The use of the "range of uncertainty".

Most laboratory tests are hampered by overlap of the population with a disease and the population without the disease. An efficient approach to clinical problem solving is to order tests in sequence and focus on the overlap zone of each test--the "range of uncertainty." Indeed, only cases that fall in that range need further workup. All others will have the suspected diagnosis made or excluded with reasonable confidence and need no further testing. To demonstrate the application of this concept, we correlated the iron saturation test and ferritin levels sequentially with the presence or absence of stainable iron in the bone marrow of 139 patients. This model should be suitable for other laboratory tests; it may decrease the use of the laboratory in clinical decision making and reduce the discomfort and cost of additional tests.