University of Virginia Health System

University of Virginia Health System

Medical Laboratories

"Quality You Expect, Service You Deserve"

LABORATORY MEDICINE UPDATE

September 3, 2008

Stool cultures, slight change in protocol

Beginning 9-01-2008, the Clinical Microbiology laboratory will include an additional culture media for several non-enteric organisms in stool samples when a routine stool culture is ordered. This change is required to make the diagnostic algorithm consistent with standard practice in Clinical Microbiology. The previous routine stool culture was for the detection of Salmonella and Shigella species.  The new protocol will also include the recovery of Staphylococcus species, yeast and Bacillus species.  There will be an additional CPT code (87046) and cost ($56.00) added to the protocol.

If any additional organisms are suspected, as in the past, please special request them in case additional media need to be set up.  Examples are: Vibrio sp. or Yersinia sp.

Other enteric pathogens such as Campylobacter, Clostridium difficile Toxin A&B and Shiga Toxin can be ordered independently and are tested by EIA.  Cryptosporidium and Giardia should also be independently ordered.

MRSA screening protocols

For INPATIENT MRSA screening upon admission, please order only "MRSA Surveillance PCR", then select the specimen type, and schedule the collection.  Culture is not the preferred test for admission screening and should not be used.  "MRSA Surveillance Culture" should only be ordered under the direction of Hospital Epidemiology from an Infection Control Practitioner. 

Hospital Epidemiology has approved only the following specimen types for MRSA screening (whether done by PCR or culture):                            

• Nares Axilla Groin
• Scar (note location please) Throat Perirectal
• Ostomy

When the microbiology laboratory receives a specimen type other than those listed above, the test will be cancelled and the comment appended "Specimen does not meet the epidemiologic criteria for MRSA surveillance.  Please contact the laboratory (2-0460) within 24 hours if alternate testing is indicated".  Open wounds are not an acceptable specimen source and testing will not be performed if the specimen is labeled as a "Wound".  Healed wounds must be listed as "Scar" in the specimen description in order to be tested.  Please note the location of the scar being sampled.  Please consult Hospital Epidemiology if assistance is needed to obtain the appropriate MRSA screening protocol.

Change to Calculation for estimated Average Glucose from

Hemoglobin A_1C Value

The results of a comprehensive study by the A1c-Derived Average Glucose (ADAG) Study Group have been published in Diabetes Care¹.  The study followed 507 patients each of whom collected approximately 2700 individual glucose measurements (self-monitored) over a three month period of time.  Hemoglobin A_1c values were determined at the end of the study.  Linear regression analysis was used to derive a new recommended equation for estimating the average blood glucose concentration from the measured Hemoglobin A_1c result.  Age, sex, diabetes type, race/ethnicity, and smoking status were not found to contribute significant independent information over that provided by Hemoglobin A1c in estimating average blood glucose.

Medical Laboratories implemented the new equation on September 3, 2008.  The results of the new calculation are lower than those generated by calculations based on an earlier study².  A table of the 2002 calculation compared to the 2008 calculation follows.  Values above 12.0% Hgb A_1c are extrapolated from the study data.

¹Diabetes Care 31:1473, 2008.  http://www.ncbi.nlm.nih.gov/pubmed/18540046?dopt=Abstract

²Diabetes Care 25:275, 2002

Calculated Blood Glucose Based on Hgb A_1c

                                                                                                                                                Extrapolated Values