Evidence-based medicine is the approach used by doctors to make rational clinical decisions based on rigorous, well-controlled studies. By minimizing hunches, gut feelings, and anecdotal evidence, physicians and patients can follow recommendations that are most likely to have a positive outcome. Practice of evidence-based medicine has improved patient quality of life, prevented unnecessary procedures, and improved patient recovery times.
Evidence-based medicine isn’t limited to patient therapy, however – it plays a strong role in diagnostics as well. Clinical microbiologists are using this approach to determine best-practices for sample collection and storage, two factors that can greatly impact the microbiological contents of a specimen. A recently published review in Clinical Microbiology Reviews investigated data supporting recommendations for urine collection and storage prior to processing. This is in an effort to standardize these practices among clinics for consistent and reproducible results.
Urine samples are some of the most frequently collected clinical specimens. Urinary tract infections (UTIs) are the most common bacterial infections the United States, accounting for 8.1 million physician visits annually, and urinanalysis is an important part of proper diagnosis. They are often caused by gram-negative bacteria, but ensuring culture of the causative microbe, and not a contaminant, is necessary to identify the correct etiology.
A number of guidelines exist regarding specimen collection, including those regarding washing before collection and clean catch of mid-stream urine. After collection, samples are either refrigerated or preserved with boric acid for up to 24 hours before processing. The panel of experts involved in the study delved into the literature to see how strongly the data supported these recommendations. This work was sponsored by the American Society for Microbiology in collaboration with the Center for Disease Control and Prevention's Division of Laboratory Programs, Standards, and Services through a Laboratory Medicine Best Practices Program Memorandum of Understanding.
The researchers focused on eight specific clinical questions (see inset, right). Beginning with over 5000 studies, they strategically concentrated the relevant articles to 171 using applicable search terminology. Exclusion of poor-quality data further winnowed the relevant articles down to a final 35 that met all criteria: 10 studies on storage and 25 on collection (14 studies on collection from children/infants, 8 studies with women subjects, and only 3 studies with men).
All the studies on specimen storage supported the use of either refrigeration or boric acid addition for sample preservation. The review panel further concluded that samples stored at room temperature for over four hours should be discarded, since overgrowth quickly occurs in this condition.
Sample collection literature was not as coinciding. While midstream clean-catch was associated strongly with reduced contamination in adults, the overall effect of perineal cleansing was uncertain for women. However, the overall strength of the body of evidence around these conclusions was low. Although there were slightly more studies involving children and infants, the results still varied. In this patient population, cleansing did reduce contamination for midstream collection. Diaper or sterile urine bag collection is often used for very young (read: not potty-trained) children, but these methods were not recommended by the panel.
The most important finding of this study may be the lack of rigorous studies examining urine collection and storage. Most studies were observational and poorly controlled; some failed to report data for all study participants. These are investigational aspects that can be more systematically addressed in future research. Better pre-processing specimen handling will decrease sample contamination events, increase the speed and accuracy of diagnoses, and lead to more consistent results. In the end, both patient and health-care provider benefit from more timely treatment and more efficient (and thus less expensive) health care costs.
These meta-analyses serve an additional purpose. Clinicians have many tasks pulling at their attention – reading and synthesizing all the relevant studies is something for which many simply don’t have time. Recommendations by those willing to dig deep into the literature provide a valuable resource for the entire field. The discovered gap in knowledge can guide future studies to develop these type of recommendations. To this end, the study included suggested questions and recommendations to help improve forthcoming project design and analysis.
-- Julie Wolf