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Diagnosis

Chest radiographs and BNP levels provided complementary information beyond clinical findings for diagnosing heart failure

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ACP J Club. 2004 Sep-Oct;141:48. doi:10.7326/ACPJC-2004-141-2-048


Clinical Impact Ratings

GIM/FP/GP: 6 stars

Hospitalists: 7 stars

Cardiology: 5 stars

Pulmonology: 5 stars


Source Citation

Knudsen CW, Omland T, Clopton P, et al. Diagnostic value of B-type natriuretic peptide and chest radiographic findings in patients with acute dyspnea. Am J Med. 2004;116:363-8. [PubMed ID: 15006584]


Abstract

Question

In patients with acute dyspnea, how do chest radiographic findings and circulating B-type natriuretic peptide (BNP) levels compare for diagnosing heart failure (HF)?

Methods

Design: Blinded comparison of chest radiographs and BNP levels with confirmatory clinical diagnosis.

Setting: 5 teaching hospitals in the United States and 2 in Europe.

Patients: 880 patients (mean age 64 y, 55% men) presenting to the emergency department (ED) with a principal complaint of shortness of breath (either the sudden onset of dyspnea with no history of chronic dyspnea or an increase in the severity of chronic dyspnea); and had complete information on BNP, historical, clinical, and electrocardiographic data, and chest radiographic findings. Patients with dyspnea not caused by HF (e.g., stabbing injuries, trauma, and pneumothorax) were excluded.

Description of tests: Chest radiographs were obtained in the ED, and the presence of cardiomegaly, cephalization, interstitial edema, alveolar edema, pleural effusion, hyperinflated lungs, and pneumonic infiltrates, as interpreted by a radiologist, was recorded. During initial evaluation, BNP levels were measured using the Triage BNP test (Biosite Diagnostics, San Diego, CA, USA)—a fluorescence immunoassay for the quantitative determination of BNP in whole blood and plasma specimens. BNP levels were analyzed within 4 hours or were centrifuged, frozen, and analyzed 1 to 2 days later.

Diagnostic standard: About 30 days after the ED visit, the results of electrocardiography, chest radiography, echocardiography, clinical test results, consultations, and medical record information were used by 2 independent cardiologists to categorize cases as those caused by acute HF or those having noncardiac causes.

Outcomes: Sensitivity, specificity, and positive and negative likelihood ratios for the diagnosis of acute HF.

Main results

447 of 880 patients (51%) had a final diagnosis of acute HF. Of these, 90% had BNP levels ≥ 100 pg/mL. 576 of 880 patients (66%) fulfilled the Framingham criteria for HF. Sensitivity, specificity, and positive and negative likelihood ratios for radiographic findings and cutpoints of BNP levels at ≥ 100, 200, and 300 pg/mL are in the Table. In a multivariate analysis, additional information beyond the clinical predictors of acute HF was provided by BNP at a cutpoint of ≥ 100 pg/mL (odds ratio [OR] 12.3, 95% CI 7.4 to 20.4) and chest radiographic variables of cardiomegaly (OR 2.3, CI 1.4 to 3.7), cephalization (OR 6.4, CI 3.3 to 12.5), and interstitial edema (OR 7.0, CI 2.9 to 17).

Conclusion

In patients with acute dyspnea, chest radiographic variables and circulating B-type natriuretic peptide levels provided complementary diagnostic information beyond clinical predictors for diagnosing heart failure.

Source of funding: Biosite Diagnostics.

For correspondence: Dr. T. Omland, University of Oslo, Oslo, Norway. E-mail torbjorn.omland@klinmed.uio.no.


Table. Diagnostic characteristics of chest radiographic findings and B-type natriuretic peptide (BNP) levels for detecting heart failure*

Tests Sensitivity (95% CI) Specificity (CI) +LR −LR
Cardiomegaly 79% (75 to 83) 80% (76 to 84) 3.98 0.26
Cephalization 41% (37 to 46) 96% (93 to 97) 9.41 0.61
Interstitial edema 27% (23 to 31) 98% (96 to 99) 12.67 0.72
BNP (pg/mL)
≥ 100 90% (86 to 92) 75% (71 to 79) 3.66 0.14
≥ 200 80% (76 to 84) 87% (83 to 90) 6.08 0.23
≥ 300 71% (67 to 75) 90% (87 to 93) 7.18 0.32

*Diagnostic terms defined in Glossary; LRs calculated from data in article; CIs provided by author.


Commentary

A rapid and accurate investigation of the symptom of acute shortness of breath is vital. Clinical and chest radiographic findings have long been used to diagnose HF. Echocardiography is now also used frequently. Recently, BNP levels have been proposed to add diagnostic power in patients with acute dyspnea (1). A series of studies has tested the utility of BNP in the emergency diagnosis of HF (2, 3). The study by Knudsen and colleagues compared the diagnostic value of BNP levels with chest radiographs as adjuncts to clinical findings. Unfortunately, 706 patients were excluded from the original cohort (n = 1586) because they lacked complete information.

Knudsen and colleagues found that both chest radiographic variables and BNP levels provide complementary diagnostic information beyond clinical predictors. The sensitivity of BNP at a low cutpoint (100 pg/mL) compared favorably with chest radiographic findings. This means that BNP levels could be used to rule out HF. However, the specificity of cephalization and interstitial edema was higher than even the highest BNP cutpoint (400 pg/mL). Therefore, some of the classic radiographic findings can better rule in HF.

Hence, BNP levels should not be used instead of chest radiography, because the diagnostic value of both tests is complementary. As pointed out by Knudsen and colleagues, the diagnosis of HF should not be based on a single test. A final study with point-of-care radiographic interpretation and rapid BNP results would be valuable.

Peter Henriksson, MD, PhD
Karolinska Institute at Danderyd University Hospital
Stockholm, Sweden


References

1. Mukoyama M, Nakao K, Hosoda K, et al. Brain natriuretic peptide as a novel cardiac hormone in humans. Evidence for an exquisite dual natriuretic peptide system, atrial natriuretic peptide and brain natriuretic peptide. J Clin Invest. 1991;87:1402-12. [PubMed ID: 1849149]

2. Maisel AS, Krishnaswamy P, Nowak RM, et al. Rapid measurement of B-type natriuretic peptide in the emergency diagnosis of heart failure. N Engl J Med. 2002;347:161-7. [PubMed ID: 12124404]

3. McCullough PA, Nowak RM, McCord J, et al. B-type natriuretic peptide and clinical judgment in emergency diagnosis of heart failure: analysis from Breathing Not Properly (BNP) Multinational Study. Circulation. 2002;106:416-22. [PubMed ID: 12135939]