Infectious Disease Diagnosis: New Guideline on Lab Tests

Laurie Barclay, MD

July 15, 2013

Microbiological diagnoses based on laboratory testing directly affect patient care and outcomes, including hospital infection control, duration of hospitalization, and laboratory efficiency, according to new guidelines from the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology.

The new recommendations, which address appropriate and accurate use of laboratory tests to diagnose infectious diseases (IDs), were published online July 10 in Clinical Infectious Diseases by Ellen Jo Baron, PhD, from the Department of Pathology, Stanford University School of Medicine, and Cepheid, R&D, Sunnyvale, California, and colleagues.

Because laboratory testing underlies approximately 60% to 70% of diagnoses and treatment decisions, inappropriate or poorly performed tests may result in wrong diagnoses, unnecessary treatment, and higher costs. The guideline aims to educate physicians and laboratory technicians about use of specific tests in various settings, identification of tests adding little or no value, and proper techniques of specimen collection and handling. It is not intended to replace clinical judgment but, rather, to support individualized decision-making.

Organized for Easy Use

This guideline is a departure from the usual approach, according to IDSA board member Paul G. Auwaerter, MD, MBA, clinical director and professor of medicine, Division of Infectious Diseases and Division of General Internal Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland.

"This will be a living document regularly updated so that clinicians have a concise reference to best testing strategy for IDs," Dr. Auwaerter told Medscape Medical News. "In the past, a clinician would have to look into many different references; for example, to understand how to test for pulmonary infection with the differential diagnosis including tuberculosis, histoplasmosis, [and] cryptococcosis, would likely require the individual to look at 3 different pathogen sections. Now all diagnostic recommendations are under one roof."

The guidelines include recommendations for specific anatomic sites and systems, including blood, cardiovascular, central nervous system, ocular, head and neck soft tissue, upper and lower respiratory, gastrointestinal, intraabdominal, bone and joints, skin and soft tissue, and urogenital systems. Furthermore, the guidelines address what tests to request when specific pathogens are suspected, including tickborne rickettsial infections, viruses, and parasitic infections.

"My belief is that if information can be easily navigated, then clinicians will be more apt to look up information," Dr. Auwaerter added. "These guidelines should offer an excellent approach for quickly looking up information as test ordering is needed...in a busy office or hospital setting."

Each of the system and pathogen sections specifies the most reliable tests to order, specimen management techniques, and issues regarding test methods, including specialized laboratory requirement or prolonged turnaround time.

Those involved in specimen management, including nurses, physicians, and laboratory staff, should use appropriate collection devices, obtain sufficient specimen volume, maintain proper specimen temperature, and transport the specimen within an ideal time frame.

Clinical Implications

"The diagnostic microbiology/virology laboratory is as critically important to the ID physician as an high-quality X-ray is to the radiologist," Lucy S. Tompkins, MD, PhD, professor of medicine, microbiology and immunology at Stanford University School of Medicine, told Medscape Medical News. "The quality of the laboratory services must be excellent in order for the ID physician and other physicians to have confidence that the results will lead to an accurate diagnosis or treatment," continued Dr. Tompkins, who was not involved in the work.

"The likely implications for patients if these guidelines were adopted would certainly be to improve outcomes through rapid, accurate diagnostic techniques, standardized susceptibility testing of antimicrobials, and as a critically important partner to the infection prevention department and the antibiotic utilization program," said Dr. Tompkins, who is also Hospital Epidemiologist and Medical Director, Infection Prevention and Control Department of Stanford Hospital and clinics. "Local, state, and governmental public health are also dependent upon laboratories for surveillance and to identify trends in emerging IDs."

"I would urge all physicians to 'know your laboratory' and to select one that adopts validated protocols, provides accurate and helpful interpretations of results, provides reasonably rapid turnaround times, and is certified by appropriate agencies," Dr. Tompkins said. "It is also important to know where the laboratory may send tests that are not performed in-house. A high-quality laboratory should have an experienced and well-trained director who has expertise in diagnostic testing as well as in clinical IDs.

Specific Principles of Specimen Management

  • To avoid compromising test results, specimens of poor quality must be rejected. Microbiologists should call physicians to clarify and resolve problems with specimen submissions.

  • Physicians should not request a report of "everything that grows," as irrelevant information could lead to inaccurate diagnosis and inappropriate therapy.

  • Careful collection is essential to avoid specimen contamination from normal microbiota, especially for specimens from the lower respiratory tract, nasal sinuses, superficial wounds, fistulae, and similar sites.

  • A specimen swab may contain insufficient material to ensure accurate diagnosis and is easily contaminated. An entire tissue, aspirate, or fluid specimen is needed. Flocked swabs are more efficient than polyethylene terephthalate, rayon, and cotton.

  • Legal challenges could arise if the laboratory does not follow its procedure manual.

  • Specimens should be collected before starting antibiotics to avoid compromising culture results.

  • Susceptibility testing should be limited to clinically significant isolates.

  • Laboratory test results should be accurate, significant, and clinically relevant.

  • Although technical policy is the responsibility of the laboratory, not the medical staff, good communication and mutual respect foster collaborative policies.

  • Complete and accurate specimen labelling is required (eg, dog bite wound, right forefinger).

Several of the guidelines authors reported various financial disclosures with manufacturers of diagnostic testing. Full conflict-of-interest information is available on the journal's Web site. Dr. Tompkins and Dr. Auwaerter have disclosed no relevant financial relationships.

Clin Infect Dis. Published online July 10, 2013. Full text

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