The study aims to recruit 156 (54 Acute Kidney Injury (AKI);102 non-AKI) patients undergoing Cardio pulmonary bypass (CPB) surgery, including those with Chronic Kidney Disease (CKD) and multiple co-morbidities. Urine and blood samples collected pre-operatively and then 0, 3, 6 and 18 hours post-CPB will be stored at -80oC until batch analysed for NGAL using the Abbott and BioPorto assays. AKI - defined as a ≥50% rise in serum creatinine (SCr) over baseline, or the requirement for renal replacement therapy (RRT). SCr will be measured pre-operatively (baseline), then 12 hourly for the first 48 hrs post-CPB and thereafter 24 hourly for 5 days. Clinical data collected will include patient demographics, co-morbidities, drug history, pre-operative renal function, surgery details (type, length, CPB time etc.), length of Intensive treatment unit and hospital stay and post-operative complications. Data will then be analysed comparing the two NGAL tests to find out which is superior, whether it is better to use blood or urine and to define optimal NGAL cut-offs and sample timing for predicting AKI. Both the Abbott and BioPorto assays will subject to a laboratory method evaluation prior to the analysis of any patient specimens in order to verify that their performance is acceptable and meets the manufacturer's claims. This will involve measuring the standard parameters used to assess laboratory assay performance e.g. imprecision (reproducibility), linearity, recovery and method comparison etc.