How is contrast-induced nephropathy (CIN) diagnosed?
Generally speaking, CIN is thought of as a more quickly reversible form of ATN: muddy brown casts and tubular epithelial cells can be seen in the urine. You should not see features of glomerulonephritis or AIN (RBC casts or WBC casts) or large urine output a la post-ATN diuresis. The surprise twist is that CIN is associated with a FeNa of <1%, which is more consistent with prerenal physiology. Core IM podcast did a great episode on CIN that discusses that what we know about CIN is largely based on animal models, and so there is much about this condition that remains poorly understood. Importantly, they note that biopsy is not helpful because lesions in CIN are non-specific.
Should I give pre- and post-contrast hydration?
Wyatt et al, in this commentary on the 2017 AMACING trial, a Dutch study looking at about 400 patients with CKD stage III getting contrast and risk of CIN, makes clear that the patient’s pretest probability for CIN, as well as the pretest probability for complications from fluid overload, matter a lot. Patients who have diabetes, hypertension, and obviously, CKD that borders on ESRD, are at higher risk. In addition, patients with ESRD who still make urine could be at risk, and giving contrast could worsen their renal function even more. Age (>60 years) may be associated but it’s not clear.if you’re working in an inpatient setting and have a patient with borderline renal function who is at risk of intra-op hypotension and low risk of flashing/pulmonary edema, it’s probably safer to give fluids. A 500 mL NS/LR bolus 30-60 minutes before/after is adequate.
On the other hand, there is very limited evidence to support yes fluids/no fluids. Previous studies that showed reduced risk of AKI with fluids might have shown this benefit because fluids prevented hypotension and ATN, rather than CIN itself. The PRESERVE trial, published in 2018, did not show differences in mortality, dialysis requirement, or persistent worsened kidney function, or CIN in patients receiving preventive IV sodium bicarbonate, oral acetylcysteine, normal saline, or placebo. But, there is always debate in the renal world…if you have a patient with CHF and an EF of 20%…giving fluids or sodium bicarbonate might not be a great idea.
Does the kind of contrast and procedure matter?
Yes.Interventional studies, like coronary angiography, are higher-risk than diagnostic studies. In addition, according to the Core IM podcast, arterial contrast carries a higher risk of inducing CIN compared to venous contrast, although there are issues with differentiating CIN from atheroembolic showers, selection bias, and lack of control groups in these studies.