With more than 1000 laboratory tests now available, nurse practitioners have many choices to help guide the assessment and treatment of patients. These tests account for about 10% of total health care costs, with estimates that approximately 50% of these studies are ill-chosen, poorly timed, not needed or contribute little to clinical outcome.

With the focus on cost-effective health care, the goal is to have the best outcomes by obtaining the most useful information and avoid wasting resources on tests doomed to be inaccurate or less than helpful. Choosing a focused test rather than a broader panel is also helpful in containing costs. In addition, obtain needed screening tests in a manner that minimizes the risk of a false positive result. Here are a few examples:

• Is "routine" lab testing a thing of the past? Tabas & Vanek (1999) cite a study where a laboratory panel of 23 tests done on well, asymptomatic adults from the general population yielded a new diagnosis in less than 2% and a change in management in less than 0.6%.

• Thyroid disease is found in less than 7% of the general population. However, a high index of suspicion should be maintained in those at particular risk, including in the presence of Down syndrome, elevated triglycerides, autoimmune disease, family history of thyroid disease, in the elderly and those taking lithium and amiodorone. As it is highly sensitive and specific, measurement of thyroid stimulating hormone (sTSH) is the best test for thyroid disease screening. Thyroid tests are often bundled together in a thyroid panel or profile, typically giving results that are not needed in screening purposes, such as a free T4. Likelihood of normal free T4 if TSH is normal is approximately 98%. Danesse (1996) advises that a sTSH obtained every five years in all adults is cost effective. It will detect early thyroid disease and minimize the risks associated with its sequelae such as lipid disorders, altered mental status, and dysrhythmia.

• Diabetic nephropathy is typically first manifested with proteinuria. Microalbuminuria, a marker predictive for the development of proteinuria and diabetic nephropathy, is defined as a urinary excretion rate of 30-300mg/day or >40mg/24 hours. With type 2 DM, obtain a microalbuminuria screen at onset of disease and repeat annually if urine total protein remains negative. If persistent, microalbuminuria treatment includes improving glycemic control and adding a medication that will reduce intraglomerular pressure and promote renal protection such as an ACE inhibitor or an angiotensin receptor blocker (ARB). In the presence of UTI, marked hypertension, episodic hyperglycemia and acute febrile illness, avoid microalbuminuria collection to reduce the rate of false positive tests.

• The Clinical Preventive Guidelines recommend fecal occult blood (FOB) testing x 3 annually starting at age 50. However, if done annually from age 50- 75 years, there is a 45% chance of at least one false positive test, yet the possible reduction of colon cancer death rate by 33%. Factors contributing to false positive FOB include inadequate dietary and medication restriction for 3-5 days prior to the test and allowing the stool to come in contact with chlorine toilet bowel cleaner.

Choosing the right laboratory test, and making sure it is accurate, enhances efficient and cost-effective practice. You can learn more about lab data interpretation in the four-hour audiotape program, Laboratory Data Interpretation: A Case Study Approach. The 1.5 hour audiotape program Laboratory Diagnosis: A Focus on Cost Effectiveness and Clinical Outcomes deals with cost effective lab screening for anemia, renal function, colon cancer and select infectious disease.

References:

Danesse, M. et.al (1996) Screening for mild thyroid failure at the periodic health examination: A decision and cost effectiveness analysis. JAMA.276: 285-292.

Jacobs, D., DeMott, W., Grady, H., Horvat, R., Huestis, D., Kasten, B. (1996) Laboratory Test Handbook, Hudson, OH: LexiComp.

Tabas & Vanek (1999) Is "routine" laboratory testing a thing of the past? Current recommendations regarding screening. Post Graduate Medicine 105 (3) 213-220.

U.S. Preventative Services Task Force (1996) Guide to clinical preventive services (2 ed.) Baltimore: Williams and Wilkins.