Editing CT scan (section)

=== Contrast reactions ===
{{Further|Iodinated contrast#Adverse effects}}
In the United States half of CT scans are [[contrast CT]]s using intravenously injected [[radiocontrast agent]]s.<ref name="Nam2006" /> The most common reactions from these agents are mild, including nausea, vomiting, and an itching rash. Severe life-threatening reactions may rarely occur.<ref name="Contrast2005">{{Cite journal |last=Christiansen C |date=2005-04-15 |title=X-ray contrast media – an overview |journal=Toxicology |volume=209 |issue=2 |pages=185–7 |doi=10.1016/j.tox.2004.12.020 |pmid=15767033|bibcode=2005Toxgy.209..185C }}</ref> Overall reactions occur in 1 to 3% with [[nonionic contrast]] and 4 to 12% of people with [[ionic contrast]].<ref name="Wang2011" /> Skin rashes may appear within a week to 3% of people.<ref name="Contrast2005" />

The old [[radiocontrast agent]]s caused [[anaphylaxis]] in 1% of cases while the newer, low-osmolar agents cause reactions in 0.01–0.04% of cases.<ref name="Contrast2005" /><ref name="Drug01">{{Cite journal |vauthors=Drain KL, Volcheck GW |year=2001 |title=Preventing and managing drug-induced anaphylaxis |journal=Drug Safety |volume=24 |issue=11 |pages=843–53 |doi=10.2165/00002018-200124110-00005 |pmid=11665871 |s2cid=24840296}}</ref> Death occurs in about 2 to 30 people per 1,000,000 administrations, with newer agents being safer.<ref name="Wang2011">{{Cite journal |vauthors=Wang H, Wang HS, Liu ZP |date=October 2011 |title=Agents that induce pseudo-allergic reaction |journal=Drug Discov Ther |volume=5 |issue=5 |pages=211–9 |doi=10.5582/ddt.2011.v5.5.211 |pmid=22466368 |s2cid=19001357|doi-access=free }}</ref><ref>{{Cite book |url=https://books.google.com/books?id=bEvnfm7V-LIC&pg=PA187 |title=Anaphylaxis and hypersensitivity reactions |date=2010-12-09 |publisher=Humana Press |isbn=978-1-60327-950-5 |editor-last=Castells |editor-first=Mariana C. |location=New York |page=187}}</ref>
There is a higher risk of mortality in those who are female, elderly or in poor health, usually secondary to either anaphylaxis or [[acute kidney injury]].<ref name="Nam2006">{{Cite journal |vauthors=Namasivayam S, Kalra MK, Torres WE, Small WC |date=Jul 2006 |title=Adverse reactions to intravenous iodinated contrast media: a primer for radiologists |journal=Emergency Radiology |volume=12 |issue=5 |pages=210–5 |doi=10.1007/s10140-006-0488-6 |pmid=16688432 |s2cid=28223134}}</ref>

The contrast agent may induce [[contrast-induced nephropathy]].<ref name="Contrast2009">{{Cite journal |vauthors=Hasebroock KM, Serkova NJ |date=April 2009 |title=Toxicity of MRI and CT contrast agents |journal=Expert Opinion on Drug Metabolism & Toxicology |volume=5 |issue=4 |pages=403–16 |doi=10.1517/17425250902873796 |pmid=19368492 |s2cid=72557671}}</ref> This occurs in 2 to 7% of people who receive these agents, with greater risk in those who have preexisting [[kidney failure]],<ref name="Contrast2009" /> preexisting [[diabetes mellitus|diabetes]], or reduced intravascular volume. People with mild kidney impairment are usually advised to ensure full hydration for several hours before and after the injection. For moderate kidney failure, the use of [[iodinated contrast]] should be avoided; this may mean using an alternative technique instead of CT. Those with severe [[kidney failure]] requiring [[Kidney dialysis|dialysis]] require less strict precautions, as their kidneys have so little function remaining that any further damage would not be noticeable and the dialysis will remove the contrast agent; it is normally recommended, however, to arrange dialysis as soon as possible following contrast administration to minimize any adverse effects of the contrast.

In addition to the use of intravenous contrast, orally administered contrast agents are frequently used when examining the abdomen.<ref>{{Cite journal |last1=Rawson |first1=James V. |last2=Pelletier |first2=Allen L. |date=2013-09-01 |title=When to Order Contrast-Enhanced CT |url=https://www.aafp.org/afp/2013/0901/p312.html |journal=American Family Physician |volume=88 |issue=5 |pages=312–316 |issn=0002-838X |pmid=24010394}}</ref> These are frequently the same as the intravenous contrast agents, merely diluted to approximately 10% of the concentration. However, oral alternatives to iodinated contrast exist, such as very dilute (0.5–1% w/v) [[barium sulfate]] suspensions. Dilute barium sulfate has the advantage that it does not cause allergic-type reactions or kidney failure, but cannot be used in patients with suspected bowel perforation or suspected bowel injury, as leakage of barium sulfate from damaged bowel can cause fatal [[peritonitis]].<ref>{{Cite book |last1=Thomsen |first1=Henrik S. |url=https://books.google.com/books?id=Bun1CAAAQBAJ&q=intravenous+contrast+in+ct |title=Trends in Contrast Media |last2=Muller |first2=Robert N. |last3=Mattrey |first3=Robert F. |date=2012-12-06 |publisher=Springer Science & Business Media |isbn=978-3-642-59814-2}}</ref>

Side effects from [[contrast agent]]s, administered [[Intravenous therapy|intravenously]] in some CT scans, might impair [[kidney]] performance in patients with [[kidney disease]], although this risk is now believed to be lower than previously thought.<ref>{{Cite journal |last=Davenport |first=Matthew |year=2020 |title=Use of Intravenous Iodinated Contrast Media in Patients with Kidney Disease: Consensus Statements from the American College of Radiology and the National Kidney Foundation |journal=Radiology |volume=294 |issue=3 |pages=660–668 |doi=10.1148/radiol.2019192094 |pmid=31961246 |doi-access=free}}</ref><ref name="Contrast2009" />