Is that test necessary?: blood cultures in pneumonia

In response to a question in the American Society of Microbiology laboratory discussion group (DivC), I sent this message:

In fact, as Dr. Manasse suspects, blood cultures are the subject of the Joint Commission Core Measure PN-3b.

However, careful examination of the measure does not justify the use of blood culture tests in all Emergency Department patients with pneumonia.

Core Measure PN-3b "Blood Cultures Performed in the Emergency Department Prior to Initial Antibiotic Received in Hospital" is described at:
http://manual.jointcommission.org/bin/view/Manual/MIF0006

As you can see there, the measure is justified by "Published pneumonia treatment guidelines recommend performance of blood cultures for all inpatients to optimize therapy" and lists several published guidelines. The most recent citation is:

Mandell LA, Wunderink RG, Anzueto A, et al. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin. Infect. Dis. 2007;44 Suppl 2:S27-72
(http://www.guideline.gov/summary/summary.aspx?ss=15&doc_id=10560)

Mandell et al. write that "Recommendations for diagnostic testing remain controversial. The overall low yield and infrequent positive impact on clinical care argue against the routine use of common tests, such as blood and sputum cultures", however they add that "cultures may have a major impact on the care of an individual patient" and identify the individual patients for whom "pretreatment blood samples for culture...should be obtained" as those with:

• Intensive care unit admission
• Cavitary infiltrates
• Leukopenia
• Active alcohol abuse
• Chronic severe liver disease
• Asplenia (anatomic or functional)
• Positive pneumococcal Urinary Antigen Test result
• Pleural effusion

(Table 5 and Recommendation # 12)

Severe pneumonia that justifies blood culture testing, in addition to the criteria above, also includes patients with three or more of the following "minor" criteria:

• Respiratory rate >=30 breaths/min
• PaO2/FiO2 ratio =<250 li="">
• Multilobar infiltrates
• Confusion/disorientation
• Uremia (BUN level, >=20 mg/dL)
• Hypothermia (core temperature, <36>
• Thrombocytopenia (platelet count, <100>
• Hypotension requiring aggressive fluid resuscitation
• Hypoglycemia (in nondiabetic patients)
• Hyponatremia
• Unexplained metabolic acidosis or elevated lactate level

For the rest of patients with less severe pneumonia, recommendation #11 applies: "Routine diagnostic tests to identify an etiologic diagnosis are optional for outpatients with Community Acquired Pneumonia".

Thus, Denise Jones' Emergency Department (ED) physicians are only 33.3% correct in requesting blood cultures in patients with low oxygen saturation, since hypoxia should be accompanied by two other minor criteria to justify the test, according to the authorities cited by the Joint Commission.

The criteria listed above require a basic patient assessment that can be completed quickly in the ED (problem-oriented patient history, measurement of blood pressure, temperature and respiration rate, chest x-ray, CBC, urine antigen tests and serum metabolic profile plus alcohol and lactic acid levels) so that they will only slightly delay administration of antibiotics.

For these reasons, and armed with the information above, the laboratory could argue convincingly against the need to obtain a sample before deciding whether a blood culture will be needed.

In addition to the unnecessary work imposed on usually overwhelmed ED and laboratory staffs, the invasive nature of the procedure and the cost of supplies and equipment, there is the problem of false negatives: in samples kept at room temperature, some organisms might grow to exceed the CO2 detection threshold so that their presence will not be detected by the continuous CO2 monitoring system when they are eventually placed in the blood culture incubator. BioMérieux sent a BacT/Alert system notification to that effect a couple of years ago.

False positive results could also be more frequent under these circumstances. I have noticed that often, blood culture contamination rates are higher in the ED than in in-patient services (is that also your experience?) and I wonder whether sterility precautions are observed as scrupulously when the person drawing the sample is not sure that it will, in fact, be used.

We are all compelled to avoid waste and error in health care, especially now that the prospect of real reform is on the horizon. Laboratory efforts to fine-tune accreditation demands so that they make sense, are a valuable contribution. Denise: go ahead and fight that battle using the information above.