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Lab Manual for UCSF Clinical Laboratories

Lab Manual for SFGH

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Item Value
Available Stat? No (Results available within 2 hours of receipt of specimen in Lab.)
Test code FLUAB
Performed by? Microbiology
Sendout? No
Price range $$$
In House Availability 24 hours daily. (See Additional Information below.) Turn-around-time: approximately 2 hours from receipt of specimen in lab.
Principle The Cepheid Xpert Flu Assay, performed on the Cepheid GeneXpert Dx System, is an automated qualitative in vitro diagnostic test for rapid detection of influenza A and influenza B viral RNA.

The GeneXpert Dx System automates and integrates sample purification, nucleic acid amplification, and detection fo the target sequence in samples using real-time PCR and RT-PCR assays. The system utilizes single-use, disposable cartridges that hold PCR reagents and host the PCR process.

The Xpert Flu Assay includes reagents for the detection and differentiation of influenza A and influenza B directly from nasal or nasopharyngeal wash/aspirate and nasal/nasopharyngeal swab specimens of patients with signs and symptoms of respiratory infection.
Interpretation INTERPRETATION: This rapid test is only a screening test. A negative test may indicate the absence of influenza A and/or B or may be a false negative result due to improper specimen collection (especially absence of appropriate cellular material), improper specimen handling, or virus amounts lower than detectable levels. A positive test suggests the presence of influenza A or influenza B antigen. However, some specimens may give false positive results. The predictive value of a positive result decreases at the beginning and end of the influenza season when the prevalence of influenza is low.

Reported sensitivities and specificities1 with nasal or nasopharyngeal wash/aspirate (nasopharyngeal swab):

Sensitivity Specificity
Influenza A 85.7% (100%) 99.1% (98.3%)
Influenza B 100% (87.5%) 99.4% (99.7%)

CLINICAL SIGNIFICANCE: Results must be interpreted in conjunction with clinical findings and other laboratory data. If there is any question about a rapid test result, it is recommended that viral culture be ordered.
Container type 1. Put nasopharyngeal wash/aspirate specimens in sterile, leak proof containers (viral transport medium collection tubes are preferred).

2. For NP swab specimen, use swabs provided with viral transport medium (obtained from Lab Support Services, 206-8199) for collecting specimens. If viral transport packages are not available, dacron swabs may be used and placed into a small amount (approx. 0.5 ml) of sterile non-bacteriostatic saline in a sterile tube. DO NOT USE CALCIUM ALGINATE SWABS.
Collection Instructions Wash/aspirate: Have patient recline at 45 degrees so that saline introduced does not directly flow out. Introduce a few drops to 1 mL of sterile saline (from a pink respiratory therapy ampule) into anterior nares. Insert an appropriate sized catheter (usually about #6 or #8 French) into the nose to the distance between the nares and the ear or until resistance is encountered. Suction intermittently through a mucus or DeLee specimen trap. Remove catheter and flush the line with no more than 2 mL of saline. Use of larger volumes will dilute the specimen and diminish the sensitivity of the test. Seal collection container.

Nasopharyngeal swab: Insert thin mini-tip swab through a nostril and into the posterior nasopharnyx and rotate the swab several times to collect mucosal epithelium. After collecting specimen, aseptically break swab into tube of transport medium and cap tightly.

NOTE: The large tip swab that is included in the package with the viral transport media can be used initially to clean mucus out of the nose. Then discard this large swab and collect specimens with thin mini-tip swap in package.
Sample type Nasal/nasopharyngeal wash or aspirate; nasopharyngeal swab.
Special instructions REQUISITION: Microbiology (Viral - Rapid test for influenza A and B)

Deliver to the Microbiology laboratory (2M33) immediately after collection or refrigerate until delivery.
Normal range NEGATIVE. Influenza A and influenza B target RNA not detected.
Synonyms Nasopharyngeal Aspirate, Viral Detection From;
Stability 24 hours at 4-8°C
Additional information NOTE: If avian influenza is suspected at any time, immediately contact Infection Control (pager: 415- 443-1566) and the Microbiology Lab Medicine Resident (pager: 415-443-1438) Monday through Friday from 8:00 a.m. to 5:00 p.m. After hours and weekends, call the Clinical Laboratory Information Section (Inquiry) at 415-206-8590, and request their assistance to contact the Chief of Microbiology.

For safety reasons, only rapid molecular testing will be done if avian influenza is suspected. Cultures will not be done. Specimens may be sent to the Department of Public Health for further testing.

References 1. Product Insert. Xpert FLU Assay. Cepheid. Sunnyvale, CA. 300-9683 Rev. A, May 2011.

2. Miller, S., Moayeri, M., Wright, C., Castro, L. and Pandori, M. (2010) Comparision of GeneXpert Flu A PCR to Direct Fluorescent Antibody and Respiratory Viral Panel PCR Assays for Detection of 2009 Novel H1N1 Influenza Virus. JCM 48(12): 4684-5.

Last Updated 7/2/2018 3:46:12 PM
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