Diagnosing heart failure with natriuretic peptides

In this video, from our Cardiology Lab Essentials course, we'll explore the use of natriuretic peptides (such as BNP and NT-proBNP) in the diagnostic workup of acute and chronic heart failure and identify other conditions that can lead to elevated natriuretic peptide levels.

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[00:00:00] When we talk about natriuretic peptide testing, there are two peptides that are typically measured. One is the B-type natriuretic peptide, BNP for short, the other is the N-terminal fragment of proBNP, NT-proBNP for short. There are several commercially available assays that allow you to test the levels of these peptides and plasma. Although there might be analytical advantages or

[00:00:30] disadvantages between them, major guidelines agree that neither BNP nor NT-proBNP is superior for the diagnosis of heart failure. So, the decision which assay to use is made by the hospital. But when should I order NP testing? The main indication for natriuretic peptide testing is clearly establishing the presence of acute or chronic heart failure. In particular, NPs play an important role in prevention,

[00:01:00] diagnosis, and prognosis of heart failure. Let's first talk about prevention. The role of NPs and incident heart failure is still being evaluated. The first large scale trial showed that testing NPs in asymptomatic patients with cardiovascular risk factors like high blood pressure and diabetes, predicted the future of development of heart failure. Diagnosis of heart failure is by far the strongest attribute of NP testing.

[00:01:30] When diagnosing heart failure, we have to distinguish between acute heart failure and chronic heart failure. Let's begin by looking at acute heart failure. Patients with acute symptoms of heart failure most often present in the emergency department. The main symptom of acute heart failure is dyspnea but dyspnea can have many causes. So, how do you know it's heart failure? Of course, there are many puzzle pieces involved in coming to the right diagnosis. You need to obtain medical history, do a

[00:02:00] physical exam to look for clinical symptoms like edema, and perform imaging studies like echocardiography. And last but not least, it can be very helpful to do labs, to test for natriuretic peptides. Natriuretic peptide tests are known for their high negative predictive value, so that means that NP testing is a super helpful tool to rule out the diagnosis of heart failure. However, NP testing has only a modest positive predictive value so it's not so good at

[00:02:30] ruling in heart failure. Positive results should be seen as an add on supporting other positive diagnostic tests and signs. That being said, natriuretic peptide testing is not ideal in just any situation. The best situation to test for NP is in dyspneic patients in whom the clinician is ambivalent. If heart failure is very likely or very unlikely, NP measurement has no substantial additional benefit. So, how do we

[00:03:00] interpret the results? What are the cutoff levels at which we can either rule out or rule in the diagnosis of heart failure? It is important to remember that BNP and NT-proBNP are two different assays with different reference values, so we have to consider different cutoffs for each. When you measure BNP in your lab, values below 100 pg / mL are good for ruling out heart failure as the cause for your patient's dyspnea,

[00:03:30] while values above 500 indicate existing heart failure. When you measure NT-proBNP, values below 300 pg / mL rule out heart failure as the cause of dyspnea at any age. For NT-proBNP, there are age-related cutoffs in favor of heart failure, 450 for individuals younger than 50 years, 900 between the age of 50 and 75, and 1,800

[00:04:00] for individuals older than 75 years. But what does it mean when the patient's results are in between these cutoff levels, in this grey zone? Well, we can't make a decision based on NPs in these cases. In these cases, we have to rely on other tools like imaging studies in order to make the diagnosis of heart failure. Now that we've talked about acute onset heart failure, how useful is BNP or NT-proBNP

[00:04:30] in suspected chronic heart failure? In this setting, patients will mainly present in an outpatient clinic or other primary care facilities. NP testing should be performed in patients with high pre-test probability of having heart failure; based on the findings from their physical exam, their medical history or conspicuous EKG findings. Again, BNP and NT-proBNP have different cutoffs, when you measure BNP in your lab, values below 35 pg / mL

[00:05:00] are good for ruling out heart failure as the cause for patient's symptoms. If your patient has BNP levels above 35, you should initiate echocardiography to confirm the diagnosis of heart failure. When you measure NT-proBNP, values below 125, rule out heart failure. As with BNP, values above 125 should be followed by an echo, to confirm the diagnosis. These rules apply for heart failure

[00:05:30] with reduced as well as with preserved ventricular function. The European Society of Cardiology goes so far as to recommend that further imaging studies are not needed for non-acute patients with NP levels below the cutoff, since NP levels rule out heart failure very well. That means that not every patient with suspected heart failure necessarily needs an echo. However, the decision for or against imaging studies, lies of course,

[00:06:00] in the hands of the clinician. What about natriuretic peptides and prognosis? Both BNP and NT-proBNP provide prognostic information about heart failure. Several studies have shown that the higher the peptide’s concentration, the greater the risk for adverse outcome and mortality. So, you can see that BNP and NT-proBNP play an important role in acute as well as in chronic heart failure, but are there other reasons for elevated NP levels?

[00:06:30] In addition to heart failure, other processes that stress the heart can also lead to elevated NP levels. This could include conditions like coronary heart disease, valvular heart disease, pericarditis, pulmonary hypertension, renal failure or sepsis. This emphasizes how important it is to not only focus on NP values when diagnosing heart failure but to also use your own clinical judgment

[00:07:00] in order to make the diagnosis. So, what are my take-home messages for you? Well, first, BNP and NT-proBNP are very good lab markers to rule out suspected heart failure. And two, both lab markers can support the diagnosis of heart failure in patients with suggestive clinical symptoms.