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Editor,—Adamek et al(Gut1998;43:680–3) presented data on the performance of magnetic resonance cholangiopancreatography (MRCP) in the diagnosis of suspected bile duct obstruction. They compared it with a gold standard of endoscopic retrograde cholangiopancreatography (ERCP), with or without histology and/or repeated ERCP. They presented derived data suggesting that MRCP performed well in diagnosing abnormalities (sensitivity 89%, specificity 92%, positive predictive value 98%) but they omitted to quote the negative predictive value (NPV) for MRCP, which from their data was 71%.
This low NPV is important. In this case, 29% of negative tests missed an important abnormality, which implies that a negative MRCP is of limited value. However, it should be noted that these data are at variance with others who have quoted,1 or from whose data one can derive,2 much higher NPVs. Clearly, more data on the value of a negative MRCP in specific clinical settings are needed in order to define the indications for this test.
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