Likelihood ratios: getting diagnostic testing into perspective.

In modern medicine, sophisticated laboratory tests and imaging studies are often emphasized at the expense of history and physical examination, rather than complementing clinical assessment. Ancillary testing often fails to advance the diagnostic process, and increases patient risk and the expense of medical care. The relative value of clinical evaluation and technological methods is rarely considered, and the power of the clinical evaluation is therefore underestimated. The likelihood ratio (LR) is a semiquantitative measure of the performance of diagnostic tests which indicates how much a diagnostic procedure modifies the probability of disease, and is calculated from the sensitivity and specificity of the test (or directly from the change in probability associated with the test result). We review the performance of frequently-used tests by their LRs, and compare them to the power of clinical assessment, with clinical cases to illustrate the application of LRs in the diagnostic process. The discriminative power of clinical assessment and ancillary tests is often similar, and the combination of the two greatly increases accuracy in the diagnostic process. Clinical assessment is indeed frequently more informative than current technical modalities. LRs assist in putting the value of testing in proper perspective. Practice in evaluating pre-test probabilities of disease and in the application of LRs should be enhanced in medical training.

[1]  John E. Bennett,et al.  Principles and practice of infectious diseases. Vols 1 and 2. , 1979 .

[2]  W Kirch,et al.  Misdiagnosis at a university hospital in 4 medical eras. , 1996, Medicine.

[3]  I. Ringqvist,et al.  Survival of Medically Treated Patients in the Coronary Artery Surgery Study (CASS) Registry , 1982, Circulation.

[4]  A. Wightman,et al.  A prospective analysis of incidental paranasal sinus abnormalities on CT head scans. , 1994, Clinical otolaryngology and allied sciences.

[5]  W. Huck,et al.  Diagnosis of group A beta-hemolytic Streptococcus using clinical scoring criteria, Directigen 1-2-3 group A streptococcal test, and culture. , 1990, Archives of internal medicine.

[6]  James W. Smith,et al.  Bacterial infections of the colon , 2000, Current treatment options in gastroenterology.

[7]  G. E. Newman,et al.  Imaging of the renal arteries: value of MR angiography. , 1991, AJR. American journal of roentgenology.

[8]  J P Beregi,et al.  [Spiral CT angiography in the diagnosis of central pulmonary embolism: comparison with pulmonary angiography and scintigraphy]. , 1996, Revue des maladies respiratoires.

[9]  T Sherwood,et al.  Evaluation of diagnostic tests. , 1989, Clinical radiology.

[10]  R. Allen,et al.  Clinical spectrum and diagnosis of cobalamin deficiency. , 1990, Blood.

[11]  Our stubborn quest for diagnostic certainty. , 1989, The New England journal of medicine.

[12]  T. Pickering,et al.  Detection of renovascular hypertension. State of the art: 1992. , 1992, Annals of internal medicine.

[13]  M. Borggrefe,et al.  Post-infarction depression and incomplete recovery 6 months after acute myocardial infarction , 1994, The Lancet.

[14]  J. Goodwin,et al.  The importance of clinical skills , 1995, BMJ.

[15]  Interpretation of diagnostic data: 5. How to do it with simple maths. , 1983, Canadian Medical Association journal.

[16]  E W Salzman,et al.  Deep-vein thrombosis. , 1994, The New England journal of medicine.

[17]  L. Calabrese,et al.  Weighted criteria for the diagnosis of systemic lupus erythematosus. , 1984, Archives of internal medicine.

[18]  M. Emond,et al.  Long‐term Survival of Medically Treated Patients in the Coronary Artery Surgery Study (CASS) Registry , 1994, Circulation.

[19]  S. Greenhouse,et al.  The evaluation of diagnostic tests. , 1950, Biometrics.

[20]  B. Zaret,et al.  Nuclear cardiology (1). , 1993, The New England journal of medicine.

[21]  L. Goldman,et al.  The value of the autopsy in three medical eras. , 1983, The New England journal of medicine.

[22]  K. J. Wagner Serum enzyme assays in the diagnosis of acute myocardial infarction , 1987 .

[23]  C. Choi,et al.  Bacterial meningitis. , 1992, Clinics in geriatric medicine.

[24]  J Denollet,et al.  Personality as independent predictor of long-term mortality in patients with coronary heart disease , 1996, The Lancet.

[25]  N. Frasure-smith,et al.  Depression following myocardial infarction. Impact on 6-month survival. , 1993, JAMA.

[26]  S. Walter,et al.  Use of certainty of opinion data to enhance clinical decision making. , 1995, Journal of clinical epidemiology.

[27]  A. Toi,et al.  The evaluation of suspected renal colic: ultrasound scan versus excretory urography. , 1989, Annals of emergency medicine.

[28]  J. Kassirer,et al.  The threshold approach to clinical decision making. , 1980, The New England journal of medicine.