GASTROENTEROLOGY 2007
DIAGNOSTIC TEST UNIT 2
MRCP
Objectives:
1. To learn to critique and use the results of a diagnostic test article in clinical practice.
2. To learn techniques for educating GI fellows about critical appraisal of a diagnostic test
article. This involves:
a) determining whether the results are valid
b) interpreting the results
c) applying the results to your practice
Clinical Scenario:
A 45-year-old woman presents with recurrent right upper quadrant pain. The patient denies
any significant past medical history, except for an anaphylactic reaction to IV contrast. Physical
examination is unremarkable, except for pain to palpation in the RUQ. Vital signs are normal,
and the patient is afebrile. Lipase, amylase, transaminases, and cbc are normal. RUQ u/s
reveals cholelithiasis. The patient is referred for surgical evaluation and scheduled for
cholecystectomy.
One day prior to surgery, baseline laboratory studies reveal mildly elevated transaminases: AST
= 90 u/l (nl < 49), ALT = 75 u/l (nl < 54). Repeat RUQ u/s reveals the CBD to be 8 mm in
diameter and choledocholithiasis cannot be excluded with certainty. An intra-operative
cholangiogram is planned to rule out choledocholithiasis. However, the patient refuses to
allow an intra-operative cholangiogram because her previous anaphylactic reaction to IV
contrast “nearly killed me!” You decide to perform a magnetic resonance cholangiogram,
which is negative for choledocholithiasis.
GASTROENTEROLOGY 2007
Questions:
1. Are the study designs valid?
2. Was this diagnostic test necessary?
3. What are the likelihood ratios for choledocholithiasis with a positive and negative MRC?
4. What is the post-test probability of choledocholithiasis in this patient?
5. Based on this post-test probability, should you try to convince her to undergo intra-op
cholangiogram (with appropriate pre-treatment to reduce the risk of anaphylaxis)?
Enclosed Materials:
1. Guyatt GH, Rennie D, Editors, The Evidence-Based Medicine Working Group. Users'
Guides to the Medical Literature: A Manual for Evidence-Based Clinical Practice. AMA Press,
Chicago, 2002, Chapter 1C2.
2. Taylor ACF, Little AF, Hennessy OF et al. Prospective assessment of magnetic resonance
cholangiopancreatography for noninvasive imaging of the biliary tree. Gastrointest Endosc
2002;55:17-22. (paper to be appraised)
3. Chan YL, Chan ACW, Lam WWM, et al. Choledocholithiasis: comparison of MR
cholangiography and endoscopic retrograde cholangiography. Radiology 1996;200:85-9.
(paper to be appraised)
4. Schoenfeld P, Guyatt GH, Hamilton F et al. An evidence-based approach to
gastroenterology diagnosis. Gastroenterology 1999;116:1230-7. (accompanying guide to the
critical appraisal of a paper on diagnostic test)
5. Worksheet for evaluating an article on diagnostic test.