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Three Part Question

In [patients presenting as an emergency with acute shortness of breath] do [C Reactive Protein levels] help in [differentiating between the diagnoses of chest infection or heart failure]?

Clinical Scenario

A 70 year old man presents to the emergency department with acute shortness of breath. You wonder whether sending a sample of his blood for C Reactive Protein levels will help differentiate between the diagnoses of pneumonia or heart failure.

Search Strategy

Medline using the OVID interface 1966 to September week 4 2008:
{[c reactive protein.mp. or exp C-Reactive Protein or CRP]} AND {[exp respiratory tract infections OR exp respiratory tract diseases OR exp pneumonia OR pneumonia.mp]} OR {[exp dyspnea OR dyspnoea.mp]} OR {[ exp heart failure, congestive OR exp ventricular dysfunction, right OR exp ventricular dysfunction, left OR heart failure.mp OR exp heart failure/]} LIMIT TO {(humans and English language and ("diagnosis (sensitivity)" "all adult (19 plus years)" and abstracts

Search Outcome

601 papers found of which 3 were found to be relevant one of which was a systematic review that contained data from other relevant papers

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Gottdiener et al 2000 USA	5,888 elderly people (>65 yrs)	Prospective population based study	Development of CHF	CRP >7mg/litre has a relative risk of 1.93	Not really what we are looking at. Study population specific to elderly.
Rutten et al 2005 Netherlands	1186 patients aged > or =65 with COPD who did not have diagnosis of HF confirmed by cardiologist	Cross sectional diagnostic study	Diagnosis of Heart Failure	CRP has limited added value to clinical examination and routine bloods	Setting is Primary care. Patient group studied very specific.
Van der Meer et al 2005 Netherlands	6 papers using infiltrate on chest x-ray as a reference test	Systematic Review	Clinical utility of CRP in the detection of radiologically proven pneumonia	Sensitivities ranged from 10 to 98% and specificities ranged from 44 to 99%	None of studies included met review validity criteria
			Relation of CRP with infiltrate	AUC = 0.80

Comment(s)

Acute shortness of breath is a common presentation to the Emergency Department and it has a long list of differential diagnoses. Two of the common diagnoses are pneumonia and heart failure. If a simple blood test for CRP levels could differentiate between the two this would aid clinical practice both for doctors in the ED and acute physicians. Following a search of the evidence no papers were found which looked at this relationship directly therefore, the search was widened and evidence taken from studies examining different inclusion criteria and different outcomes to the one we specifically wanted. This evidence was examined to see if it could be extrapolate to provide the best answer to our question. There were many more papers found on the use of CRP in the diagnosis of pneumonia than there were for that of heart failure (although the role of CRP in myocardial infarction is being extensively studied). The best level of evidence found for the use of CRP in the diagnosis of pneumonia was from a Systematic Review which found that the area under the ROC was 0.80 which shows that it is neither a particularly good or bad test. The best evidence found for the use of CRP in the diagnosis of heart failure was a cross sectional diagnostic study which found that CRP had limited diagnostic value. Unfortunately this study was done in primary care and it is difficult to extrapolate these findings to the ED. Our findings do not allow us to give a definitive answer to our 3 part question.

Clinical Bottom Line

There is no evidence for the use of CRP to discriminate between a diagnosis of pneumonia and heart failure in patients who have acute shortness of breath.

References

1. Gottdiener, J.S., A.M. Arnold, G.P. Aurigemma, J.F. Polak, R.P. Tracy & D.W. Kitzman, et al Predictors of congestive heart failure in the elderly: the Cardiovascular Health Study Journal of the American College of Cardiology 2000; 35, 1628-1637.
2. Rutten, F.H., K.G. Moons, M.J. Cramer, D.E. Grobbee, N.P. Zuithoff & J.W. Lammers, et al Recognising heart failure in elderly patients with stable chronic obstructive pulmonary disease in primary care: cross sectional diagnostic study BMJ 2005; 331, 1379
3. van der Meer, V., A.K. Neven, P.J. van den Broek & W.J. Assendelft Diagnostic value of C reactive protein in infections of the lower respiratory tract: systematic review BMJ 2005; 331, 26.