Mycobacterium tuberculosis and Rifampin Resistance by PCR, Fairview Range Medical Center only


Sunquest Code:MTBPCR  
Epic Code:LAB6789Epic Name:MTB Rif by PCR (Range)
Synonyms:MTBPCR
Methodology:Polymerase chain reaction (PCR)
CPT Code:87556
Turnaround Time:Performed daily; results are reported within 24 hours.


Collection Instructions

Specimen:Sputum
Optimal Volume:1 mL
Minimum\Peds Volume:0.5 mL
Collection Instructions:Recommend early morning sputum collection., If a second MTB-RIF test is required; a specimen collected 8 hours after the first collection is preferred. See the reference range for sensitivity and negative predictive values for 1 and 2 tests.
Causes for Rejection:Samples with obvious food particles or other solid particulate.
Contraindications:The Xpert MTB/RIF assay is not indicated for use with sputum samples from patients being treated with antituberculosis drugs either to determine bacteriologic cure or to monitor response to therapy. Assay interference may be observed in the present of Lidocaine (>20% v/v), mucin (>1.5% w/v), Ethambutol (>5 ug/mL), Guaifenesin (>2.5 mg/mL), Phenylephrine (25% v/v), or tea tree oil (>0.008% v/v) The performance of the Xpert MTB/RIF assay has not been evaluated with samples from pediatric patients.


Processing and Shipping

Specimen Processing:Do not process. Send immediately to laboratory.
Shipping Instructions:Send immediately to laboratory.
Test Performed at or Referral Lab Infectious Diseases Diagnostic Laboratory-Virology  (Fairview Range - FRMC)


Interpretive

Reference Range:Xpert MTB-RIF and AFB stain sensitivity and Negative Predictive Value (NPV) as compared to culture: One Xpert vs. culture: 85.2% sensitive, NPV=99.7% Two Xpert ordered 8-24 hours apart vs. culture: 91.2% sensitive, NPV=100% 2 AFB stain vs. culture: 69.2% sensitive A reference range has not been established for pediatric patients.
Use:This test is FDA approved only for assessing isolation requirements for patients who are admitted to or potentially admitted to airborne precautions (negative air pressure). This test is NOT diagnostic for MTB. Cultures must also be ordered according to possible Mycobacterium tuberculosis protocols. Rifampicin (rpoB gene) resistance by PCR will be reflexed for positive tests for MTB. These results may guide treatment; however, culture with susceptibility testing is required to confirm the rifampicin results. A negative rifampicin resistance screen by Xpert MTB-RIF indicates likely susceptibility but NOT definitive susceptibility. Further testing is required.


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