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C. Difficile Testing Update
C. Difficile Molecular Assay
CMMC Laboratory will be offering the Meridian illumigene® C. difficile NAAT molecular test, effective March 21, 2012. The test order name is “Clostridium difficile by Amplification” [C DIFF NAT].
Background In 2010, the Infection Disease Society of America, in conjunction with the Society for Hospital Epidemiology and the American Society for Microbiology, issued clinical practice guidelines for laboratory diagnosis of Clostridium difficile infections. Enzyme immunoassay (EIA) testing is no longer recommended for detection of C. difficile toxin in stool specimens due to the low sensitivity of these assays. Molecular testing is now considered the new gold standard of C. difficile testing. It combines significantly improved sensitivity with rapid results.
Methodology and Clinical Application The gene target is amplified by loop-mediated isothermal DNA amplification, called LAMP technology. This method is more expensive than the EIA test, but is more sensitive and will require only one sample to be submitted. Repeat testing is not recommended. Samples received within 7 days will not be processed without a pathologist’s or laboratory supervisor’s approval. The assay does not distinguish between viable and non-viable organisms. It is not intended to test for cure.
Patients should have 3 or more loose stools within 24 hours to qualify for C. difficile testing. The Illumigene test is also FDA approved for children under the age of 2 years.
03/16/2012
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Beta-hydroxybutyrate
New test for serum ketones
Written by John W Skinner, MD January 30, 2012
Effective immediately, methodology for serum ketones has been changed to a new, quantitative test measuring beta-hydroxybutyrate in whole blood (sometimes abbreviated as â-OHB). The new test will be called â-ketone, and the test previously called ketone representing a nitroprusside test will be removed from the menu of lab tests.
Beta-hydroxybutyrate is one of three blood ketone bodies and represents about 75-78% of ketone bodies, with acetoacetate and acetone representing about 20% and 2% respectively. The nitroprusside test measures only acetoacetate and to a lesser extent acetone but does not measure beta-hydroxybutyrate. Since the nitroprusside test does not measure the predominant ketone fraction in ketoacidosis, it is considered less sensitive to the detection of the early stages of ketoacidosis when compared to the measurement of beta-hydroxybutyrate.
Venous blood for the â-ketone test should be collected in a sodium heparin (green top) tube and analyzed within 30 minutes.
Numerical results will be reported, up to 8.0 mmol/L, and higher results will be reported as >8.0 mmol/L. The normal range for â-ketone in healthy subjects is less than 0.5 mmol/L. Values of â-ketone between 2.0 - 4.0 mmol/L roughly correlate with moderate serum ketone by the traditional nitroprusside test.
01/30/2012
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