Abstract How should we monitor methotrexate therapy in psoriatic patients to avoid hepatic cirrhosis? The standard approach requires liver biopsies after each 1.5 g of methotrexate, in addition to performing liver function tests three to four times per year. In this issue of the Archives, O'Connor and his colleagues1 suggest that we may be able to avoid exposing many of our patients to the risk of morbidity and mortality associated with multiple liver biopsies by using simple and relatively inexpensive liver function tests. They derive a prediction rule for hepatic fibrosis based on the results of these tests. The evaluation of the validity of such a prediction rule involves several basic epidemiologic concepts related to diagnostic testing.2-10 These are reviewed below in the context of predicting hepatic fibrosis with a liver function test. Mentioned below are some general pitfalls in the assessment of test validity, and a discussion of more References 1. O'Connor GT, Olmstead EM, Zug K, et al. Detection of hepatotoxicity associated with methotrexate therapy for psoriasis . Arch Dermatol. 1989;125:1209-1217.Crossref 2. Yerushalmy J. Statistical problems in assessing methods of medical diagnosis with special reference to x-ray techniques . Public Health Rep. 1947;62:1432-1449.Crossref 3. Ransohoff DF, Feinstein AR. Problems of spectrum and bias in evaluating the efficacy of diagnostic tests . N Engl J Med. 1978;299:926-930.Crossref 4. Department of Clinical Epidemiology and Biostatistics, McMaster University. How to read clinical journals, II: to learn about a diagnostic test . Can Med Assoc J. 1981;124:703-710. 5. Griner PF, Mayewski RJ, Mushlin AI, Greenland P. Selection and interpretation of diagnostic tests and procedures: principles and applications . Ann Intern Med. 1981;94:553-600. 6. Sheps SB, Schechter MT. The assessment of diagnostic tests: a survey of current medical research . JAMA. 1984;252:2418-2422.Crossref 7. Hlatky MA, Mark DB, Harrell FE, Lee KL, Califf RM, Pryor DB. Rethinking sensitivity and specificity . Am J Cardiol. 1987; 59:1195-1198.Crossref 8. Tavel ME, Enas NH, Woods JR. Sensitivity and specificity of tests: can the `silent majority' speak? Am J Cardiol. 1987;60:1167-1169.Crossref 9. Begg CB. Biases in the assessment of diagnostic tests . Stat Med. 1987;6:411-423.Crossref 10. Begg CB, McNeil BJ. Assessment of radiologic tests: control of bias and other design considerations . Radiology. 1988;167:565-569.Crossref 11. Swets JA. Measuring the accuracy of diagnostic systems . Science. 1988;240:1285-1293.Crossref 12. Hanley JA, McNeil BJ. The meaning and use of the area under a receiver operating characteristic (ROC) curve . Radiology. 1982;143:29-36.Crossref 13. Wasson JH, Sox HC, Neff RK, Goldman L. Clinical prediction rules: applications and methodological standards . N Engl J Med. 1985;313:793-799.Crossref 14. Lachenbruch PA. Discriminant Analysis . New York, NY: Hefner Press; 1975:25-39. 15. Efron B, Gong G. A leisurely look at the bootstrap, the jackknife, and cross-validation . Am Statistician. 1983;37:36-48.
Archives of Dermatology – American Medical Association
Published: Sep 1, 1989