Laboratory Medicine Updates - November 30, 2006

University of Virginia Health System

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LABORATORY MEDICINE UPDATE

November 30, 2006

Peptide Nucleic Acid-Fluorescent In Situ Hybridization (PNA FISH)

For organisms in blood culture

Beginning December 11, 2006, Clinical Microbiology will perform the PNA FISH test on blood cultures that become positive with gram positive cocci or yeast.  The test will be performed twice a day Monday through Friday and once a day on weekends and holidays. Results will be reported by noon and by 6 PM (depending on the time of detection of the positive blood culture). The PNA-FISH test definitively distinguishes Candida albicans from non-C. albicans, Staphylococcus aureus from non-S. aureus and Enterococcus faecalis from non-E. faecalis. Enterococcus species that are not E. faecalis are also detected but will not be speciated at the time of the report.  The main advantage of this test is a decrease in time to species identification, which consequently may allow antimicrobial management to be tailored to less toxic and less expensive or more appropriate agents.

 

Tissue Samples for Microbiological Analysis

When submitting tissue samples for microbiologic analysis, please transport the specimen in a sterile leak proof container such as a sterile urine cup.  The ideal size of the tissue should be between pea and marble size.  Smaller pieces may not provide enough specimen for adequate media inoculation and the Clinical Microbiology laboratory does not have the equipment to process larger pieces.  Do not send entire body parts to the microbiology lab. These specimens should be sectioned and only the pieces from the site of infection should be sent for analysis.

 

HCV Viral Load Testing

The UVA Clinical Microbiology and Molecular Diagnostics Laboratory is now performing HCV viral load testing (quantitative HCV analysis) with the Roche Diagnostics TaqMan Analyte Specific Reagent (ASR) method.  This real-time PCR method has an expanded dynamic range for quantification (50 - 5 million IU/mL) compared to the Roche Amplicor HCV Monitor Test (version 2.0) it replaces.  The new assay requires a minimum of 0.5 mL serum.  Quantification of viral loads above 5 million IU/mL is possible by dilution; however, a second test order will be required.

 

HIV Viral Load Testing

The UVA Clinical Microbiology and Molecular Diagnostics Laboratory has updated the HIV viral load procedures to include automated specimen processing by the Roche COBAS AmpliPrep instrument.  The required specimen for testing is EDTA (lavender top) blood.  A minimum volume of 0.7 mL plasma is required for ultra-sensitive viral load analysis and at least 0.25 mL plasma is required for standard viral load testing.  This is an increase over previous specimen volume requirements.  The linear range of the standard quantitative assay has expanded to 400 - 1 million copies/mL, but the range of the ultra-sensitive test remains 50 - 100,000 copies/mL.

 

HIV Genotyping and Resistance Reporting

Resistance interpretation (correlation of Protease and RT sequences to antiretroviral drug resistance) is based on interpretation of in vitro and in vivo phenotypic and virologic response data by The Consensus Panel, an international expert panel.  These include both primary and secondary mutations.

GuideLines Rules 11.0, using data available as of July 2005, is now available and will be applied to the Bayer TruGene HIV-1 Resistance reports.  Highlights of the new interpretation rules include:

  • o Zalcitabine (ddC) has been removed from the list of Nucleoside and Nucleotide RT Inhibitor drugs
  • o Protease Inhibitor Rules for Ritonavir boosting of Atazanavir (Atazanavir + Ritonavir (ATV/r) have been added

The next version of the GuideLines is tentatively due for release in March/April 2007.

 

Drawing of Timed Cortisol Specimens

In agreement with the Managers of the Acute Care Units, timed cortisol collections (that is, specimens that must be collected at specific times following an injection of ACTH to measure cortisol suppression) will be the responsibility of the unit.  This change is to insure that the laboratory phlebotomy team is available for timely routine blood draws.

 

Specimen Collection through an In-dwelling Line

Please remember that the correct procedure for collecting a blood specimen through an in-dwelling line involves stopping the infusion for at least five minutes and collection of a 10 mL discard specimen (particularly in the case of a heparin lock) prior to collecting the sample for analysis.  Failure to follow this protocol often results in contamination of the blood specimen with the solution being infused and can lead to inaccurate test results.

 

New Hematology Equipment for the Core Laboratory

On October 24, 2006, the Hematology Division of the Core Laboratory began testing with new analyzers, the Sysmex XE-2100.  This transition should have been invisible to the clinical staff but provides the following advantages:

  • Faster analysis per sample so a reduction in Turn Around Time
  • Overall reduction in manual slide review and subjective slide interpretation
  • Reduction in the need for phase (manual) platelet counts so a reduction in Turn Around Time
  • Corrects WBCs for NRBCs and interfering particles
  • Allows for the enumeration of immature granulocytes

Compatible equipment is planned for implementation in the Cancer Center.