Canadian Association of Radiologists (CAR) recommends AXR for geriatric and psychiatric patients where an accurate clinical history may not be feasible. 1
Role of AXR in the Diagnostic Workup of Constipation
- Validated scoring systems for diagnosing constipation have poor inter-rater reliability and are not practical for EPs to use.2
- A patient with serious underlying pathology is just as likely to have significant fecal loading on AXR as a patient with constipation. 3
- The reported sensitivity (61-80%) of AXR is poor to moderate. 4
Role of AXR in Non-traumatic Abdominal Pain
- A significant proportion of ED patients who have an AXR go on to receive further imaging (CT or US) – suggesting that EPs are using the AXR as a screening test or because of diagnostic uncertainty. 5-7
- The AXR has a minimal impact in correctly changing the EPs initial diagnosis following a H&P (the AXR only significantly improves the sensitivity in the diagnosis of SBO). 8
- For several disease processes (SBO, LBO, free air, volvulus, urolithiasis, body packers) the sensitivity and specificity are moderate at best. 9-15
- A major flaw in the existing evidence is that we do not know why EPs order AXRs.
Low dose CT scans in the ED
- LDCT has similar sensitivity and specificity as standard dose CT for appendicitis 16,17 and ureteral calculi. 18
- Diagnostic Pitfall: LDCT will pick up high-contrast disease (e.g. ureteral calculi), but may miss low-contrast disease (e.g. pancreatic tumour, organ metastases). 19
- Therefore, LDCT should be used in younger patients (age <50) in whom you have a high pretest probability that they have the diagnosis in question (e.g. appendicitis). It is NOT appropriate for older patients in whom you have a wide differential diagnosis.
- The table below is useful when counseling patients regarding radiation doses for abdominal imaging. 20
Take Home Points
- AXR plays no role in the diagnostic workup of constipation
- Exception: geriatric or psychiatric patients in whom you cannot obtain an accurate history
- The presence of fecal loading on AXR does not rule out significant underlying pathology.
- AXR has a limited role for abdominal pain in the ED
- AXR may be useful in select cases (examples: patient with recurrent SBO, or known radiopaque ureteral calculi).
- Evidence suggests EPs may be ordering AXR’s as either a screening test, or because of diagnostic uncertainly.
- Major evidence gap: we do not know why EP’s actually order AXR’s.
- LDCT protocols have diagnostic pitfalls that EP’s should be aware of
- LDCT is appropriate for younger patients where there is a high pretest probability of a single specific diagnosis.
- LDCT may miss low-contrast disease processes (eg: organ metastases, pancreatic tumours).
Edited by Dr. Shahbaz Syed, 4th year Emergency Medicine resident, University of Ottawa