Table 1: Risk factors for development of contrast-induced nephropathy. Patient-related factors Procedure-related factors 3 Modiﬁable Volume depletion Anemia, PCI related blood loss Nephrotoxic drug use Low serum albumin Volume of contrast media Multiple administration of CM within 72 hours Osmolality and ionicity of CM Cardiology Research and Practice Nonmodiﬁable Age Diabetes mellitus with CRF Preexisting renal failure Congestive heart failure Hemodynamic instability Nephrotic syndrome Renal transplant IABP Emergent/primary PCI Intraarterial CM administration CM, contrast media; CRF, chronic renal failure; IABP, intra-aortic balloon pump; PCI, percutaneous coronary intervention. 5.6. Type of Contrast. Another important factor contributing to risk of CIN is the type of contrast used, with osmolality playing the key role. Other diﬀerences in contrast media including ionicity and viscosity may also be involved. Properties of contrast media are listed in Table 2. A meta analysis of 31 trials looking at CIN and osmolarity of contrast used revealed that the incidence of CIN was signiﬁcantly higher with high osmolar contrast use in patients with pre existing renal insuﬃciency. In patients without renal disease it was not signiﬁcantly diﬀerent [41]. This was reconﬁrmed by Rudnick et al. who compared low- osmolar nonionic contrast agent, iohexol, and the high- osmolar ionic contrast agent, diatrizoate, in 1,196 patients undergoing cardiac angiography. They found that acute contrast nephrotoxicity was signiﬁcantly higher in patients receiving diatrizoate. Again, this diﬀerence was limited to patients with previous renal insuﬃciency or renal insuﬃ- ciency combined with diabetes mellitus [42]. The advent of iso-osmolar contrast was further promis- ing. In a randomized, double-blind, prospective, multicenter study, Aspelin et al. compared the nephrotoxic eﬀects of an iso-osmolar, dimeric, nonionic contrast medium, iodixanol, with those of a low-osmolar, nonionic, monomeric con- trast medium, iohexol in a group of 129 diabetic patients with serum creatinine concentrations of 1.5 to 3.5 mg per decilitre, and showed that nephropathy induced by contrast medium may be less likely to develop in high-risk patients when iodixanol is used rather than a low-osmolar, nonionic contrast medium [43]. Another meta-analysis of pooled data of 16 double-blind, randomized, controlled trials from 2727 patients comparing iso-osmolar contrast medium iodixanol with low-osmolar contrast media was conducted [44]. The maximum rise of Serum Creatinine and frequency of CIN were both signiﬁcantly lower in patients using iso-osmolar contrast. This was seen in all patients: renal insuﬃciency patients and in patients with combination of renal insuﬃ- ciency and diabetes mellitus. Independent predictors of CIN included CKD, DM + KD and use of low osmolar contrast media. Two recent trials looked at the incidence of CIN in CKD patients with use of iso-osmolar and low-osmolar contrast agents [45]. In the RECOVER trial, the incidence of CIN was signiﬁcantly lower with iodixanol (7.9%) than with ioxaglate (17.0%; P 1/4 0.021). However, the ICON trial showed no signiﬁcant diﬀerence in incidence of CIN [46]. The controversy continued with the CARE [47] and the NEPHRIC trials with the former showing no diﬀerence in the incidence of contrast-induced nephropathy in CKD patients treated with iopamidol or iodixanol, and the latter revealing iodixanol to be superior to iohexol in patients with CKD and DM [48]. In the most recent multicenter, double-blind, ran- domized, parallel-group ACTIVE trials, 148 patients with moderate-to-severe chronic kidney disease, undergoing contrast-enhanced multidetector computed tomography of the liver, were randomized to either the low-osmolar agent iomeprol-400 or iodixanol-320. The incidence of CIN as well as mean rise in serum creatinine was signiﬁcantly higher in the patient group receiving iodixanol [49]. Generally the use of iso-osmolar contrast agents is safer and leads to lower rates of CIN in patients at high risk of developing acute kidney damage. However, it may not be needed in all patients. An expert consensus on this issue is lacking. Furthermore, the iso-osmolar media generally have higher viscosity than their low-osmolar monomeric counterparts. Hence, these media should be prewarmed before infusion, which markedly lowers the viscosity [50]. 6. Risk Assessment and Scoring Systems Patients usually have a combination of risk factors predis- posing them to CIN after PCI. All scoring systems, therefore, attempt to encompass these risk factors. Bartholomew et al. worked on developing a time insensitive scoring system [51]. Independent variables (with weighted scores) included estimated creatinine clearance <60 mL/min (2), urgent PCI (2), intra-aortic balloon pump use (2), diabetes mellitus