Relationship of Loop Diuretic Dosing and Acute Changes in Renal Function during Hospitalization for Heart Failure.

BACKGROUND Worsening renal function (WRF) during heart failure (HF) hospitalization is an accepted correlate of poor prognosis. Loop diuretics are increasingly being considered as a potential cause of worsened HF outcomes, perhaps via WRF. However, the magnitude of worsening in renal function attributable to loop diuretics has not been quantified. METHODS This was a retrospective cohort study of patients who received care from a large health system and had a primary hospital discharge diagnosis of HF between Jan 1, 2000 and June 30, 2008. Patients with preexisting end-stage renal disease were excluded. Daily creatinine (Cr) measurements, furosemide dosing (only loop diuretic on hospital formulary), and radiocontrast dye studies were collected using administrative data. Day-to-day changes in Cr and MDRD estimated glomerular filtration (eGFR) were calculated. The first Cr or eGFR value during hospitalization or in the emergency department was considered baseline. Generalized estimating equations were used to test the association furosemide exposure over previous 2 days to the daily change in Cr and eGFR. Covariates included undergoing radiocontrast study, age, race, gender, and baseline Cr or eGFR. RESULTS Among 6071 patients who met inclusion criteria there were a total of 20,645 observations. This cohort was 51% female, 68% African American, and baseline Cr was 1.36 mg/dl. Furosemide exposure was associated with an average daily increase in Cr of 0.021 mg/dL and decrease in eGFR of 0.72 ml/min/1.73m2 (per 100 mg furosemide daily, both p<0.001). Over a typical length of stay of 5 days this would amount to a Cr increase of 0.11 mg/dL or decrease in eGFR of 3.6 ml/min/1.73m2. Furosemide exposure accounted for only 0.4% and 0.1% of the variation in Cr and eGFR changes, respectively. Undergoing radiocontrast study, African American race, and higher age were associated with day-to-day creatinine increases (all p<0.01). Reanaysis after classifying furosemide exposure into low (<40mg/day), medium (40-100mg/day), and high (>100mg/day) and censoring patients-days after radiocontrast exposure did not significantly affect the magnitude of the worsening renal function. CONCLUSIONS While loop diuretic exposure is statistically associated with WRF among hospitalized HF patients, the associated magnitude of renal function change is very small, and loop diuretics explain little of the variability in renal function during hospitalization. More important explanatory factors likely exist but remain unidentified.