Update on the role of pathology and laboratory medicine in diagnosing periprosthetic infection.

Technological and implant design advances have helped reduce the frequency of aseptic total joint arthroplasty failure, but periprosthetic joint infections (PJI) remain a clinical important problem with high patient morbidity. Misinterpreting PJI as aseptic mechanical loosening commonly leads to unsatisfactory revision arthroplasty, persistent infection, and poor long-term results. While there is no single "gold standard" diagnostic test for PJI, recent collaborative efforts by Orthopaedic and Infectious Disease Societies have developed algorithms for diagnosing PJI. However, the efficacy of individual tests as well as diagnostic thresholds are controversial. We review the recommended thresholds for commonly used screening tests as well as tissue histopathology and confirmatory tests to diagnose periprosthetic infection. We also update lesser-known laboratory tests, and we briefly summarize rapidly evolving molecular tests to diagnose periprosthetic infection. Pathologists hold a critical role in assisting with PJI diagnosis, maintaining laboratory test quality and interpreting test results. Collaboration between clinicians and pathologists is essential to provide optimal patient care and reduce the burden of PJI.

Highly sensitive detection of Staphylococcus aureus directly from patient blood.

BACKGROUND: Rapid detection of bloodstream infections (BSIs) can be lifesaving. We investigated the sample processing and assay parameters necessary for highly-sensitive detection of bloodstream bacteria, using Staphylococcus aureus as a model pathogen and an automated fluidic sample processing-polymerase chain reaction (PCR) platform as a model diagnostic system. METHODOLOGY/PRINCIPAL FINDINGS: We compared a short 128 bp amplicon hemi-nested PCR and a relatively shorter 79 bp amplicon nested PCR targeting the S. aureus nuc and sodA genes, respectively. The sodA nested assay showed an enhanced limit of detection (LOD) of 5 genomic copies per reaction or 10 colony forming units (CFU) per ml blood over 50 copies per reaction or 50 CFU/ml for the nuc assay. To establish optimal extraction protocols, we investigated the relative abundance of the bacteria in different components of the blood (white blood cells (WBCs), plasma or whole blood), using the above assays. The blood samples were obtained from the patients who were culture positive for S. aureus. Whole blood resulted in maximum PCR positives with sodA assay (90% positive) as opposed to cell-associated bacteria (in WBCs) (71% samples positive) or free bacterial DNA in plasma (62.5% samples positive). Both the assays were further tested for direct detection of S. aureus in patient whole blood samples that were contemporaneous culture positive. S. aureus was detected in 40/45 of culture-positive patients (sensitivity 89%, 95% CI 0.75-0.96) and 0/59 negative controls with the sodA assay (specificity 100%, 95% CI 0.92-1). CONCLUSIONS: We have demonstrated a highly sensitive two-hour assay for detection of sepsis causing bacteria like S. aureus directly in 1 ml of whole blood, without the need for blood culture.

Granular acute lymphoblastic leukemia in adults: report of a case and review of the literature.

The diagnosis of granular acute lymphoblastic leukemia (ALL) can be problematic as the cytoplasmic granules found in many blast cells may mimic those seen in acute myelogenous leukemia (AML). This rare variant of B-cell ALL is more commonly diagnosed in children, but may occur in adults. We report a case of granular B-ALL in a 56-year-old female and review the literature.

Prognostic significance of pronormoblasts in erythrocyte predominant myelodysplastic patients.

Recent studies of acute erythroleukemias have reaffirmed DiGuglielmo's syndrome (M6a, myeloblast-predominant) and disease (M6b, pronormoblast-predominant). M6c (mixed myeloblast/pronormoblast) has also been described. However, MDS is still defined according to the percentage of myeloblasts (% myeloblasts) without including the pronormoblast count. A 20-year retrospective study was performed to identify cases demonstrating >or=50% erythrocytic component and <30% calculated blasts (FAB exclusion criteria) without underlying cause (96 cases). Pronormoblast and myeloblast counts and other variables were analyzed as possible explanatory variables of the variations in survival. Considered alone, increasing % myeloblasts and/or percentage of pronormoblasts (% pronormoblasts) were significant predictors of decreasing survival. When all variables were considered as a multivariate group, the best fitting statistical model for predicting survival was a function of age, % pronormoblasts, IPSS cytopenias, platelet count, and percentage erythrocytic component. Of these, % pronormoblasts was by far the most significant. Nonappearance of % myeloblasts in this model is indicative of high correlations of this count with other variables.