5 Use of the Laboratory CRAIG KAPLAN

Ordering and interpreting diagnostic tests are fundamental skills . Surprisingly, however, evidence indicates that many of us are poorly trained in this vital area. Studies have shown that physicians commonly order more laboratory tests than required, use them for the wrong purposes, and ignore or misinterpret their results . While these errors have obvious implications for the quality of patient care, there are large socioeconomic implications as well . Health care expenditures in the United States in the 1980s exceeded $400 billion yearly, approximately 10% of the gross national product . Of this cost, a significant proportion can be attributed to laboratory tests . In one study of costs incurred during hospitalization, laboratory charges accounted for an average of 26% of the hospital bill . It has been estimated that clinical laboratories account for more than $11 billion in health care resources nationally, of which $3 billion was for clinical chemistries alone! Diagnostic tests obviously add up to significant expenditures. If many of these tests are inappropriate, superfluous, or misinterpreted, then learning how to use the laboratory properly might have significant benefits for both individual patients and the economy as a whole . The term diagnostic test does not refer only to costly "big ticket" imaging or monitoring procedures such as magnetic resonance imaging, computerized axial tomography, electronic fetal monitoring, or cardiac catheterization . It refers in addition to the countless laboratory tests ordered every day on patients, tests such as electrolytes, serum chemistries, coagulation profiles, or complete blood counts . While individually inexpensive, these "little ticket" tests account in the aggregate for as much total health care expenditures as the more expensive items, perhaps more . The rationale behind this chapter is to improve the quality of care you offer to your patients while decreasing its cost. Both aims can be achieved by a rational approach to diagnostic test ordering and interpretation . After reading this chapter, you should have an understanding of the following :