When should a chest x-ray be used to evaluate acute-onset productive cough for adults?

,

Clinical Inquiries

When should a chest x-ray be used to evaluate acute-onset productive cough for adults?

J Fam Pract. 2005 December;54(12):1081-1083

By

Paul Pisarik, MD, MPH

PDF Download

References

1. Diehr P, Wood RW, Bushyhead J, Krueger L, Wolcott B, Tompkins RK. Prediction of pneumonia in outpatients with acute cough-a statistical approach. J Chronic Dis 1984;37:215-225.

2. Emerman CL, Dawson N, Speroff T, Siciliano C, Effron D, Rashad F, et al. Comparison of physician judgment and decision aids for ordering chest radiographs for pneumonia in outpatients. Ann Emerg Med 1991;20:1215-1219.

3. Cypress BK. Patients’ reasons for visiting physicians: National Ambulatory Medical Care Survey: United States, 1977-1978. Vital Health Stat 13 1981;56:1-134.

4. Heckerling PS, Tape TG, Wigton RS, et al. Clinical prediction rule for pulmonary infiltrates. Ann Intern Med 1990;113:664-670.

5. Gennis P, Gallagher J, Falvo C, Baker S, Than W. Clinical criteria for the detection of pneumonia in adults: guidelines for ordering chest roentgenograms in the emergency department. J Emerg Med 1989;7:263-268.

6. Singal BM, Hedges JR, Radack KL. Decision rules and clinical prediction of pneumonia: evaluation of lowyield criteria. Ann Emerg Med 1989;18:13-20.

7. Bushyhead JB, Wood RW, Tompkins RK, Wolcott BW, Diehr P. The effect of chest radiographs on the management and clinical course of patients with acute cough. Med Care 1983;1:661-673.

8. Macfarlane J, Holmes W, Gard P, et al. Prospective study of the incidence, aetiology and outcome of adult lower respiratory tract illness in the community. Thorax 2001;56:109-114.

9. Bartlett JG, Dowell SF, Mandell LA, File TM, Jr, Musher DM, Fine MJ. Practice guidelines for the management of community-acquired pneumonia in adults. Clin Infect Dis 2000;31:347-382.

10. Niederman MS, Mandell LA, Anzueto A, et al. Guidelines for the management of adults with community-acquired pneumonia.Diagnosis, assessment of severity, antimicrobial therapy, and prevention. Am J Respir Crit Care Med 2001;163:1730-1754.

11. Mandel LJ, Marrie TJ, Grossman RF, Chow AW, Hyland RH. Canadian guidelines for the initial management of community-acquired pneumonia: an evidence-based update by the Canadian Infectious Diseases Society and the Canadian Thoracic Society. The Canadian Community-Acquired Pneumonia Working Group. Clin Infect Dis 2000;31:383-421.

12. Heffelfinger JD, Dowell SF, Jorgensen JH, et al. Management of community-acquired pneumonia in the era of pneumococcal resistance: a report from the drug-resistant streptococcus pneumoniae therapeutic working group. Arch Intern Med 2000;160:1399-1408.

13. British Thoracic Society Standards of Care Committee BTS guidelines for the management of communityacquired pneumonia in adults. Thorax 2001;56:IV1-164.

14. European Respiratory Society Task Force Report. Guidelines for management of adult communityacquired lower respiratory tract infections. Eur Respir J 1998;11:986-991.

EVIDENCE-BASED ANSWER

Even though the most common reason to order a chest x-ray in the evaluation of an acute-onset, productive cough is to rule out pneumonia, there is no strong evidence to help a physician decide when to order this chest x-ray. However, acute cough patients who have rhinorrhea, sore throat, respiratory rate ≤25 breaths per minute, temperature <100°F, and the absence of night sweats, myalgia, and all-day sputum production, have minimal to no risk of pneumonia and thus do not need a chest x-ray (strength of recommendation: A, based on a clinical decision rule validated in 2 high-quality cohort studies).^1,2

CLINICAL COMMENTARY

Decision rule not perfect, but still better than physician’s own judgment

Drew E. Malloy, MD
University of Arizona, Campus Health Services, Tucson

This decision rule for when to order a chest x-ray was validated in a study of 1758 adult, nonpregnant, ambulatory patients with acute productive cough of less than 4 weeks. Using a threshold score of ≥1 point detected 25 of 46 pneumonias (59%), compared with a detection rate of 33% without the detection rule. All that great stuff we learned in our training about the history and physical exam missed a whopping 67% of pneumonias. The application of the decision rule still missed 41% (21 of 46 pneumonias), but that is a lot better than usual physician judgment. Surprisingly, the patients in whom pneumonias were missed did not reconsult more frequently, and we are left to believe they all did well. This interesting tidbit begs the question of whether chest x-ray or treatment is required for anyone not sick enough to be in the hospital with an acute respiratory infection. Will using this decision rule in your practice reduce unnecessary x-ray or antibiotics? Maybe. I have already tried this decision rule in my practice and have found no surprises so far.

Evidence summary

Even though the chest x-ray is as close to a gold standard as we have for diagnosing pneumonia (FIGURE), in practice it is only ordered about 11% of the time.³ Individual clinical findings such as pulse above 100 beats per minute, respiratory rate above 25 breaths per minute, temperature above 99.9°F, local dullness to percussion, rales, asymmetric respirations, pleural rubs, egophony, increased fremitus, and cachexia are weak predictors of pneumonia, being present in 4% to 28% of radiographically proven pneumonia.¹ Individual symptoms such as chills, night sweats, fever, and sputum production are found in 31% to 79% of those with pneumonia, but also in 18% to 62% of those without pneumonia. Therefore prediction rules, using combinations of statistically significant factors, have been developed to help us decide when to order a chest x-ray to diagnose pneumonia.

Unfortunately, almost all studies that have developed prediction rules preselected higher-risk patients—those who had already been selected to get a chest x-ray (based on unknown signs and symptoms).^4-6 The signs and symptoms that predict pneumonia for patients already selected for a chest x-ray may be different than for unselected patients. These studies also assume that physician judgment in ordering a chest x-ray is 100% sensitive and thus that all patients with pneumonia have been correctly identified.

Fast Track

Patients with infection changes on x-ray did not reconsult more than those without, implying at least some outpatient pneumonias are self-limiting

Only 2 studies have done chest x-rays on all nonpregnant adults with a first visit for a cough of less than 4 weeks duration and no other exclusion criteria.^1,7 Physicians indicated that they would have wanted to order chest x-rays in 12% to 15% of those patients (similar to national statistics), but they would have detected only one third of all the pneumonias. One of these studies looked at signs and symptoms and did a stepwise discriminant analysis with those factors that were significant for pneumonia and then assigned point values to them (TABLE 1 AND 2).¹ By limiting chest x-rays to those patients with a clinical score of 1 or greater, 13% of patients would have a chest x-ray with 59% of pneumonias detected—almost twice as many as detected without the prediction rule.

One problem with the application of prediction rules is that they are always associated with missed pneumonias. Not much is known about the pneumonias that would be missed by applying the prediction rule or, for that matter, those that are missed using physician judgment. In the above study, before seeing the results of the x-rays, only 50% of the pneumonia patients would have been prescribed antibiotics. In another study where patients with lower respiratory tract infection all received radiographs but the treating physicians did not see the x-ray results, only half of the patients with radiographic changes consistent with pneumonia were given antibiotics.⁸ Surprisingly, those patients with infection changes on chest x-ray were no more likely to reconsult than those without those changes, implying that a certain percentage of outpatient pneumonias are self-limiting.⁷