies focusing on outpatients, and both tested the utility of ordering a TSH (thyroid stimulating hormone) in outpatients presenting with major depression. The yield of cases of clinical hypothyroidism was very low. In a series of 200 outpatients with major depression, there were no overt cases of hypothyroidism, and there were 5 (2.6%) cases of “subclinical” hypothyroidism. All patients were treated openly with Prozac, and there was no relationship between response rate and thyroid status (Fava M et al., J Clin Psych 1995 May; 56(5):186-192). In a larger series of 725 geriatric outpatients with depression, only 5 patients (0.7%) had high TSH levels, and patients with elevated TSH did not differ from patients with normal TSH in the severity or symptom pattern of depression (Fraser SA et al., Gen Hosp Psychiatry 2004;26:302-309).

Bottom Line Recommendations for Screening

1. For inpatients or outpatients of low SES and low rate of outpatient medical care: Obtain a medical consultation for health care maintenance evaluation. If this is not available in your setting, do your own physical exam, conduct a careful medical review of systems, and order a full battery of screening tests: CBC, electrolytes, BUN, creatinine, glucose, lipid panel, liver function tests, thyroid function tests, B12, urinalysis. For those at higher risk for STDs, order VDRL.

2. For inpatients of higher SES with private insurance: Obtain medical consultation from patient’s PCP, or if this is not readily available, obtain a list of recent lab results. Get limited screening battery: serum glucose, electrolytes, BUN, creatinine, and urinalysis.

3. For outpatients of higher SES with private insurance: Unless you are planning to start medications that may cause specific lab abnormalities, do not order any labs, and ensure that the patient receives basic recommended health care maintenance visits with a PCP.

TCPR VERDICT: Screening labs: Reserve them for poor inpatients.

Screening Labs for New Patients: Are They Useful?

This article originally appeared in:

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This article was published in print 8/2007 in Volume:Issue 5:8.