Laboratory Medicine Updates - March 19, 2004
University of Virginia Health System
“Quality You Expect, Service You Deserve”
LABORATORY MEDICINE UPDATE
March 19, 2004
Stool Osmolality No Longer Available
This test has been discontinued by our Referral Laboratory Quest Diagnostics. It is suggested that Stool Sodium and Stool Potassium be ordered as replacement tests. Any questions can be directed to the Referral Desk at 982-4051.
Change in Reference Interval for Fasting Glucose
To adhere to current (January 2004) American Diabetes Association guidelines, the reference intervals for fasting plasma glucose (FBG) have been change to 70 – 100 mg/dL for those over 12 years of age and 60 – 100 mg/dL for those 12 and younger.
Verification of Insurance
As a result of recent Federal legislation, clinical laboratories based in hospitals no longer need to complete the Medicare as Secondary Payor Questionnaire when performing tests on patients referred by community physicians. Accordingly, Medical Laboratories staff will no longer call reference lab patients to verify whether Medicare is their primary payor. However, Medicare law still requires that Medical Laboratories only bill Medicare when Medicare is primary. It is important, therefore, that information regarding patients’ insurance coverage furnished by referring physicians be accurate. Since Medical Laboratories will be relying solely on the information received from referring physicians, please be sure to compare information furnished to Medical Laboratories against information contained in the billing records for each referred patient. In addition, when multiple payors are listed, they should either be in the order of billing priority or indicated as primary and secondary.
Ciliary Motility Studies Now Available – Cytopathology Laboratory
Immotile cilia may be responsible for a variety of problems, including upper respiratory infections that are unresponsive to therapy. The Cytology Laboratory is now offering kinetic studies of fresh cellular material in brushing samples from the nasal turbinate to assess the motility characteristic of living cilia. Once kinetic studies are completed, the remainder of the brushing sample is processed for electron microscopic studies to identify the presence or absence of structural abnormalities in the cilia. For information about specimen collection, test ordering and results reporting, contact the Cytology Laboratory at 924-2770 or 924-2779.
Change in Procedure for Fragile X Analysis – Molecular Diagnostics Laboratory
Fragile X syndrome, a common cause of inherited mental retardation, is caused by expansion of a (CGG)n trinucleotide repeat within the 5’-untranslated region of the fragile X mental retardation 1 (FMR1) gene on Xq27.3. The current procedure involves DNA extraction, digestion, gel separation, transfer to a solid membrane, and analysis of the membrane using DNA probes (Southern Blot). The data generated is at the level of normal, premutation, and full expansion only. The new procedure involves DNA extraction and PCR followed by fragment-size analysis by capillary electrophoresis; the fragment-size analysis is then mathematically converted to the number of CGG repeats. The new procedure allows for the specific number of repeats to be determined within +/- 2 repeats. Patients with fragile X syndrome have expansions >200 CGG repeats. The presence of 55-200 CGG repeats indicates a premutation allele. Normal individuals have between 5 and 44 CGG repeats, with 30 repeats being the most common number of repeats. A “grey zone” exists between 45 and 54 CGG repeats, where individuals are clinically unaffected, but are rarely predisposed to passing on a premutation to their offspring.
Males with premutation alleles pass these to their daughters relatively unchanged in size. Premutation alleles in females can expand into full mutations in their children and larger premutations (>90 repeats) are more likely to become fully expanded.
There is now evidence that the premutation alleles themselves have clinical correlates, including premature ovarian failure (POF) among female carriers and a fragile X-associated tremor/ataxia syndrome (FXTAS) among older male carriers. Nearly 1 in 800 men in the general population is a carrier of the fragile X premutation and research suggests that as many as 30% of carriers (1 in 3,000 men) may develop FXTAS later in life. Approximately 1 in 250 women are carriers of the fragile X premutation. Based on recent studies, approximately 21% of female premutation carriers have POF compared to only 1% in the general population. Studies looking at all women with POF suggest that approximately 5 to 6% are positive for the fragile X premutation. The new procedure will be helpful in making these diagnoses.
A caveat to the new method is that it will only be useful for expansions up to ~90-100 repeats. Beyond that number, the PCR reaction fails and samples will need to be analyzed by Southern Blot. So, women with only one detectable allele or men with no detectable allele by PCR will still need to be analyzed by Southern Blot. However, it is expected that approximately 90% of the samples submitted will be successfully analyzed with the new method, leaving only 10% that will require repeat analysis by Southern Blot. Because some specimens will require Southern Blot analysis, the turnaround time will remain four weeks, but in most cases results will be available much sooner. There will also be a slight price increase (from $339 to $360) associated with the new procedure. A 5mL EDTA blood specimen and Consultation Request Form with relevant clinical history are required for analysis.