Intravenous iodinated contrast media is commonly used to enhance diagnostic yield of computer tomography (CT) scans in clinical medicine. However, the perceived risk of contrast-induced nephropathy (CIN) frequently limits its use. While CIN is often self-limiting, it can cause significant morbidity by prolonging admissions and rendering an at-risk individual dialysis dependent. CIN has long been observed and described in clinical studies. There is ample data on CIN after administration of intraarterial contrast, but evidence is less compelling when it comes to intravenous contrast. Increasing studies have called into question the actual risk of intravenous contrast media. Expert panels are suggesting that the risk could have been overstated, leading to contrast being withheld when indicated. There is paucity of local data on this particular issue. More real world data on the actual incidence and risk factors of AKI will be helpful to clinicians.

The investigators plan to conduct a single center, retrospective study, to determine the incidence and risk factors of post contrast AKI in contrast enhanced CT scans.

A single center, retrospective study will be conducted, looking into all patients who had contrast-enhanced CT scans done in a specified time period. Serum creatinine at baseline and at 48-72 hours post-contrast of the participants will be compared to determine presence of post contrast AKI (PC-AKI). Data on the participants' demographics, comorbidities, laboratory results and use of nephrotoxins will also be captured and analysed.

The primary objective of this study is to determine the incidence of AKI after intravenous contrast administration for contrast enhanced CT scans (CECT). The secondary objective is to identify risk factors of PC-AKI and possibly come up with a risk stratification system that can be utilized in clinical practice. The investigators hypothesize that there is significant risk of acute kidney injury after intravenous contrast media administration, but it lower than that in the setting of intraarterial contrast; and that risk factors of AKI may include: pre existing chronic kidney disease, diabetes, hypertension, proteinuria, use of nephrotoxins, age, increased dose of contrast.

Inclusion Criteria:

1. Underwent one or more CT scan in CGH in the stipulated study period
2. CT scan done as an inpatient or outpatient of CGH
3. Serum creatinine available less than 6 months before scan
4. Serum creatinine available within 1 week after scan

Exclusion Criteria:

1. Age 12 or below
2. Dialysis dependent before scan (dialysis related charge code applied 24 months before scan)
3. Baseline serum creatinine not available
4. Post scan serum creatinine not available

Any patient of an acute care hospital with clinical indications for contrast enchanced CT scans, meeting inclusion and exclusion criteria.