Barkun et al identified factors associated with the presence of a common bile duct stone in a patient undergoing a laparoscopic cholecystectomy. The authors are from McGill University in Montreal.
Parameters for a patient with no stone seen in the duct on ultrasonography:
(1) age of the patient in years
(2) serum bilirubin in µmol/L
(3) dilatation of the common bile duct seen on ultrasonography (> 6 mm in diameter)
Age in Years
Serum Bilirubin
Dilated Common Bile Duct
Probability of Stone Seen ERCP
<= 55
<= 30 µmol/L
no
19%
<= 55
<= 30 µmol/L
yes
38%
<= 55
> 30 µmol/L
no
28%
<= 55
> 30 µmol/L
yes
49%
> 55
<= 30 µmol/L
no
38%
> 55
<= 30 µmol/L
yes
61%
> 55
> 30 µmol/L
no
50%
> 55
> 30 µmol/L
yes
72%
The presence of common bile duct stone seen on ultrasonography had a specificity of 90% (not 100%) in Table 2. This may be explained if the category is "suspected or detected" as given on page 35. According to the footnote to Figure 3, the range of probabilities for the above factors ranges from 58% to 94%.
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