Performance of 45 laboratories participating in a proficiency testing program for Lyme disease serology.

OBJECTIVE--We show that significant interlaboratory and intralaboratory variations exist in Lyme disease proficiency testing. DESIGN--Six case-defined Lyme serum samples and three serum samples from individuals with no history of Lyme disease were randomized in four shipments and distributed to 45 participating laboratories. RESULTS--Interlaboratory and intralaboratory performances were highly variable. Approximately 4% to 21% of laboratories failed to identify correctly positive serum samples with titers of 512 or more using polyvalent serum or immunoglobulin G conjugates. With lower levels of anti-Borrelia burgdorferi antibody in the serum sample, approximately 55% of participating laboratories did not identify a case-defined serum. There was also a striking inability of many laboratories to reproduce their results on split samples from the same individual. In addition, 2% to 7% of laboratories identified serum samples from individuals with no known exposure to B burgdorferi as positive using polyvalent serum. The false positivity rate increased to 27% with the use of immunoglobulin G conjugate. CONCLUSIONS--Our results indicate that there is an urgent need for standardization of current testing methodologies. Until a national commitment is made, serological testing for Lyme disease will be of questionable value for the diagnosis of the disease.     

Performance of the microscopic observation drug susceptibility assay in pyrazinamide susceptibility testing for Mycobacterium tuberculosis

Background Drug susceptibility assay is very important in tuberculosis therapy. Pyrazinamide is a first line antituberculosis drug and diagnosis of its resistance in Mycobacterium tuberculosis （M. tuberculosis） is difficult and time consuming by conventional methods. In this study, we aimed to evaluate the performance of the microscopic observation drug susceptibility （MODS） assay in the detection of pyrazinamide resistance in M. tuberculosis relative to the conventional Wayne assay and Lowenstein-Jensen （L J） proportion method. Methods M. tuberculosis clinical isolates （n=132） were tested by the MODS and the Wayne assay： the results were compared with those obtained by the LJ proportion method. Mutations in the gene were identified by direct sequencing of the pncA genes of all isolates in which pyrazinamide resistance was detected by any of the three methods. Results Compared to the LJ results, the sensitivity and specificity of the MODS assay were 97.8% and 96.5% respectively; the sensitivity and specificity of the Wayne assay were 87.0% and 97.7% respectively. Mutations in the pncA gene were found in 41 of 46 strains that were pyrazinamide resistant （3 tests）, in 1 of the 4 strains （LJ only）, in 42 of 48 strains （at least I test）, but no mutations in 1 strain sensitive according to the MODS assay only. The MODS assay, Wayne assay and LJ proportion method provided results in a median time of 6, 7 and 26 days respectively. Conclusions MODS assay offers a rapid, simple and reliable method for the detection of pyrazinamide resistance in M. tuberculosis and is an optimal alternative method in resource limited countries.     

Clinical issues in cholesterol testing

Lipid investigators have begun to examine the biological sources of variation in serum cholesterol levels and to seek ways to accurately measure the total cholesterol (TC) level in the serum of a patient. A person's TC level varies primarily because of the effects from seasonal changes, behavioral changes, and illness. Results of studies of the effect of seasonal changes indicate that serum TC and obesity increase during winter and decrease during summer. Behavioral sources of variation include diet, alcohol intake, smoking, and exercise. Clinical sources of TC level variation include all illnesses. The physician can help control sources of variation by recognizing their causes, by advising of the effect that behavioral risk factors have on cholesterol levels, and by using the average of results for multiple specimens to estimate the true value of serum cholesterol in a patient.     

Noninvasive cardiac testing in women

Coronary artery disease (CAD) is a leading cause of morbidity and mortality among men and women. Although substantial research efforts have refined diagnosis and treatment strategies for patients at risk, the detection of CAD in women can be problematic. Atypical chest pain is not only more common among women than men, but the predictive value of traditional risk factors is also different for women and men. Moreover, sex-specific issues in the selection of an appropriate noninvasive diagnostic test must be considered. This article reviews the challenges inherent in the evaluation of chest pain in women as well as the strengths and limitations of the diagnostic stress-testing modalities commonly used.