Laboratory Medicine Updates - August 31, 2005

University of Virginia Health System

Medical Laboratories

“Quality You Expect, Service You Deserve”

 

LABORATORY MEDICINE UPDATE

August 31, 2005

24 Hour Phlebotomy

Starting at 04:00 on September 1, 2005 , the Medical Laboratories will assume responsibility for night shift phlebotomy service.  Between 22:01 and 05:59 , the Medical Laboratory Phlebotomy team will collect all “Timed” requests.   This means that phlebotomy will be making sweeps through the units to collect previously ordered timed specimens at 2400, 0200 and 0400.  Historically, the majority of labs requested on nights have been ordered STAT.  Unless results are required on a stat basis, any lab needed on nights should either be ordered as timed to be collected at the next time point or ordered for routine collection.  The existing service will continue to operate as normal during the 06:00 to 22:00 time frame.   Please note that any order placed as “routine today” after 22:00 will be collected by the lab on the 06:00 collection list.

STAT priority specimens remain the responsibility of the caregiver.  The IV team will not be available for any timed lab collections beginning September 1 at 04:00 , but will continue to be available to assist with STAT requests on nights.  Unit personnel may continue to call the Phlebotomy team for assistance if necessary, but response time will be dependent on current workload and staffing.

 

Change to BNP Test

The Chemistry Division of Medical Laboratories has moved BNP testing from a manual platform (Bio-Site Triage) to an automated platform (Abbott AxSym).  Comparative testing between these two platforms showed slope of ~1.15 (x = Bio-Site, y = AxSym), similar to published reports1.  The move to the new analyzer will allow testing of specimens up to 24 hours after draw (EDTA tube, purple top) as long as the specimen is kept cool.  For specimens that cannot be submitted to the laboratory within 1 hour of draw, please hold/submit on wet-ice.  The new platform also allows for reporting of results of up to 20,000 pg/mL.

1Rawlins, Owen, and Rob erts.  Performance Characteristics of Four Automated Natriuretic Peptide Assays.  Am J Clin Pathol 2005;123:439-445.

 


The Cytology Laboratory Implements Computer-Assisted Screening for

ThinPrep Pap Tests

The Cytology Laboratory is pleased to announce the implementation of the ThinPrep Imaging System (Cytyc Corporation, Boxborough, MA), which is a FDA-approved automated system that assists cytotechnologists with the primary screening of ThinPrep Pap test slides. The Imager is a device that combines computer imaging technology with human microscopic review and interpretation. Each ThinPrep Pap test slide is initially screened by the imager searching for the most likely abnormal cells and locates these cells for evaluation and interpretation by the cytotechnologist. This allows the cytotechnologist to spend less time on the process of screening and focus on the challenge of evaluation and interpretation of the unusual cellular findings identified by the Imager.

Clinical trials of the Imaging System showed improved diagnostic sensitivity over manual screening for “atypical squamous cells” and equivalent sensitivity for both high-grade and low-grade squamous intraepithelial lesions. In addition, as we gain experience with the instrument, we anticipate improved turn around times as this technology enables us to increase the number of cases we can process without sacrificing the sensitivity and specificity of disease detection.

One of the primary goals of the Cytology Laboratory is to provide timely, consistent and accurate Pap test interpretations to enhance quality patient care and allow for appropriate ancillary testing when needed. The introduction of the ThinPrep Imaging system is a major step forward in helping to insure the achievement of these goals.

 

Reference Intervals for Potassium and Phosphorus in Serum and Plasma

Reminder:  The reference interval for potassium in plasma is 3.5-4.5 mmol/L in males and 3.4-4.4 mmol/L in females1.  See the Lab Medicine Update of June 7, 2005 .  For serum specimens, the reference interval is slightly higher due to release of K from platelets and cells during the clotting process in vitro:  3.5-5.1 mmol/L. 

A similar difference in the reference intervals for phosphorous is seen between plasma and serum samples.  For plasma samples, as used for almost all testing at the University of Virginia, the reference intervals are:

Age                  Reference Interval
0-6D                4.5-9.0 mg/dL
7D-24M          4.5-6.7 mg/dL
24M-12Y        4.5-5.5 mg/dL
12Y-18Y         2.3-4.7 mg/dL
­>19Y               2.3-4.7 mg/dL

Serum samples will be ~0.2 mg/dL higher for all age groups.

1Burtis CA, Ashwood ER, Bruns DE. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics.  St. Louis : Elsevier Saunders, 2006.


Change in Creatine Kinase reference interval

The study upon which UVA’s presently-reported reference intervals for CK are based1 employed only Caucasian European reference subjects.  A study carried out at MCV2 better reflects the Virginia population and shows the age-related changes that occur in CK (see figure below).  Based upon the latter study, the upper reference limit for CK in males is being changed from 200 U/L to 300 U/L to reflect values likely to be seen in the older population of interest.  The reference interval for females will remainunchanged.

CPK_ref_range_graph

Figure from Miller et al.2.

1 Franck PF, Steen G, Lombarts AJ, Souverijn JH, van Wermeskerken RK. Multicenter harmonization of common enzyme results by fresh patient-pool sera. Clin Chem. 1998;44:614-21.

2 Miller WG,  Chinchilli VM, Gruemer HD, Nance WE. Sampling from a skewed population distribution as exemplified by estimation of the creatine kinase upper reference limit. Clin Chem 1984;30:18-23.

 

Correction – Mayo Medical Laboratories On-Line Test Catalog

The correct web address for May Medical Laboratories on-line test catalog is:

http://www.mayomedicallaboratories.com