A much higher impact of renal function on BNP levels was found by Forfia and associates, who reported fourfold greater BNP levels in patients with impaired renal function (estimated creatinine clearance, < 60 mL/min) compared to patients with normal renal function despite similar PCWP values, cardiac index, and LVEF. Interestingly, BNP was better correlated with PCWP in patients with preserved renal function compared to those with impaired renal function. An effect of renal function on BNP levels was also reported by Cuthbertson et al, who found that patients with a serum creatinine level of > 110 Mmol/L had higher BNP levels (p = 0.02) than those with a serum creatinine level of < 110 Mmol/L. The very recent study by Jefic et al revealed an inverse correlation between BNP level and estimated creatinine clearance. Obviously, even moderate renal failure has a significant impact on BNP levels, a fact that must be taken into account when interpreting BNP levels in ICU patients. read
Diseases of the CNS and BNP: The level of BNP, initially called “brain natriuretic peptide” after its detection in the porcine brain, has been reported to be elevated in patients with subarachnoid hemor-rhage, but also in patients with other diseases of the CNS such as epilepsy and stroke. However, in the study by McLean et al, BNP levels did not differ between 10 patients with neurologic problems, including subarachnoid hemorrhage and cerebral tumors, and those without. In contrast, a recent study revealed that two thirds of 174 patients with ischemic stroke had NT-proBNP values clearly above the normal ranges, whereas elevated cTnI or cTnT levels have been detected in < 10% of patients.
However, a significant relation for any of these biomarkers to morbidity and mortality after stroke has not been found. Elevated BNP levels in patients with subarachnoid hemorrhage have been shown to be associated with the severity of associated vasospasms, but also with measures of myocardial performance including regional wall motion abnormalities, impaired LVEF, diastolic dysfunction, cTnI elevation, and pulmonary edema. The elevation of BNP and NT-BNP levels in patients with pathologies of the CNS have been attributed to high sympathetic outflow or the damage of certain regions of the brain with consecutively impaired regulation of BNP re-lease.