So what is the cut off of BNP ?
When the landmark article on BNP published in The New England Journal of Medicine in July 2002 1, the cutoff point in establishing or excluding the diagnosis of congestive heart failure in patients with acute dyspnea was given at 100 pg per milliliter. But over time we learned that this level probably carries more negative predictive value and there may be a huge gray zone before a definite high BNP value, atleast in critical care setting. This month in Critical Care Medicine 2, Dr. Rana and coll. from Mayo Clinic College of Medicine, Rochester, MN looked into this gray zone. Their conclusion:
"When measured early after the onset of acute pulmonary edema, a BNP level of less than 250 pg/mL supports the diagnosis of acute lung injury. The high rate of cardiac and renal dysfunction in critically ill patients limits the discriminative role of BNP. No level of BNP could completely exclude cardiac dysfunction".
The median time from the onset of pulmonary edema to BNP testing was 3 hrs.
Other interesting findings in the study:
* The predictive value of BNP in the differentiation between ALI and cardiogenic pulmonary edema was comparable with PAOP (when measured) and superior to troponin and echocardiographic determination of ejection fraction. (Not supported by other studies - see related peal below).
*The accuracy of BNP improved if pts with renal failure were excluded.
* BNP levels of more than 950 pg/dL suggest congestive heart failure and BNP levels of less than 250 suggest ALI, the values in between have no diagnostic value.
Related previous pearls:
References: click to get abstract/article
1. Rapid Measurement of B-Type Natriuretic Peptide in the Emergency Diagnosis of Heart Failure - July 18, 2002,N Engl J Med 2002; 347:161-167, Jul 18, 2002
2. B-type natriuretic peptide in the assessment of acute lung injury and cardiogenic pulmonary edema - Critical Care Medicine. 34(7):1941-1946, July 2006.