University of Virginia Health System
Medical Laboratories
“Quality You Expect, Service You Deserve”
LABORATORY MEDICINE UPDATE
March 29, 2011
QUAD Testing (2nd Trimester Screen)
In order to perform accurate statistical analysis for 2nd trimester QUAD pregnancy screening, it is imperative that all the information requested be provided. Significant non-compliance has been seen with electronic orders entered into EPIC from the clinics. The most common errors are failure to provide:
· Race of the patient
· Maternal date of birth
· Dating either by last menstrual period (LMP) or ultrasound (US)
Your attention to these details will allow more timely reporting of results.
Genetic Testing for Coagulation Disorders
The Molecular Diagnostics Laboratory continues to see separate orders for analysis of Factor V (Leiden) and Prothrombin Gene (Factor II) mutations. When this occurs, the laboratory must cancel the two orders and re-order the Thrombophilia Panel for compliance reasons. This panel is available in Epic and can be found by typing in “Thrombophilia Panel, DNA” (or a portion of the name). Please contact the laboratory at 982-3310 if you have any questions.
Comparative Genomic Hybridization Testing
The Cytogenetics Laboratory offers CGH testing. Currently this assay is not orderable in EPIC but a request has been made to add it to the test list. You may use the Cytogenetics test request form during the interim since it prompts for the required information.
There are two important issues to keep in mind when ordering this assay.
· Specimen requirements are 1 purple (EDTA) tube and 1 dark green (Sodium Heparin) tube. Tubes are available from the laboratory (4-5227) if they are not on the floor. Please note the specimen is a dark green tube and not the light green (lithium heparin) associated with general chemistry tests.
· Patient history and reason for requesting the assay (mental retardation, developmental delay, autism, dysmorphic features, failure to thrive, or multiple congenital anomalies) along with the appropriate ICD-9 code must be provided.
Post-Discharge Laboratory Reports
Laboratory Computing will no longer print and deliver laboratory reports for testing that is resulted after discharge. All results can be found in the Epic system.
Epic Tips for Laboratory Orders
The laboratory continues to receive samples with paperwork from EPIC that are not coming across the interface to the laboratory’s computer system. Generally there are three reasons that the lab cannot see the orders:
· the order needs to be statusedas“collected”underpatient summary
· the order has to be signed in EPIC. If the order is not under Chart Review (lab tab) most likely it has not been placed or it has not been signed.
· thepatient must be assigned to the correct patient unit locationin Epic when the order is placed to follow the correct collection rules.
New HIV Ab/Ag Test
The Medical Labs has implemented a new HIV EIA test. The Architect HIV Ag/Ab Combo is a fourth-generation assay that detects IgG and IgM antibodies to HIV-1 and HIV-2 as well as the p24 antigen (the most abundant protein of HIV virions) which is often produced earlier during infection than anti-HIV antibodies.
Results will be reported as “reactive” or “non-reactive”. The test does not differentiate between reactivity to the p24 antigen, to antibodies to HIV-1, or to antibodies to HIV-2. Therefore, additional testing is required to distinguish HIV-1 from HIV-2 and acute HIV infection from established HIV infection. Reflex testing will be performed automatically on samples with reactive or indeterminate results. The initial test will be HIV-1 Western Blot. Specimens with a negative HIV-1 Western Blot will be sent to Mayo Medical Laboratories for HIV-2 testing by Western Blot.
Tests for antibody alone do not allow identification of acutely infected individuals who have not yet begun to produce HIV-specific antibodies and who are at greatest risk for transmission of the virus. In acutely infected patients with detectable HIV RNA, the Combo assay was reactive in 86% and 89% of patients with negative third-generation immunoassays and negative rapid point-of-care tests, respectively (Pandori 2009).
Studies performed by the vendor demonstrated the specificity of the assay in a low-risk population to be 99.77%. The antigen and antibody sensitivities were found to be 100% to HIV-1 groups M, N, O and HIV-2. A study of seroconversion panels demonstrated that the Architect Ab/Ag Combo reduced the time to detection by a median of 7 days compared to the FDA-licensed HIV 1/2/O Antibody assay. In pregnant females at increased risk for infection, the sensitivity and specificity both were found to be 100%. In a pediatric population, the sensitivity and specificity were 100% and 99.83%, respectively (all data from Architect HIV Ag/Ab Combo package insert).
It is important to note that while the Ag/Ab combo test will reduce the window period after infection, it does not eliminate it. If there is clinical concern for acute HIV infection after recent risky exposure and the EIA result is negative, repeat testing of the patient is encouraged.
References:
Pandori MW, Hacket JJ, et al. Assessment of the ability of a fourth-generation immunoassay for human immunodeficiency virus (HIV) antibody and p24 antigen to detect both acute and recent HIV infections in a high-risk setting. Journal of Clinical Microbiology 2009; 47(8): 2639-2642.
Branson BM. The future of HIV testing. Journal of Acquired Immune Deficiency Syndrome 2010; 55(S2): S102-S105.
Chlamydia trachomatis and Neisseria gonorrhoeae: New Guidelines
New treatment guidelines for sexually transmitted diseases were recently released from the CDC. Considerations for the diagnosis of infections with Chlamydia trachomatis (Ct) and/or Neisseria gonorrhoeae (Ng) have been updated as a part of these guidelines. Please refer to http://www.cdc.gov/std/treatment/2010/STD-Treatment-2010-RR5912.pdf to review the guidelines in their entirety. The UVa laboratory’s recommendations and strategies for Ct and/or Ng testing (only) are addressed as follows:
1. Testing of specimens from the urogenital tract of men and women will continue to be performed in the UVa laboratories.
- The FDA-approved assay utilized at UVa has a high negative predictive value for appropriately collected and transported samples (approximately 99.7% for both Ct and Ng in our low-prevalence population).
- The Ct/Ng tests are for use only with endocervical, urethral, and urine specimens. Male urethral specimens from asymptomatic patients and female urine specimens demonstrate reduced performance with these tests; therefore, endocervical samples are the specimen of choice for females and urine is the specimen of choice for asymptomatic males.
- These tests are not intended for use with throat, rectal, or other types of specimens. Performance characteristics for non-urogenital specimens have not been studied at UVa.
- Specimens other than urine should be submitted in CTM, M5, M4 or M4RT transport.
- False positive results can occur. The PCR assay used by UVa laboratories (and others) is known to cross-react with non-pathogenic Neisseria spp rarely found in the genital tract. Additionally, prevalence of Ct and Ng is very low in our patient population (approximately 4.0% and 1.5% respectively). Because of these low prevalence rates, the assays have a high negative predictive value (NPV 99.7%) but a poor positive predictive value (PPV), which may be as low as 60% for Ct and 40% for Ng. Clinicians are encouraged to review treatment guidelines in this setting and counsel patients regarding the risk vs benefit of therapy in the presence of a potential false positive test. Retesting using culture methods can be performed to improve PPV, but clinicians must consider the risk of a false negative result in this setting.
2. The 2010 guidelines support testing rectal and throat samples for Ct and Ng in patients at risk of infection at these sites. Please review the guidelines for considerations in specific populations at risk.
a. Ct nucleic acid testing or culture on non-urogenital samples can be performed on samples submitted in M4 or M5 transport media.
1) Please order “C. trachomatis DNA – nonurogenital”. This will generate a Miscellaneous Send-out request. Please type “Ct DNA and state the site of collection (rectal, throat, eye).
2) This test request will temporarily generate a request for Pathology Resident approval if ordered on inpatients. We apologize for this inconvenience. A new test code specific to non-urogenital samples has been requested. Clinicians will be notified when this order option is available.
3) Culture for C. trachomatis can be ordered as a miscellaneous send-out, stating Ct culture and the site of collection. .
4) Expected turn around time from our reference laboratory is 3 days for DNA testing and 7 days for culture.
b. Nucleic acid testing is NOT available for Ng at non-urogenital sites with our current collect/transport devices.
1) Please order only culture for non-urogenital sites and specify rule out of Neisseria gonorrhoeae.
2) Samples should be collected with culturette swabs and submitted to the laboratory within 2 hours of collection to ensure appropriate sensitivity.
- In all cases of neonatal conjunctivitis, conjunctival exudates should be cultured for N. gonorrhoeae and tested for antibiotic susceptibility before a definitive diagnosis is made. Concurrent testing for Ct using nucleic acid tests or culture should be performed.
- Because of the legal implications of a diagnosis of Ct or Ng infection in a child, culture for both organisms remains the preferred method for diagnosis.
3. With the exception of pregnant women, a test-of-cure (i.e., repeat testing 3–4 weeks after completing therapy) is not recommended for persons with documented chlamydia or gonococcal infections who have received treatment with recommended or alterative regimens, unless the patient has persistent symptoms or the clinician suspects therapeutic noncompliance.
- Patients who have symptoms that persist after treatment should be evaluated by culture for N. gonorrhoeae, and any gonococci isolated should be tested for antimicrobial susceptibility.
- Follow up testing for Chlamydia can be performed using the currently available nucleic acid tests.
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