Users' Guides to the Medical Literature: II. How to Use an Article About Therapy or Prevention A. Are the Results of the Study Valid?

CLINICAL SCENARIO You are working as an internal medicine resident in a rheumatology rotation and are seeing a 19-year-old woman who has had systemic lupus erythematosus diagnosed on the basis of a characteristic skin rash, arthritis, and renal disease. A renal biopsy has shown diffuse proliferative nephritis. A year ago her creatinine level was 140 μmol/L, 6 months ago it was 180 μmol/L, and in a blood sample taken a week before this clinic visit, 220 μmol/L. Over the last year she has been taking prednisone, and over the last 6 months, cyclophosphamide, both in appropriate doses.You are distressed by the rising creatinine level and the rheumatology fellow with whom you discuss the problem suggests that you contact the hematology service to consider a trial of plasmapheresis. The fellow states that plasmapheresis is effective in reducing the level of the antibodies responsible for the nephritis and cites a number