Laboratory Medicine Updates - January 26, 2007

University of Virginia Health System

Medical Laboratories

"Quality You Expect, Service You Deserve"

 

LABORATORY MEDICINE UPDATE

January 26, 2007

Change in Reporting of Estimated GFR

In keeping with national guidelines, estimated GFR will no longer be reported numerically when it is greater than 60 mL/min/1.73 m2.  Reports will indicate "> 60". Estimated GFR is calculated by use of the MDRD equation which is based on data from patients with GFR < 60 mL/min/1.73 m2; the equation does not produce valid estimates at higher values of GFR.

For information on calculated GFR, see

1. Stevens LA, Coresh J, Greene T, Levey AS. Assessing kidney function--measured and estimated glomerular filtration rate. N Engl J Med 2006; Jun 8;354(23):2473-83. http://content.nejm.org/cgi/content/full/354/23/2473 (accessed 18 January 2007)

2. National Kidney Foundation. Kidney learning system.  http://www.kidney.org/professionals/KLS/gfr.html#8 (accessed 18 January 2007).

 

Virginia State Newborn Screening

Virginia statutes require that all newborns be screened for a panel of 28 disorders through submission of dried blood samples to the State Lab.  In an effort to make this mandate as beneficial and cost effective as possible, results of testing submitted after January 18, 2007 will be available in the electronic medical record as a routine laboratory result.  In CareCast, the results will be found under Chemistry.  It is hoped that unnecessary duplicate testing will be reduced through easier access to the results.

Specimens must be collected on a State card ("PKU card") and must be collected when the infant is more than 24 hours old and before a blood transfusion.  There are no longer restrictions due to antibiotic use.

All information requested on the card must be completed.  Please be aware that each card costs $53, regardless of whether or not it is used for testing (testing itself is at no charge).  Your assistance in preventing waste will be greatly appreciated.

 

4 a.m. Collection Lists:  Timed vs. Routine

The Medical Laboratories phlebotomy team has experienced a large increase in the number of routine labs ordered as "timed" collections for the 4 a.m. rounds.  The 4 a.m. collection list is intended for specimens that medically require collection at that specific time.  With limited staff collecting samples on the acute care units at 4 a.m., adding routine samples to this list impedes the phlebotomists' ability to collect all samples in a timely manner.  Additionally, many patients have routine orders placed appropriately for the 6 a.m. list and are, consequently, being drawn twice for routine orders.  This will not affect patients pending discharge who should have labs ordered in the MIS discharge pathway to ensure availability of results by 7:30 a.m.

We appreciate your attention to this matter and believe that by following these practices, we will provide better patient care and patient satisfaction.

 

Anal Cytology - Specimen Collection and Submission for Laboratory Testing

Cytologic evaluation of samples from the anal canal has been shown to be of value in the detection of squamous cell carcinoma of the anus and its precursor lesions for both male and female populations considered at risk for this disease. These anal lesions are associated with the sexual transmission of oncogenic HPV types. The Cytology Laboratory is now offering anal cytology evaluation with and without reflex oncogenic HPV testing.

Materials:

  • Water-moistened Dacron swab or cytobrush
  • Preservcyt vial for liquid-based cytology (obtained from the Cytology Laboratory)
  • Patient label
  • Cytopathology Request Form or Cytology Lab order in CareCast

Specimen Collection:

  1. Goal: to sample the entire anal canal, including the transformation zone up to the distal rectum.
  2. Insert a water-moistened Dacron swab or cytobrush into the canal about 5-6 cm above the anal verge and into the distal rectum.
  3. Using the external anal sphincter as a fulcrum, rotate the swab in a cone-shaped arc, applying pressure to the canal walls as the device is withdrawn.
  4. Rinse the material into the Preservcyt vial by agitating the swab or brush several times in the solution. Label the specimen vial with patient label.
  5. Complete a Cytopathology Request Form or a CareCast order with all necessary information.

To order the test on the request form, check "Other" under NON-GYN Cytology and write in "anal swab" or "anal brush".  Please indicate if reflex HPV testing is also desired.

When ordering in CareCast, select Non-Gynecologic Cytology under test order and then choose either "Anal Brush/Swab" or "Anal Brush/Swab with HPV testing" from the list of specimen types. Print a copy of the CareCast order to submit with the specimen vial.

  1. Submit the specimen vial with the paperwork to the Cytology Laboratory for processing.

If you require additional information or have any questions about this test, please contact the Cytology Laboratory at 924-2770.

 

New Reference Intervals for Coagulation Tests

The Coagulation Laboratory will update the reference intervals for the following assays on February 1, 2007.  This is an annual adjustment due to a change in the lot number of coagulation reagents, and the ISI value involving the PT reagent specifically.

The new reference ranges are as follows:

  • Prothrombin Time (PT) = 11.9 - 15.2 seconds, new ISI value = 1.22 with a geometric mean of 13.5 seconds.
  • Activated Partial Thromboplastin Time (aPTT) = 24.1 - 35.8 seconds.
  • Heparin Therapeutic Range for unfractionated heparin aPTT values is 64 - 102 seconds corresponding to 0.3 - 0.7 Anti-Xa Units/mL.

Any questions may be directed to the Special Coagulation Laboratory at 924-8007 or by paging the Pathology Resident for Coagulation at pic 1663.

 

NKX2.5 Gene Sequencing

Congenital heart defects (CHD) affect up to 1.0% of all live-births and are the most common birth defect.  The majority of these are non-syndromic CHD.   Though a large number of these are due to genetic defects, there are only a few genetic tests available for the work-up of individuals with CHD.  These are primarily karyotype analysis and DiGeorge (22q) deletion analysis, which have a combined pick up rate of about 5%.  Thus a large number of CHDs are left without an etiology.

In order to increase the diagnosis rate in cases of CHD, we have been developing new genetic tests for CHD.  We have now developed a sequence based test for mutations in the NKX2-5 gene (NK2 transcription factor related, locus 5 (Drosophila), also called NKX2.5).  This gene is found on human chromosome 5q34 and consists of only two exons.  The NKX2-5 gene encodes a cardiac transcription factor that is expressed in the developing heart and plays a central role in cardiac differentiation and development.  Mutations in the gene have been associated with non-syndromic CHD in humans.  The NKX2-5 mutations identified in families are inherited in an autosomal dominant manner.  Heterozygous mutations were identified in families with progressive atrioventricular (AV) conduction block and secundum atrial septal defect (ASD) as well as other structural heart defects.  The estimated detection rate of NKX2.5 mutations in cases of familial ASD and AV conduction block is based on several small studies, but is expected to be as high as 70-80%.  Of note, the estimated frequency of NKX2-5 mutations in sporadic CHD (the most common form of CHD) is about 3-4%.  This almost doubles the pick-up rate for genetic defects in CHD when used in conjunction with cytogenetic analysis.

To identify NKX2-5 mutations, the entire coding region and immediate flanking regions of the NKX2-5 gene are amplified by PCR and sequenced in both the forward and reverse directions.  The DNA sequence is then compared to a normal reference sequence to identify sequence variants.  Sequence variations are compared with known NKX2-5 mutations to determine if the variation is a novel or a previously reported mutation.  Over 20 mutations have now been identified in the NKX2-5 gene by direct sequence analysis.  These are associated with either ASD and cardiac conduction defects or other structural heart defects.

Indications for testing:  Sequencing of NKX2-5 is appropriate for a person with a family history of ASD and AV conduction block.  The detection rate in such cases may be as high as 75%.   NKX2-5 mutations may also be found in persons with sporadic ASD or other structural heart defects, such as tetralogy of Fallot, but the detection rate in these cases is expected to be about 3-4%.

Beginning February 1, 2007, the Clinical Microbiology and Molecular Diagnostics Laboratory will perform NKX2-5 gene mutation analysis on whole blood specimens collected in lavender top (EDTA) tubes. A consultation request form with indications for testing should accompany the specimen. The test code is NKX25 and the charge is $603. The turnaround time is four weeks and an interpretive report (CoPath) will follow and be available in CareCast under Pathology, Molecular Diagnostics.