Carnett Sign

Original Editor - Umamah Ejaz
Top Contributors - Umamah Ejaz

Introduction

Muscles of abdominal wall

In May 1926, John Berton Carnett (1890–1988) published a paper titled “Intercostal Neuralgia as a Cause of Abdominal Pain and Tenderness.” He described a two-step bedside maneuver, now known as Carnett's Sign, to help determine whether abdominal pain originates from the abdominal wall or an intra-abdominal lesion.

Purpose

Carnett’s sign is a clinical test used to determine whether abdominal pain originates from the abdominal wall or internal organs. To perform the test:

• The examiner identifies the most painful spot by pressing deeply on the abdomen.
• The patient is asked to tense their abdominal muscles (e.g., by lifting their head or legs), and the examiner presses again on the same spot.
• If the pain persists or worsens during muscle tensing, it suggests the pain originates from the abdominal wall. If the pain decreases or disappears, it points to an internal organ as the source.

Technique

The Carnett test is a valuable clinical tool for assessing whether abdominal pain originates from the abdominal wall or internal organs.

How to Perform:

• The patient lies supine, and the examiner identifies the point of maximal tenderness through deep palpation.
• While maintaining pressure on the tender spot, the patient is instructed to tense their abdominal muscles by either lifting their head and shoulders off the table or raising both legs with knees extended.
• As the abdominal muscles contract, the examiner eases finger pressure, allowing the fingers to rise with the abdomen, and then reapplies firm pressure, optionally with a slight twisting motion.

Interpretation:

• Positive Test: Pain remains constant or worsens when the abdominal muscles are tensed, indicating an abdominal wall source.
• Negative Test: Pain decreases when the abdominal muscles are tensed, suggesting an intra-abdominal or visceral origin.

The folowing video shows how to use this test;

Evidence

Diagnostic Accuracy

The sensitivity and specificity of Carnett's sign have been evaluated in various studies:

Psychogenic Abdominal Pain:

• Positive Likelihood Ratio: 2.91 (95% CI: 2.71–3.13)
• Negative Likelihood Ratio: 0.19 (95% CI: 0.11–0.34)

These values suggest Carnett's sign is effective for identifying and excluding psychogenic abdominal pain.

Abdominal Wall Pain:

• Positive Likelihood Ratio: 2.62 (95% CI: 2.45–2.81)
• Negative Likelihood Ratio: 0.23 (95% CI: 0.13–0.41)

The test demonstrates utility in differentiating abdominal wall pain from intra-abdominal sources.

General Sensitivity and Specificity:

• Sensitivity: 78%
• Specificity: 88%

These metrics highlight the test's reliability in distinguishing between the two types of abdominal pain.

Limitations and Variability

Some studies report lower accuracy. For example, one larger patient series found the sensitivity for abdominal wall pain as low as 1%–5% and specificity between 32%–72%, with a positive likelihood ratio of 0.1. These variations indicate that the diagnostic performance of Carnett's sign can depend on patient populations and clinical settings.

Conclusion

While Carnett's sign is a valuable tool for assessing abdominal pain, its diagnostic accuracy may vary. Clinicians should use it as part of a comprehensive clinical evaluation.