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Three Part Question

In [patients with Community Acquired Pneumonia] does a [raised NT pro-BNP] confer a [higher mortality]

Clinical Scenario

You review a 67 year old female and diagnose Community Acquired Pneumonia (CAP). A junior colleague had requested NT-proBNP levels as part of the work up, and the value was elevated at 1500pg/ml. The patient has no evidence of heart failure. Based on your previous reading of BNP, you wonder whether this may have prognostic significance.

Search Strategy

Ovid MEDLINE(R) 1948 to June Week 4 2012. EMBASE via the NHS Evidence ‘Health Information Resources’ date of searching 22/06/2012.
Medline:[pneumonia.ti,ab OR exp PNEUMONIA/] AND [‘brain natriuretic peptide*‘.ti,ab OR ‘b-type natriuretic peptide*‘.ti,ab OR exp NATRIURETIC PEPTIDE, BRAIN/OR NT-proBNP.ti,ab] LIMIT to English language.

EMBASE:[pneumonia.ti,ab OR exp PNEUMONIA/] AND [‘brain natriuretic peptide*‘.ti,ab OR ‘b-type natriuretic peptide*‘.ti,ab OR exp NATRIURETIC PEPTIDE, BRAIN/OR NT-proBNP.ti,ab] LIMIT to English Language.

Search Outcome

Two hundred and two papers were identified in total. Three were of sufficient quality and relevance for inclusion

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Jeong et al, 2011, Korea	167 Hospitalised patients with community-acquired pneumonia	Retrospective cohort study	30 day Mortality	NT-proBNP levels were significantly higher in non-survivors compared to survivors (median 841.7 (IQR 267.1-3137.3) pg/ml vs 3658.0 (1863.0-7025.0) pg/ml, p=0.019). NT-proBNP was an independent predictor of mortality (adjusted OR 1.53; 95% CI 1.16 to 2.02, p=0.002)	Different patient population. Non ED and outside of UK. Only hospitalised patients studied. Retrospective study. The reason for BNP testing was not stated. Potential selection bias.
			Comparison of NT-proBNP to existing predictors of mortality	The AUC for NT-proBNP was 0.712 (95% CI, 0.613 to 0.812), which was comparable to those of PSI (0.749, p=0.531) and CURB65 (0.698, p=0.693), but inferior to that of APACHE II (0.831, p=0.037). Adding NT-proBNP to APACHE II, PSI and CURB65 did not significantly increase the AUCs, respectively
Christ-Crain et al, 2008, Switzerland	302 consecutive patients presenting to the emergency department (ED) with CAP	Prospective cohort study	Ability of BNP to predict Mortality (7weeks)	BNP levels were significantly higher in nonsurvivors compared to survivors [median 439.2 (IQR 137.1–1384.6) vs. 114.3 (51.3–359.6) pg mL)1, P < 0.001]	Single centre study
			BNP Mortality prediction compared to PSI	ROC analysis for the prediction of survival the AUC for BNP was comparable to that of PSI (0.75 vs. 0.71, P = 0.52)
			BNP + PSI to predict Mortality	AUC 0.78 vs. 0.71; P = 0.02
			BNP to predict treatment failure	AUC 0.75
Nowak et al, 2012, Switzerland	341 Consecutive patients with suspected CAP presenting to the ED	Prospective cohort study	30 day mortality prediction, comparison of natriuretic peptides, PSI and CURB-65	The AUC was (PSI 0.76, 95% CI 0.71 to 0.81; CURB-65 0.65, 95% CI 0.61 to 0.70; NT-proBNP 0.73, 95% CI 0.67 to 0.77; MR-proANP 0.72, 95% CI 0.67 to 0.77; BNP 0.68, 95% CI 0.63 to 0.73)	Long recruitment period Recruitment interrupted during study Single centre
			Long-term mortality (median follow-up 942 days) prediction, comparison of natriuretic peptides, PSI and CURB-65	The AUC was (PSI 0.72, 95% CI 0.66 to 0.77; NT-proBNP 0.75, 95% CI 0.70 to 0.80; MR-proANP 0.73, 95% CI 0.67 to 0.77, BNP 0.70, 95% CI 0.65 to 0.75)

Comment(s)

The British Thoracic Society favours the CURB-65 score for assessing prognosis in CAP. This is also used to decide on antibiotic treatment and disposition from the emergency department. Although simple, it does have some limitations. It relies on a laboratory value (urea), which can cause delays, and there is interobserver variability in calculating scores. If a bedside blood test such as NT-proBNP could be used for prognostication, this could potentially improve time to treatment and disposition of this patient group. All three studies have shown correlation between BNP or NT-proBNP levels and mortality. NT-proBNP appears to have greater sensitivity and specificity of the two. One study showed that NT-proBNP was comparable to the CURB-65 score. None of the studies was as large as that of Lim et al, which derived the CURB-65 score.

Editor Comment

AUC, area under the curve; CAP, community-acquired pneumonia; ED, emergency department; PSI, pneumonia severity index.

Clinical Bottom Line

B-type natriuretic peptides have prognostic value in CAP. Further prospective studies are needed to assess their application in clinical practice.

References

1. Jeong KY, Kim K, Kim TY, et al. Prognostic value of N-terminal pro-brain natriuretic peptide in hospitalised patients with community-acquired pneumonia Emerg Med J 2011 28: 122-127
2. Christ-Crain T, Breidthardt D, Stolz K, et al Use of B-type natriuretic peptide in the risk stratification of community-acquired pneumonia J Intern Med 2008; 264: 166–176.
3. Nowak A, Breidthardt T, Christ-Crain M, et al. Direct comparison of three natriuretic peptides for prediction of short- and long-term mortality in patients with community-acquired pneumonia. Chest 2012;141:974–82.