A re-evaluation of the scratch test for locating the liver edge

A reliable and accurate estimation of liver size by physical examination is an important aspect of the clinical assessment of a patient. The scratch test uses auscultation to detect the lower liver edge by using the difference in sound transmission through the abdominal cavity over solid and hollow organs. The test is thought to be particularly useful if the abdomen is tense, distended, obese, or very tender. Although the sign is often taught to medical students and residents, the value of the technique for detecting the liver edge has become controversial.

The study was performed in two parts. In the first part, 18 patients undergoing upper abdominal ultrasound as outpatients were randomly selected and the scratch test was performed by two raters independently, followed by ultrasound (USG) as the reference standard. In the second part of the study, the two raters independently performed the scratch test on separate randomly selected patients (15 patients by rater 1, and 16 patients by rater 2), followed by USG.

Agreement between raters on the scratch test was very high, with an intra-class correlation coefficient of 0.97. The agreement between the raters and the USG was 0.37 using Spearman's rho. A Bland -Altman plot indicated that, on average, raters underestimated the distance from the right costal margin to the liver edge by only about 2.4 centimeters compared to USG. This translates into 37% and 54% of raters' estimates falling within 2 and 3 cm of USG estimates. Each unit increase in BMI increased the discrepancy between raters and USG by 0.26 cm (p = 0.012).

The scratch test has very high reproducibility and overall agreement between the scratch test and USG was moderate, with a spearman's rho of 0.37. The accuracy may potentially be improved by using the point of initial sound transmission rather than the point of maximal transmission. We conclude that the scratch test deserves further investigation.