Does measuring natriuretic peptides have a role in patients with chronic kidney disease?
HIGH PEPTIDE LEVELS PREDICT DEATH, HOSPITALIZATION
Both BNP and NT-proBNP are strong predictors of death and cardiac hospitalization in kidney patients.1,4,6
In patients with end-stage renal disease, the risk of cardiovascular disease and death is significantly higher than that in the general population, and BNP has been found to be a valuable prognostic indicator of cardiac disease.7
Multiple studies showed that high levels of natriuretic peptides are associated with a higher risk of death in patients with acute coronary syndrome, independent of traditional cardiovascular risk factors such as electrocardiographic changes and levels of other biomarkers. However, these data were derived from patients with mild renal impairment.2
Apple et al8 compared the prognostic value of NT-proBNP with that of cardiac troponin T in hemodialysis patients who had no symptoms and found that NT-proBNP was more strongly associated with left ventricular systolic dysfunction and subsequent cardiovascular death.
PEPTIDE LEVELS ARE HIGHER IN ANEMIA
A significant number of patients with congestive heart failure have renal insufficiency and low hemoglobin levels, which may increase natriuretic peptide levels. It is unclear why anemia is associated with elevated levels of natriuretic peptides, even in the absence of clinical heart failure and independent of other cardiovascular risk factors.9 Nevertheless, anemia should be taken into consideration and treated effectively when evaluating patients with renal impairment and possible congestive heart failure.
PEPTIDES COMPLEMENT CARDIAC ECHO IN END-STAGE RENAL DISEASE
Numerous studies have found a close association between BNP and NT-proBNP levels and left ventricular mass and systolic function in patients with end-stage renal disease.10,11 Data from the Cardiovascular Risk Extended Evaluation in Dialysis Patients study12 suggest that BNP measurement can be reliably applied in end-stage renal disease to rule out systolic dysfunction and to detect left ventricular hypertrophy, but it has a very low negative predictive value for left ventricular hypertrophy in this patient population: someone with a normal BNP level can still have left ventricular hypertrophy.
In addition, volume status is harder to assess with BNP alone than with echocardiography, and an elevated BNP value is not very specific.13
In essence, both BNP and NT-proBNP can be used to complement echocardiography in evaluating cardiac risk in patients with end-stage renal disease. With additional data, it may be possible in the future to use them as substitutes for echocardiography when managing ventricular abnormalities in patients with end-stage renal disease.
USING SPECIFIC CUT POINTS IN RENAL DISEASE
When evaluating a patient with acute dyspnea and either chronic kidney disease or end-stage renal disease who is receiving dialysis, both BNP and NT-proBNP are affected similarly and necessitate a higher level of interpretation to diagnose decompensated heart failure. Currently, researchers disagree about specific cut points for natriuretic peptides. However, deFilippi and colleagues4 suggested the following cut points for NT-proBNP for diagnosing heart failure in patients of different ages with or without renal impairment:
- Younger than 50 years—450 ng/L
- Age 50 to 75 years—900 ng/L
- Older than 75 years—1,800 ng/L.
A BNP cutoff point of 225 pg/mL can be used for patients with an estimated glomerular filtration rate of less than 60 mL/min/1.73 m2, based on data from the Breathing Not Properly multinational study.14
There is no set cut-point for either BNP or NT-proBNP for predicting death and cardiac hospitalization in renal patients, but abnormally high levels should signal the need to optimize medical management and to monitor more closely.
