Molecular biology made easy. The polymerase chain reaction

Advanced diagnostic methods in oral and maxillofacial pathology. Part I: molecular methods

The practice of pathology is currently undergoing significant change, in large part due to advances in the analysis of DNA, RNA, and proteins in tissues. These advances have permitted improved biologic insights into many developmental, inflammatory, metabolic, infectious, and neoplastic diseases. Moreover, molecular analysis has also led to improvements in accuracy of disease diagnosis and classification. It is likely that, in the future, these methods will increasingly enter into the day-to-day diagnosis and management of patients. The pathologist will continue to play a fundamental role in diagnosis and will likely be in a pivotal position to guide the implementation and interpretation of these tests as they move from the research laboratory into diagnostic pathology. The purpose of this 2-part series is to provide an overview of the principles and applications of current molecular biologic and immunologic tests. Part I will discuss the biologic fundamentals of DNA, RNA, and proteins and the methods that are currently available or likely to become available to the pathologist in the next several years for their isolation and analysis in tissue biopsies.

The role of intraoperative gram stain in the diagnosis of infection during revision total hip arthroplasty

A total of 202 revision hip arthroplasties in 178 patients, over a 2-year period, were evaluated prospectively. Intraoperative Gram stains were obtained from periprosthetic tissues in all cases. Of these, a definitive diagnosis of infection, using defined criteria, was established in 35 cases. Of these 35 patients, 17 had received antibiotics before surgery. The intraoperative cultures were positive in 8 of the 17 patients who had received antibiotics and 17 of the 18 patients who had not received preoperative antibiotics. In 1 infected case, intraoperative cultures of periprosthetic tissues failed to reveal bacterial growth, despite the fact that the patient received no preoperative antibiotics. Overall, there were 5 true-positive Gram stain results, 172 true-negative results, 3 false-positive results, and 22 false-negative results. The sensitivity of the Gram stain was 19%, specificity was 98%, predictive value of a positive test was 63%, and predictive value of a negative test was 89%. These results suggest that the intraoperative Gram stain is not a sensitive tool for the diagnosis of infection and should not be used when attempting to diagnose infection intraoperatively.

False-positive polymerase chain reaction results for human papillomavirus in lichen planus. Potential laboratory pitfalls of this procedure

BACKGROUND

The polymerase chain reaction (PCR) is a common tool in laboratory evaluation of tissue samples. It has been particularly useful in testing for nucleic acids of infectious organisms implicated in the pathogenesis of cutaneous diseases.

OBJECTIVE

Our purpose was to evaluate archival biopsy material (paraffin-embedded) of lichen planus for human papillomavirus (HPV) DNA with PCR and in situ hybridization (ISH).

METHODS

Tissue sections were obtained from 13 specimens of lichen planus and 10 control tissues. Standard methods for PCR and ISH were used to evaluate the presence of HPV DNA. RESULTS. Initial PCR results demonstrated HPV DNA in 11 of 13 specimens and in none of the control tissue. However, testing for specific HPV types revealed nucleic acid contamination. ISH was negative in all specimens.

CONCLUSION

Accurate evaluation of tissue with PCR is difficult because of the procedure's profound sensitivity. Positive results reported in the literature should be viewed with caution. Potential causes for false-positive and false-negative results should be considered.