- No FAQs found
- ABL Kinase Domain Mutation in CML, Cell-based
- ABO Group and Rh Type
- Acid-Fast Bacillus (AFB) Identification, Sequencing and Stain, Paraffin Block
- ADAMTS13 Activity with Reflex to ADAMTS13 Inhibitor
- Alcohol Metabolites, Quantitative, Urine
- Alpha-Globin Common Mutation Analysis
- Alpha-Globin Gene Deletion or Duplication
- Alpha-Globin Gene Sequencing
- Anti-Müllerian Hormone AssessR™
- Anti-PF4 and Serotonin Release Assay (SRA) for Diagnosing Heparin-induced Thrombocytopenia/Thrombosis (HIT/HITT)
- Antiphospholipid Antibodies
- ASCVD Risk Panel with Score
- Autoimmune Epilepsy Evaluation
- Autoimmune Diseases, Tests for
- B-cell and T-cell Clonality Assays by PCR
- B-Type Natriuretic Peptide (BNP)
- BCR-ABL1 Gene Rearrangement, Quantitative PCR
- Beta-Globin Complete
- BRCAvantage®, Ashkenazi Jewish Screen
- BRCAvantage®, Rearrangements
- BRCAvantage™, Comprehensive
- BRCAvantage™, Single Site
- CDH1 Sequencing and Deletion/Duplication
- Clostridium difficile Diagnostic Testing
- C1 Inhibitor, Protein and Functional Tests
- Calreticulin (CALR) Mutation Analysis
- Carbapenem Resistant Enterobacteriaceae Culture Screen
- Cardio IQ Lipoprotein Fractionation, Ion Mobility
- Cervical Cancer, TERC, FISH
- CFvantage® Cystic Fibrosis Expanded Screen
- Chlamydia trachomatis, TMA
- Chlamydia trachomatis/Neisseria gonorrhoeae RNA, TMA
- Chromosomal Microarray, POC, ClariSure®, Oligo-SNP
- Chromosomal Microarray, Postnatal, ClariSure® Oligo-SNP
- Chromosome Analysis and AFP with Reflex to AChE, Fetal Hgb, Amniotic Fluid
- Chromosome Analysis, Amniotic Fluid
- Chromosome Analysis, Blood
- Chromosome Analysis, Blood with Reflex to Postnatal, ClariSure® Oligo-SNP Array
- Chromosome Analysis, Chorionic Villus Sample
- Chromosome Analysis, High Resolution
- Chromosome Analysis, High Resolution with Reflex to Postnatal, ClariSure® Oligo-SNP Array
- Chromosome Analysis, Mosaicism
- Chromosome Analysis, Neonatal Blood
- Chromosome Analysis, Sister Chromatid Exchange
- Chromosome Analysis, Tissue
- Chromosome DEB Assay for Fanconi anemia
- Chronic Lymphocytic Leukemia (CLL) - Diagnostic and Prognostic Testing
- Culture, Fungus
- Culture, Urine, Routine
- Cystic Fibrosis Screen
- Cytomegalovirus (CMV) and Epstein Barr Virus (EBV) PCR
- D-Dimer, Quantitative
- Dementia, Secondary Causes
- Dengue Virus Testing
- Diabetes Risk Panel with Score and Cardio IQ® Diabetes Risk Panel with Score
- Drug Testing, General Toxicology (Blood, Urine, or Serum)
- Drug Toxicology Alcohol Metab, QN, Oral Fluid
- Drug Toxicology Monitoring, Oral Fluid Testing
- Factor V (Leiden) Mutation Analysis
- Familial Mediterranean Fever Mutation Analysis
- First Trimester Screen, hCG
- First Trimester Screen, Hyperglycosylated hCG (h-hCG)
- FISH, Angelman
- FISH, MET Amplification
- FISH, Myeloma, 17p-, rea 14q32 with Reflexes
- FISH, Prader-Willi
- FISH, Prenatal Screen
- No FAQs found
- HCV Genotyping
- Helicobacter pylori (H pylori) Antibody Discontinuation
- Heparin, Anti-Xa
- Hepatitis B Surface Antibody, Quantitative
- Hepatitis B Surface Antigen, Quantitative, Monitoring
- Hepatitis C Antibody with Reflex to HCV RNA, PCR with Reflex to Genotype
- Hepatitis C Viral RNA Genotype 1 NS5A Drug-resistance
- Hepatitis C Viral RNA Genotype 3 NS5A Drug Resistance
- Hepatitis C Viral RNA NS3 Drug Resistance
- Hepatitis C, RNA, Quantitative, PCR
- Hereditary Cancer Panels: MYvantageTM Hereditary Comprehensive Cancer Panel and GIvantageTM Hereditary Colorectal Cancer Panel
- Hereditary Hemochromatosis DNA Mutation Analysis
- Herpes Simplex Virus (HSV) Type-Specific IgG Antibodies
- Herpes Simplex Virus Type 2 (HSV-2) IgG Inhibition, ELISA
- HIV-1 Coreceptor Tropism, Proviral DNA
- HIV-1 Coreceptor Tropism, Ultradeep Sequencing
- HIV-1 Integrase Genotype
- HIV-1/2 Antigen and Antibodies, Fourth Generation, with Reflexes
- HPV mRNA E6/E7
- Influenza A and B Antigen, Immunoassay
- Influenza Type A and B Antibodies
- Insulin, Intact, LC/MS/MS
- Integrated Screen, Part 1
- Integrated Screen, Part 2
- Intrinsic Factor Blocking Antibody
- No FAQs found
- No FAQs found
- Maternal Serum AFP
- Melanoma, BRAF V600E and V600K Mutation Analysis, THxID®
- Metanephrines, Fractionated, Free, LC/MS/MS, Plasma
- Methylenetetrahydrofolate Reductase (MTHFR), DNA Analysis
- Microalbumin (Urinary Albumin Excretion)
- Pain Management and CYP2D6/CYP2C19
- Pain Management, Naltrexone, Quantitative, Urine
- Partial Thromboplastin Time, Activated (aPTT)
- Penta Screen
- PIK3CA Mutation Analysis
- Platelet Antibody Screen (Indirect)
- PNH with FLAER (High Sensitivity)
- Prothrombin Time with INR
- PTH, Intact and Calcium
- Streptococcus pneumoniae (Pneumococcal) Antibody Tests
- Saccharomyces cerevisiae Antibodies (ASCA) (IgG, IgA)
- Sequential Integrated Screen, Part 1
- Sequential Integrated Screen, Part 2
- Serum Integrated Screen, Part 1
- Serum Integrated Screen, Part 2
- Serum Pregnancy Tests
- Sickle Cell Screen
- Stepwise, Part 1
- Stepwise, Part 2
- SureSwab® Trichomonas vaginalis RNA, Qualitative TMA
- SureSwab®, Candidiasis, PCR
- TP53 Sequencing and Deletion/Duplication
- T4, Free
- Tamoxifen and Metabolites, LC-MS/MS
- Testosterone Testing
- Total Testosterone, LC/MS/MS
- Triple Screen
- No FAQs found
- No FAQs found
- No FAQs found
Clostridium difficile Toxin/Glutamate Dehydrogenase (GDH) with Reflex to PCRTest code(s) 91664
This is an outdated version of this FAQ. It was effective 03/24/2015 to 03/03/2017.
The current version is available here.
Question 1. What is the significance of C difficile in the healthcare setting?
C difficile is an opportunistic, toxin-producing bacterial pathogen of the gastrointestinal tract that is the most common cause of healthcare-associated diarrhea. It causes 25% to 30% of antibiotic-associated diarrhea and >95% of pseudomembranous colitis cases. Incidence has almost doubled since 1996, and the mortality rate is rising owing to emergence of a hypervirulent strain (ribotype 027/NAP1/toxinotype III).
Disease-causing C difficile strains produce 1 or both of 2 toxins: toxin A is an enterotoxin and toxin B is a cytotoxin. Other strains produce neither toxin and are thought to be avirulent.
Question 2. What is the new test being introduced for C difficile testing?
This new test is a rapid, membrane enzyme immunoassay that simultaneously detects C difficile glutamate dehydrogenase (GDH) antigen and toxins A and B in a single reaction well. It is a manual cartridge-based test that requires no instrumentation. GDH antigen is a metabolic enzyme expressed at high levels by all strains of C difficile and some other Clostridium species.
Question 3. What is the reason for introducing this new test?
Studies have shown that EIA testing for C difficile toxins A and B lacks diagnostic sensitivity; some studies show sensitivity as low as 31%. For diagnosis of C difficile infection, it is recommended to use either 1) nucleic acid amplification testing (NAAT) or 2) a combination of GDH antigen and toxin detection with NAAT confirmation of discordant results. The C difficile toxin A and B EIA assay has been discontinued by Quest Diagnostics due to its relatively low sensitivity.
Question 4. Are there any changes to specimen collection requirements?
Specimen collection and transport instructions remain the same as the previous C difficile EIA toxin A/B test with one exception: formed stools are no longer accepted for the new GDH/toxin test.
Question 5. How will the reflex testing work?
If both the toxin A and B test and the GDH test are positive, then the sample will be considered positive for toxigenic
C difficile infection. If both the toxin and GDH tests are negative, then the sample will be considered negative for toxigenic
C difficile infection (Figure). Samples with discordant results (ie, GDH-positive but toxin-negative or GDH-negative but toxin-positive) will be reflexed (at additional charge and additional CPT code) for confirmation with C difficile PCR. The C difficile PCR test targets the toxin B gene (tcdB). According to our validation studies, the above discordant results may occur about 6% of the time.
Question 7. Should we test neonates using this assay?
Up to 50% of neonates may be colonized with toxigenic C difficile. While testing for C difficile in this population will be performed, results should be interpreted with caution.
Question 8. How are C difficile infections treated?
For decades, the drugs of choice were either vancomycin or metronidazole. However, the recurrence rate associated with these antibiotics is 20% to 30%, which is unacceptability high. Fidaxomicin is an alternative that has a lower relapse rate than vancomycin. There is no strong evidence that probiotics aid in the treatment of C difficile disease.
- American Society for Microbiology. A practical guidance document for the laboratory detection of toxigenic Clostridium difficile. 2010. http://www.alere.com/content/dam/alere/docs/guidelines/2010_ASM_guidelines_dated_9.21.10.pdf. Accessed February 10, 2014.
- Cohen, SH, Gerding DG, Johnson, SN, et al. 2010. Clinical practice guidelines for Clostridium difficile infection in adults: 2010 Update by the Society for Healthcare Epidemiology of America (SHEA) and the Infectious Diseases Society of America (IDSA). Infect Control Hosp Epidemiol. 2010;31(5):431-455.
- Cornely OA, Miller MA, Louie TJ, et al. Treatment of first recurrence of Clostridium difficile infection: fidaxomicin versus vancomycin. Clin Infect Dis. 2012;55(suppl 2):S154-S160.
- Swindells J, Brenwald N, Reading N, et al. Evaluation of diagnostic tests for Clostridium difficile infection. J Clin Microbiol. 2010;48:606-608.
- Surawicz CM, Brandt LJ, Binion DG, et al. Guidelines for diagnosis, treatment, and prevention of Clostridium difficile infections. Am J Gastroenterol. 2013;108:478–498.
- Versalovic J, Carroll KC, Funke G, et al. Manual of Clinical Microbiology. 10th ed. Washington D.C: ASM Press; 2011.