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Everything you need to know about Computed Tomography (CT) & CT Scanning

Unique Clinical Scenarios

question1. The patient has sickle cell disease. Can they get IV contrast?
question2. The patient has multiple myeloma. Can they get IV contrast material?
question3. If a patient has thyroid disease is iodinated contrast contraindicated?
question4. If a patient has thyroid cancer is iodinated contrast contraindicated?
question5. If a patient has myathenia gravis should iodinated contrast be used for a chest CT?
question6. If a patient is on glucophage (or other oral diabetes medications) is there an issue with iodinated contrast agents? What is the current rule with oral diabetes drugs? (glucophage)
question7. What patients take glucophage (metformin)?
question8. What is the danger of Metformin and iodinated contrast?
questionBiguanides are known to cause lactic acidosis in patients with a predisposing risk factor. The actual incidence for metformin is, however, quite low and when it has occurred has frequently been in patients with risk factors.
  • Risk Factors for Metformin
  • Renal impairment (delayed excretion of metformin, acidosis). Serum Creatinine >1.3mg/dl for women, >1.4mg/dl for men.
  • Excess alcohol use.
  • Shock: CHF, sepsis, myocardial infarcts, dehydration.
  • Acidosis.
  • Major surgery.
  • Hypoxia, COPD, pneumonia, asthma.
  • Use of iodinated contrast material (stop metformin before study).
  • Stop in-hospitalized patients and substitute insulin until discharge.
  • Cirrhosis.

Intravascular contrast studies with iodinated materials can lead to acute alteration of renal function and have been associated with lactic acidosis in patients receiving Glucophage® (see Contraindications). Therefore, in patients in whom any such study is planned, Glucophage® should be discontinued at the time of or prior to the procedure and withheld for 48 hours subsequent to the procedure and reinstituted only after renal function has been re-evaluated and found to be normal. (Note the requirement to stop metformin 48 hours before the contrast study has been eliminated).

Because metformin (Glucophage®) is eliminated by the kidney through filtration and tubular secretion, impairment of renal function can lead to persistence of metformin and development of lactic acidosis. Approximately 90 percent of the absorbed drug is eliminated by the renal route within the first 24 hours. Withholding the drug for 48 hours after administration of intravascular iodinated contrast material allows metformin to clear and provides an opportunity to assess any alteration in renal function caused by the administered intravascular contrast.

Update on metformin (Glucophage®) therapy and the risk of lactic acidosis: change in FDA-approved package insert. 
Bush WH, Bettmann MA. 
ACR Bulletin 1998; 54(3): 15.

question9. What are the other names for metformin?
question10. What are the current guidelines for patients taking metformin and needing a contrast study?
question11. Is there any problem with using iodinated contrast for CT if a patient is on the cardiac drug Amiodarone?
question12. Can you use iodinated contrast on a patient with suspected or known pheochromocytoma?
question13. If a patient is nursing can she receive IV contrast?
question14. What is our policy for scanning a pregnant patient?
question15. If a CT is done on a pregnant patient and iodinated contrast is used can that affect the fetus?
question16. Who should get baseline serum creatinine levels before CT?
© 1999-2020 Elliot K. Fishman, MD, FACR. All rights reserved.