First 10EM - By Justin Morgenstern - June 8, 2022
The paper: Macdonald DB, Hurrell C, Costa AF, McInnes MDF, O’Malley ME, Barrett B, Brown PA, Clark EG, Hadjivassiliou A, Kirkpatrick IDC, Rempel JL, Jeon PM, Hiremath S. Canadian Association of Radiologists Guidance on Contrast Associated Acute Kidney Injury. Can Assoc Radiol J. 2022 May 24:8465371221083970. doi: 10.1177/08465371221083970. Epub ahead of print. PMID: 35608223 [free full text]
Bottom line
These guidelines provide a reasonable summary of the evidence around IV contrast and kidney injury.
If a CT is urgent, you should never delay the CT out of consideration for renal function.
Contrast is still recommended in patients with severe chronic kidney disease or acute kidney injury if the contrast is required to make an important diagnosis and there is not a reasonable alternative diagnostic test. Therefore, if you know that a contrast CT is the only reasonable test, and you are going to order it no matter what the blood work shows, you should not delay the CT just to see the blood work results. Doing so can only hurt your patient.
The only context that blood work is reasonable prior to CT in the emergency department is if there is a reasonable alternative diagnostic test, and the delay caused by adding blood work will not result in any harm.