Integrative Management of Respiratory Illnesses, continued…
Laboratory Testing and Imaging
Initial laboratory testing in suspected CAP is not specific for diagnosis, but is important in predicting mortality and the appropriate context for care. Based on history, risk factors, and potential exposures, a more intensive work-up for the underlying microbial etiology of CAP may be in order. The most indicative laboratory test for the presence of CAP is a white blood cell count (WBC), which will typically demonstrate leukocytosis which may be markedly elevated at 15,000 to 30,000 cells per cubic millimeter and will typically demonstrate a left shift. A WBC value over 10,400/mm3 has a positive likelihood ratio of 3.4 for presence of CAP. Leukopenia may be present instead and is generally an indicator of poor prognosis.12,14
The blood urea nitrogen level (BUN) should be drawn, as it is useful in determining whether the patient is a candidate for outpatient treatment. The blood platelet count is also a useful measure in predicting severe CAP.7 Hypoglycemia, specifically a blood glucose level less than 70 mg/dL at presentation, is an indicator of increased 30-day mortality.18 More recent investigations have considered the value of serum cortisol testing as an independent predictor of CAP severity, prognosis, and mortality.19
The high success rate of empirical therapy for outpatient treatment of CAP (> 95% in some studies), renders routine laboratory testing for infectious etiology optional in the majority of cases of outpatient appropriate CAP.1,12,20 However, it is important to investigate for and recognize when the underlying infectious agent may be of significance to public health or suggestive of a “critical microbe.” There are four tests that should be considered based on the history, risk factors, and clinical findings in any case suspected for CAP: pneumoccocal urinary antigen test, Legionella urinary antigen test, sputum cultures, and blood cultures. A full discussion of testing for microbial etiology in the outpatient setting is available in the Infectious Disease Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults (Mandell et al.) and goes beyond what is discussed here.21
It is recommended that any patient suspected for CAP with a history of any travel over the previous two-week period be tested for Legionella infection by urinary antigen testing. Patients who abuse alcohol, show evidence of pleural effusion on chest radiography, or do not respond to outpatient therapy should also be tested for urinary Legionella antigen.
The urinary pneumococcal antigen should be tested in patients who suffer from alcohol abuse or who have chronic severe liver disease of any etiology. Asplenia and leukopenia are also conditions that should prompt this test. As above, when outpatient treatment fails or when there is radiographic evidence of pleural effusion, the urinary pneumococcal antigen test should be completed.
Sputum and blood cultures should be completed in those with a positive pneumococcal antigen test as well as in those with pleural effusion, alcohol abuse, or evidence of cavitary infiltrates on chest radiography. Sputum cultures are also indicated in those with severe obstructive lung disease, those with a positive urinary Legionella antigen test, and those who fail outpatient treatment. Blood cultures are also indicated in those who are asplenic, leukopenic, have severe chronic liver disease, or have a positive urinary pneumoccocal antigen test.21
Routine PA and lateral chest radiograph (CXR) should be performed in the setting of acute respiratory illness if any one of the following is present: core body temperature greater than 100 ºF, pulse greater than 100 beats/minute, or respiratory rate over 20 breaths/minute. It should also be performed if any two of the following are present: decreased breath sounds, crackles/rales, absence of asthma.12,22
When to Hospitalize
The first step in clinical decision-making and patient management in any case of suspected CAP is to decide upon the need for hospitalization.1 A large number of CAP cases will be amenable to outpatient treatment. Moreover, hospitalization of the CAP patient increases risks of certain complications, especially nosocomial infections, superinfections, and thromboembolic events.1 The estimated cost of a single hospitalization for CAP ranges from $3000 to $13,000.23 However, in CAP cases where it is necessary, timely hospitalization can be life-saving. Several predictions rules have been created and validated over recent years to help clinicians safely determine and document the appropriateness of outpatient management or hospital referral of CAP. The most rigorously validated of these measures is the Pneumonia Severity Index (PSI). Despite much redeeming value, the PSI is cumbersome for use in the primary care setting and is hampered by its inability to always recognize the most severe cases of illness.24 The British Thoracic Society has developed the CURB 65 and CRB 65 prediction rules, which are practical in all settings.
The CURB 65 prediction rule uses the parameters of confusion, uremia (BUN >20 mg/dL), respiratory rate (> 30/min), blood pressure (< 90/60), and age (65 years or more) to predict the likelihood of mortality, and therefore the appropriate care setting, for cases of CAP. Each of the five variables in the CURB 65 score is afforded 1 point. A score of 0 to 1 point confers a 30-day mortality risk of less than 2.1% and determines a safe circumstance for treating the patient in the outpatient setting. A score of 2 points confers a 30-day mortality risk over 9% and demands inpatient treatment; patients with scores of 3 or more points should be treated in intensive care as their mortality ranges from 15% to 40%.7
A validated, clinically useful modification of the CURB 65 score is the CRB 65 score. CRB 65 omits the measurement of serum BUN levels, which may not be immediately available in all clinical settings. The score is based on confusion, respiratory rate, blood pressure, and age, only. As a result, only patients with a CRB 65 score of 0 are deemed appropriate for outpatient management. Several other factors also need to be considered when determining the relative safety of treating CAP in the outpatient setting.25
The evaluation of comorbidities and social circumstances of each patient suspected for CAP is instrumental when deciding upon the appropriateness of outpatient management. The functional status and living situation of the patient must be considered, as must her/his ability to comply with treatment and maintain oral intake. The history of substance use should also be considered. Comorbidities that predispose patients to complications or more severe illness should also be taken under consideration and include COPD, diabetes, immunosuppressive therapies and conditions, liver or kidney disease, asplenism, and alcoholism.26
