It is suspected that 13-15% of individuals with low back pain likely have pain referred from the sacroiliac joint (SIJ). There have been multiple proposed ways to assess for dysfunction in this area, but due to a lack of a diagnostic reference standard, the validity for testing for disorder is unknown. Despite this, the most convincing evidence for the diagnosis of SIJ “pain” is provocation testing. When comparing provocation testing to nerve root blocks to the SIJ, it has been determined that the tests have a sensitivity of 94% and specificity of 78% (when 3+ are positive). The Gillets, standing flexion, long sitting(leg length discrepency) and other previously used palpatory tests have been shown to have poor interexaminer reliability, as well as lack sensitivity and specificity.
Bottom line: When attempting to differentiate pain at the SIJ, use provocation.
You can learn more about how to use these tests here.