Intra-rater and inter-rater reliability of ultrasonographic intestinal wall thickness measurements in healthy horses.
Authors: Hansen Tina, Kendall Anna, Finne Rebecca, Law Ellen, Ringdahl Agnes, Nostell Katarina
Journal: Equine veterinary journal
Summary
Ultrasonographic assessment of equine intestinal wall thickness is routine in equine practice, yet the reliability of these measurements has received surprisingly little scrutiny. Hansen and colleagues examined how consistently three operators could measure intestinal wall thickness across six regions (duodenum, caecum, jejunum, and the three colonic segments) in eight healthy horses over three consecutive days, using intra-class correlation coefficients to quantify both within-operator and between-operator reliability. Whilst intra-rater consistency was generally poor (ICC <0.5 for most regions except the duodenum at 0.52), inter-rater reliability varied by location, ranging from poor performance in the duodenum, caecum and jejunum to moderate reliability in the right and left ventral colons and right dorsal colon (ICC 0.5–0.75); importantly, the absolute variation between repeated measurements remained small, with 95% of all measurements falling within a ±1 mm range. The practical implication is valuable: clinicians can confidently treat intestinal wall thickness changes of less than 1 mm as measurement noise rather than true pathological shifts, whilst differences exceeding this threshold warrant clinical attention. Although the study's restriction to healthy animals limits direct application to colic cases or inflammatory conditions, these findings provide an evidence-based framework for interpreting serial ultrasound examinations and establishing when observed changes represent genuine intestinal changes versus operator or technical variation.
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Practical Takeaways
- •Differences of less than 1 mm in intestinal wall thickness measurements between examinations should be considered within normal measurement variability and not interpreted as pathological change
- •Serial ultrasound examinations of intestinal wall thickness remain clinically useful despite moderate inter-observer variation, provided findings are interpreted conservatively
- •When comparing follow-up ultrasound scans to assess intestinal disease progression, only changes ≥1 mm can be confidently attributed to true biological change rather than operator or measurement error
Key Findings
- •Intra-rater ICC ranged from <0.5 to 0.52 across intestinal regions, with duodenum showing the best reliability
- •Inter-rater ICC was <0.5 for duodenum, caecum, and jejunum, but 0.5-0.75 for RDC, RVC, and LVC
- •Standard deviation of repeated measurements was low at 0.33-0.45 mm across all regions
- •95% of all reported measurements fell within a 1 mm range, establishing a practical threshold for distinguishing true changes from measurement variation