OBJECTIVES: Cardiac surgery can result in renal impairment necessitating hemofiltration (HF; dialysis) which prolongs the length of therapy (LOT), days in the intensive care unit (ICU) and is associated with an overall higher mortality. The decision to initiate HF-therapy is currently made on increased plasma creatinine levels, a relatively late marker (peaking days after a potentially reversible renal dysfunction). The novel urine marker NGAL (neutrophil-gelatinase-associated lipocalin) measures the acute structural damage and identifies the need for HF within hours with high accuracy.  METHODS: Based on data collected in 2005-2009, we prospectively included NGAL in an algorithm to modify the management of HF-therapy in 2010. Changes in incidence of HF and LOT, all costs associated with routine NGAL-testing and ICU stay (direct and indirect) as well as the economic impact were analysed.   RESULTS:   A total of 528 patients were operated with no statistical difference in numbers, case mix, risk scores and outcomes to the previous years. The expected number of patients with HF was 45.3 with an average LOT of 7.7 days (2005-2009). Introduction of NGAL-testing added costs of € 60.00/patient (€ 31.680/year). Although € 2047,50/day could be realized through public health refunding, the fixed associated costs were € 3249,70/patient/day [€ 892,52 for all supplies to operate the HF (Prismaflex, Gambro, Germany) and € 2357,18 for institutional ICU expenditure (incorporating personnel costs)] resulting in a deficit of € 1202,19/day with, and € 751,58 without HF operating. Using the new marker, only 32 patients required treatment with HF for a mean of 5.5 days and earlier initiation (1.1 days) in 2010 (p<0,001). A total of 41.6 days of  treatment in ICU (occupancy) were avoided with savings of € 44.153,16. CONCLUSIONS: Routine NGAL testing and consecutive changes in management reduced the number of HF-therapies, lengths of therapy and ICU stay in our institution and proved to be cost-saving.