Laboratory Medicine Updates - 10/4/2000

 

University of Virginia Health System

Medical Laboratories

"Quality You Expect, Service You Deserve"

 

LABORATORY MEDICINE UPDATE

 

October 4, 2000

THROAT CULTURES

 

The Clinical Microbiology Laboratory has recently changed its protocol for screening and reporting throat cultures. Streptococcus equisimilis has been documented to cause similar symptoms and sequelae to Group A Strep. As a result, the lab will now routinely screen all throat cultures for Group A beta strep as well as S equisimilis. No change in ordering or specimen collection is necessary.

 

 

SUSPECTED BACTERIAL PATHOGENS

 

Reminder: If a microbiology specimen is submitted to the laboratory and particular pathogen is suspected, please notify the lab by phone or indicate on the test request forms. Many organisms require special processing in order to obtain growth. For example, Malassezia spp. require lipid. Therefore, communication with the laboratory is essential.

 

 

STERILE BODY FLUID CULTURES

 

Sterile body fluids should be submitted in sterile tubes for optimal organism recovery and reporting. The use of blood culture bottles for sterile body fluid culture is not recommended. If fluids are submitted for culture in blood culture bottles, they will not be gram stained. No quantitation can be made if growth becomes evident. Please refer to the following web site for more information on the submission criteria for sterile body fluids.

 

http://hsc.virginia.edu/medcntr/med-management/lab/hottopic/fldspec0002.html

 

 

REFERRAL TESTING CHANGES

 

  •  

  • Specimens submitted for Neurontin analysis: red top tube with no additive (7 mL tube).

     

     

  • Specimens submitted for CMV Antigenemia analysis: 7 mL lavender top EDTA tube.

     

     

  • Hemosiderin is now a referral laboratory test. Result turn-around-time for this test is 48 to 72 hours.

     

 

 

Fibrin Split Products (FDP) Assay

 

Due to changes in reagent availability from the manufacturer, the Fibrin Split Products Assay (FDP) has changed from a serum-based assay to a plasma-based assay. The same sodium citrate tube (blue top) acceptable for all other coagulation assays is now to be used for this assay. There is no change in the test order code (FDP). The new reference interval is < 5 ug/mL.

Please contact the Special Coagulation Laboratory at 4-8007 if you have questions.

 

 

Acceptable Tube Types For Coagulation

 

The Laboratory requests that 4.5 mL sodium citrate Vacutainer tubes (blue top tubes) be used on a routine basis for any coagulation testing. The 1.8 mL blue tops should only be used for pediatric patients, oncology patients, or other compromised patients who pose a very difficult venipuncture situation requiring smaller blood volumes.

 

If your area has only the 1.8mL tubes in stock, please replace these with the 4.5 mL blue-top vacutainer tubes. Use storeroom bin number 92493 to order the 4.5 mL blue top Vacutainers.

 

 

Endocrinology Reference Intervals

 

New Pediatric Reference Intervals are now available for the following tests:

 

Test

Age Interval

Reference Interval

Total T3

1 - 3 days

89 – 405 ng/dL

4 days - 1 month

91 – 300 ng/dL

1 - 12 months

85 to 250 ng/dL

Over 1 year

60 – 200 ng/dL

T4

1 - 3 days

8.2 – 19.9 µg/dL

4 days - 1 month

6.0 – 15.9 µg/dL

1 - 12 months

6.1 – 14.9 µg/dL

Over 1 year

4.5 – 10.9 µg/dL

Free T4

0 - 3 days

2.0 – 4.9 ng/dL

4 days - 12 months

0.9 – 2.6 ng/dL

Over 1 year

0.8 – 1.8 ng/dL

TSH

Under 1 year of age

TSH surges within the first 15-60 minutes of life, reaching peak levels (25-160uU/mL) at 30 min. Values then decline rapidly and after 1 week are within the adult normal range.

CMV IgG testing

 

Due to changes in CMV IgG reagent formulation, the reference intervals for this test are as follows:

 

Negative <10 AU/mL

Equivocal* 10 – 14.9 AU/mL

Positive >15 AU/mL

 

*It is recommended that equivocal results be followed with repeat testing in one to three months.

 

 

Reflex Testing for Thyroid Function

The University of Virginia Laboratory Utilization Committee and the Division of Endocrinology and Metabolism recommend that for most ambulatory patients, TSH alone should be used as the initial test to exclude hypothyroidism and hyperthyroidism. If TSH is abnormal, free T4 should be run on the same sample. Beginning November 1, 2000 these tests can be ordered as "TSH Reflex". It is important to point out, that TSH reflex testing may be misleading with the diagnosis of secondary or tertiary thyroid disease (<5% of patients with thyroid disorders). Therefore, if pituitary or hypothalamic disease is clinically suggested, both TSH and free T4 should be ordered.

 

For more information regarding this recommendation, please contact Dr. Alan Dalkin at (434) 924-1148.