Contrast-induced nephropathy (CIN) is a hot topic now in diagnostic imaging, and medicine in general. It’s not as common as is being reported in some studies, and the resultant renal function decline, when it occurs, is often mild and transient, yet the risk of more severe renal dysfunction and potential chronic renal failure is real. It’s a risk that has been treated with respect of late, with new cautious guidelines in place.

The vast majority of CIN cases in the literature involve intra-arterial contrast injections (angiograms) rather than IV administration (CT scans). It’s logical that the kidneys would be exposed to a more concentrated form of the contrast with intra-arterial injection. The risk of nephropathy is markedly increased in patients with pre-existing conditions such as diabetes, chronic renal insufficiency and dehydration. The danger is reduced by improving pre- and post-test hydration, using lower contrast dosage, and using lower-risk contrast media (low osmolar and iso-osmolar contrast vs more risky high-osmolar contrast).

Some studies have identified pre-contrast medications that may further reduce the risk of CIN, such as the antioxidant N-acetylcysteine (NAC), which can be taken orally. But follow-up controlled trials have yet to vindicate early optimism about such medications.

It’s vital for family doctors to include recent renal function data with the requisition for any patient they’re sending for contrast studies. Virtually all requisitions arriving in the diagnostic imaging department for contrast studies are pre-screened by the radiologists to assess risk. In the past, serum creatinine has been the gold standard for renal function monitoring, but today estimated GFR (eGFR) is the lab test of choice.

The current recommendation is that precautions aren’t needed for patients with an eGFR of ≥ 60 mL/min. That’s the criterion we use at our institution. Some studies are now suggesting that a limit of ≥ 40 mL/min can be safely used for IV iodinated contrast administration (such as CT scans), and that the 60 mL/min limit should be reserved for intra-arterial studies (angiography).

The same eGFR limit of 60 mL/min is also used to screen patients prior to MRI gadolinium IV contrast. With MRI contrast, though, the concern is the potential development of nephrogenic systemic fibrosis (NSF), which is a rare disease that’s been linked to MRI contrast media. Symptoms may include systemic manifestations, i.e. fibrosis of the skeletal muscle, bone, lungs, pleura, pericardium, myocardium, kidney, muscle, bone, testes and dura. Results can be quite disabling.