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Intravascular iodinated contrast administration has become crucial to modern medicine. Currently it is estimated that over 250 million injections are given each year worldwide during medical scans and interventions. An acute predefined increase in serum creatinine is considered an indicator of acute kidney injury (AKI). When such an acute increase in serum creatinine occurs within 5 days post-contrast in absence of another aetiology, it is assumed to be iodinated contrast administration induced acute kidney injury. For over 50 years now, acute kidney injury caused by intravascular administration of iodinated contrast material has been considered a leading cause of hospital-acquired renal failure. Contrast has been withheld in fear of kidney injury with misdiagnoses and delayed appropriate patient management as a result. Since 2018, it is now widely accepted that only patients with eGFR <30 mL/min/1.73m2 are at risk of renal injury after intravascular iodinated contrast material injection. However, no study to date has been able to distinguish acute kidney injury caused by iodinated contrast administration from that for which no causal link is established, and it is unsure a causal relationship exists. There are several studies, in attempts to evaluate the causal relationship between contrast exposure and nephrotoxicity, that found fluctuations in absence of contrast similar to those considered to be contrast-induced acute kidney injury. Similarly, it is unsure whether longer-term negative outcomes are inherent to the population studied or a result of contrast administration. However, most of these studies are observational and retrospective in nature. The issue with retrospective studies is that they often cannot control for confounders and therefore cannot give us causation, only association. On the other hand, prospective randomized controlled trials comparing intravascular iodinated contrast administration to no contrast are unlikely given evident ethical issues. The current prospective observational study proposes to use intra-patient comparisons of peak change in renal function during periods in absence of- and with contrast to elucidate the relationship between renal function and contrast administration in this population.

The current prospective observational study proposes to use intra-patient comparisons of peak changes in renal function (serum creatinine) in absence of- and post- intravascular iodinated contrast administration, to elucidate the relationship between renal function and contrast administration in elective patients with eGFR <30 mL/min/1.73m2. The effects of contrast administration on risk of 1-month dialysis and mortality will also be evaluated.

Daily serum creatinine assays will be done 1. during 5 days before contrast (= in absence of contrast), 2. during 5 days after contrast (= post-contrast), and 3. during 5 days at 1-month post contrast (= 1-month post contrast in absence of contrast). Baseline serum creatinine values will be obtained on the day before each 5-day series.

Relevant baseline characteristics of patients will be reported to enable a detailed description of the study population. To explore whether the magnitude of the mean difference in peak change in serum creatinine before and after contrast administration depends on other factors, pre-planned subgroup analyses will be performed. To enable subgroup analyses, data will be collected on 1) prophylactic hydration (yes vs no); 2) administration route (intra-arterial versus intravenous contrast administration); 3) contrast volume (high vs low) and 4) comorbidity (presence vs absence of diabetes).

Inclusion Criteria:

• eGFR <30 mL/min/1.73m2 in absence of dialysis
• referred for an elective procedure with intravascular administration of iodinated contrast material at Maastricht UMC+

Exclusion Criteria:

• age <18 years
• dialysis or pre-dialysis
• intravascular contrast administration <30 days before the first baseline measurement
• emergency or intensive care status
• inability to complete follow-up

Patients with eGFR <30 mL/min/1.73m2 in absence of dialysis referred for an elective procedure with intravascular administration of iodinated contrast material at Maastricht UMC+ are eligible for inclusion.