Laboratory Medicine Update - 5/24/2001

University of Virginia Health System

Medical Laboratories

"Quality You Expect, Service You Deserve"

 

LABORATORY MEDICINE UPDATE

 

May 24, 2001

 

THINPREP PAP TEST NOW AVAILABLE

The Cytology Laboratory is pleased to announce the availability of the ThinPrep Pap test to all clinicians currently using the University of Virginia Pathology and Medical Laboratory Services. The ThinPrep Pap Test is a liquid-based methodology that can serve as a replacement for the conventional Pap smear in screening for abnormalities of the uterine cervix. It can reduce or eliminate many of the technical limitations of the conventional Pap smear, such as poor fixation, mechanical distortion, and excess blood/ inflammation. Studies have also shown increased detection rates for cervical abnormalities (LGSIL, HGSIL) when using this technology.

 

The clinical implementation of the ThinPrep Pap Test requires unique collection materials and a short instructional session on collection methods. The cellular sample is taken from the cervix/endocervix or vagina and placed directly into a preservative solution. The slides are then prepared in the laboratory using a special processing instrument. Clinicians will no longer need to make direct smears. The ThinPrep collection supplies and information about instructional sessions are available through the Cytology Laboratory.

 

The ThinPrep Pap Test has an increased cost over the conventional Pap smear, primarily due to the expense of the collection/processing kits. However, most major insurance providers, including QualChoice, Blue Cross/Blue Shield and Medicare, are giving an appropriately increased reimbursement for the test.

 

For additional information on this new service, on obtaining supplies or on arranging instructional sessions, contact our Customer Service Department at 4-LABS (434/924/5227).

 

 

SPECIMEN ACCEPTANCE POLICY - IMPLEMENTATION DATE CORRECTION

The last Laboratory Medicine Update indicated that the new Laboratory Specimen Acceptance Policy (Medical System Policy No. 00083) would become effective on June 1, 2001. This was incorrect. The actual implementation date is July 1, 2001.

 

 

VTE-d-dimer

 

The Clinical Core Laboratory will begin to offer the ELISA D-Dimer Assay (VTE-d-dimer) on May 22, 2001.

 

The VTE-d-dimer is intended for use only in the workup of deep venous thrombosis or pulmonary thromboembolic disease.

 

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  • The only value of the VTE-d-dimer is its negative predictive value in patients presenting with signs or symptoms suggestive of deep vein thrombosis or thromboembolic disease. In this setting, a VTE-d-dimer <500 μg/L has had an overall negative predictive value of about 97% for VTE.

     

 

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  • In patients with suspected pulmonary embolism, if the VTE-d-dimer is negative but the Wicki et al. clinical probability scoring system for pulmonary embolism is > 5 (Arch. Int. Med. 161:92, 2001), continue the workup for VTE.

     

 

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  • In patients with suspected DVT, if the VTE-d-dimer is negative, but the Wells et al. clinical probability scoring system for deep venous thromosis is > 1 (Lancet 350:1795,1997), continue the diagnostic workup for DVT.

     

 

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  • An elevated VTE-d-dimer has a poor positive predictive value for VTE. The diagnostic workup for VTE should continue when the VTE-d-dimer is elevated.

     

 

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  • A positive VTE-d-dimer does not establish the diagnosis of any form of VTE.

     

 

The above recommendations were established in collaboration with C. Edward Rose, Jr, MD and B. Gail Macik, MD. Please page the resident on-call for the Special Coagulation Laboratory at pic # 1663 with questions.

 

 

PSA TESTING METHODOLOGY CHANGE

 

 

On June 1, 2001, the Clinical Core Laboratory will implement a change in the Prostate Specific Antigen (PSA) method. The new assay is standardized to an equimolar (free vs complexed) PSA reference preparation. The purpose of the change is to improve the diagnostic performance of the assay in the "real world" environment of patient's specimens that contain various concentrations of different PSA isoforms. Based on the results of our evaluation of the new assay, no significant shift in values is expected compared to our current method. Also, sensitivity is improved, with the minimal detectable concentration being reduced from 0.1 to 0.05ng/ml.

 

To establish new baselines, at the request of the ordering physician, the Laboratory will perform method comparisons on individual patients until October 1, 2001 at no charge. Please indicate on the Requisition form that you would like to have both PSA assays performed. This comparison testing can also be ordered as an "add-on" within four days of submission of the specimen. The Laboratory report will contain the new assay result with the old method result listed as a comment.

 

Questions regarding the change can be addressed to Dr. Dan Haisenleder, Associate Director, Clinical Core Laboratory at Phone: 924-1149 or E-Mail: djh2q@virginia.edu.

 

 

Changes in FK-506 (Tacrolimus) values with changes in hematocrit

The Toxicology Laboratory has been notified by the manufacturer of the reagents used for the analysis of FK-506 (Tacrolimus) that changes in % hematocrit (HCT) can significantly alter the assayed value for this drug. Data published by the vendor suggest that an increase in HCT of 10% can result in an apparent reduction in drug level of up to 15%. The table below summarizes the study using two pools of EDTA-whole blood at various hematocrit values.

 

 

% Hematocrit

Tacrolimus Level (ng/mL)

Pool I

Tacrolimus Level (ng/mL)

Pool II

25

8.5

16.1

35

7.1

13.5

45

5.9

12.1

 

The manufacturer is continuing to work on this issue.

 

As with all therapeutic agents, Tacrolimus values should be interpreted in conjunction with information available from clinical evaluation and other diagnostic procedures.

 

NEW REFERENCE LABORATORY

 

Beginning July 2, 2001, the Medical Laboratories will begin using Quest Diagnostics as our primary reference laboratory. The decision to switch from American Medical Laboratories (AML) to Quest Diagnostics was made after a comprehensive review of the services, quality, and value offered by each of the major commercial laboratories.