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===Weight adjustment===
The needed dose is proportional to the ''lean body weight'' of the patient. For contrast CTin obese individuals, this is optimally calculated by the Boer formula, using height and weight of the patient.<ref name="CarusoDe Santis2018">{{cite journal|last1=Caruso|first1=Damiano|last2=De Santis|first2=Domenico|last3=Rivosecchi|first3=Flaminia|last4=Zerunian|first4=Marta|last5=Panvini|first5=Nicola|last6=Montesano|first6=Marta|last7=Biondi|first7=Tommaso|last8=Bellini|first8=Davide|last9=Rengo|first9=Marco|last10=Laghi|first10=Andrea|title=Lean Body Weight-Tailored Iodinated Contrast Injection in Obese Patient: Boer versus James Formula|journal=BioMed Research International|volume=2018|year=2018|pages=1–6|issn=2314-6133|doi=10.1155/2018/8521893}}</ref> Taking this formula, the needed volume of IV contrast from the unadjusted volume given in the table above becomes:*For men: Weight-adjusted volume = Unadjusted volume x ((0.00581 00723 × W) + (0.00381 00474 × H) − 0.274341)*For women: Weight-adjusted volume = Unadjusted volume x ((0.0036 00583 × W) + (0.00676 011 × H) − 01.6912)
, where W is body weight in kilograms and H is body height in centimeters.
'''Hydration''' by drinking or intravenous volume expander, either before or after contract administration, decreases the risk of contrast-induced nephropathy.<ref name="YangHiremath2013">{{cite journal|last1=Yang|first1=Xiaoming|last2=Hiremath|first2=Swapnil|last3=Akbari|first3=Ayub|last4=Shabana|first4=Wael|last5=Fergusson|first5=Dean A.|last6=Knoll|first6=Greg A.|title=Prevention of Contrast-Induced Acute Kidney Injury: Is Simple Oral Hydration Similar To Intravenous? A Systematic Review of the Evidence|journal=PLoS ONE|volume=8|issue=3|year=2013|pages=e60009|issn=1932-6203|doi=10.1371/journal.pone.0060009}}</ref>
==Example==
As a fictional example, an obese 50 year old male has undergone gastric bypass surgery two days before and has now developed abdominal pain and diarrhea. This is an indication for CT with IV (and oral) contrast.<ref name="LevineCarucci2014">{{cite journal|last1=Levine|first1=Marc S.|last2=Carucci|first2=Laura R.|title=Imaging of Bariatric Surgery: Normal Anatomy and Postoperative Complications|journal=Radiology|volume=270|issue=2|year=2014|pages=327–341|issn=0033-8419|doi=10.1148/radiol.13122520}}</ref> GFR is estimated to be 30 ml/min.
Medical records are checked for additional risk factors, finding diabetes. Based on this, it is deemed appropriate to keep a ratio of maximum 1 g iodine/(ml/min of GFR). With the local iodine concentration of 350 mg/ml, the amount that can be given is:
*2.9 ml * 30 = 87 ml
With the local iodine concentration being 350 mg/ml, the weight-unadjusted volume needed for the abdominal CT is 60 ml. The patient weights 120 kg and is 176 cm tall. The weight adjusted volume is thus:
*60ml x ((0.00723 × 120) + (0.00474 × 176) − 0.341) = 82 ml
The contrast that can be given is thus slightly less than is needed. The patient was probably dehydrated from the diarrhea, and may be rehydrated before the exam. In an emergency, the patient may need surgery without a prior CT.
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