When to Order Contrast-Enhanced CT

1 when to Order Contrast-Enhanced CT. JAMES V. RAWSON, MD, and ALLEN L. PELLETIER, MD. Medical College of Georgia at Georgia Health Sciences University, Augusta, Georgia Family physicians often must determine the most appropriate diagnostic tests to Order for their patients. It is essential to know the types of contrast agents, their risks, contraindica- tions, and common clinical scenarios in which Contrast-Enhanced computed tomography is appropriate. Many types of contrast agents can be used in computed tomography: oral, intra- venous, rectal, and intrathecal.

2 The choice of contrast agent depends on route of administra- tion, desired tissue differentiation, and suspected diagnosis. Possible contraindications for using intravenous contrast agents during computed tomography include a history of reac- tions to contrast agents, pregnancy, radioactive iodine treatment for thyroid disease, metfor- min use, and chronic or acutely worsening renal disease. The American College of Radiology Appropriateness Criteria is a useful online resource. Clear communication between the phy- sician and radiologist is essential for obtaining the most appropriate study at the lowest cost and risk to the patient.

3 (Am Fam Physician. 2013;88(5):312-316. Copyright 2013 American Academy of Family Physicians.). R. See related editorial ecent estimates place the number an artifact and obscures pathology. Different . on page 294. of computed tomography (CT) imaging modalities require different con- CME This clinical content scans performed annually in the centrations of contrast for optimal detection conforms to AAFP criteria United States at approximately of pathology. In general, oral contrast is used for continuing medical education (CME).

4 See CME. 70 Given the cost and radiation for most abdominal and pelvic CT scans Quiz on page 302. exposure, it is critical that CT is appropri- unless there is no suspicion of bowel pathol- ate and performed with optimal technique. ogy ( , noncontrast CT to detect kidney Author disclosure: No rel- evant financial affiliations. The decision to Order Contrast-Enhanced stones) or when administration would delay CT is based on the clinical question being a diagnosis in the trauma setting. asked. contrast agents are used to differ- The concentration of barium used for flu- entiate between organs and improve lesion oroscopy is more than 20 times that of the detection and characterization.

5 The type typical oral contrast suspension for CT. For of contrast agent and route of administra- example, the barium concentration from an tion can increase the diagnostic yield of the upper gastrointestinal series or an enema study ordered. will produce an artifact on abdominal CT. because it is significantly more concentrated Types of contrast Agents than bowel contrast agents used for CT. Bar- The most common contrast agents used with ium enemas are also given after abdominal CT imaging are barium- and iodine-based.

6 CT to allow time for the less-dense barium The specific agent and route of adminis- to leave the colon. Barium suspension from tration are based on clinical indications fluoroscopy or CT will not produce an arti- and patient factors. Clear communication fact on abdominal magnetic resonance between the physician and radiologist is imaging. Barium suspensions are not neph- essential for obtaining the most appropriate rotoxic and can be used safely in patients study at the lowest cost and risk to the patient.

7 With renal failure. Water-soluble, iodine-based contrast agents ORAL contrast can also be given orally. They are used for Oral contrast agents are barium- or iodine- bowel opacification and are not nephrotoxic. based and are used for bowel opacification. As with barium agents, they must be diluted The concentration of barium determines for CT compared with the concentrations whether it enhances the diagnosis or causes used in fluoroscopy. Because there is a risk of Downloaded from the American Family Physician Web site at Copyright 2013 American Academy of Family Physicians.

8 For the private, noncommer- 312 American Family cial use of one Physician individual user of the Web site. All other rights reserved. Volume Contact for copyright 88, Number questions 5 September . and/or permission requests. 1, 2013. Contrast-Enhanced CT. SORT: KEY RECOMMENDATIONS FOR PRACTICE. Evidence Clinical recommendation rating Reference A baseline serum creatinine level should be obtained up to one month before administration C 7. of intravenous contrast agents in patients with suspected renal insufficiency.

9 Premedication with antihistamines and corticosteroids is recommended in patients with C 7. a history of mild to moderate reactions to intravenous contrast agents. In patients with normal renal function, repeat measurement of serum creatinine is not C 7. recommended after outpatient administration of intravenous contrast agents. A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series.

10 For information about the SORT evidence rating system, go to aspiration-induced pulmonary edema with concentrated cross-reactivity between shellfish and iodinated con- iodine-based contrast agents, patients must be carefully trast. However, patients with a documented anaphylactic selected. Oral contrast can be administered through a reaction to any medication are at higher risk of a reaction nasogastric tube to minimize the risk of aspiration. to iodinated ,10. Many centers screen outpatients with suspected renal RECTAL contrast insufficiency by measuring serum creatinine one month Rectal contrast can be used in patients with a suspected before administration of contrast agents.