Isothermal Molecular C. Diff Tests Ideal for Small, Mid-Sized Labs

Two molecular in vitro diagnostic assays that utilize isothermal reactions to detect toxigenic C. difficile are accurate, yet “fast” and “relatively simple to use” compared to most of the PCR-based assays, according to a study published in the August issue of Diagnostic Microbiology and Infectious Disease. The data shows that AmpliVue (Quidel) and Illumigene (Meridian Biosciences) can be used in diverse laboratory settings with both adult and pediatric patient populations.

Reliable and quick detection of the presence (or absence) of C. diff toxin genes in stool samples, can result in faster initiation of the proper treatment of patients and initiation of infection control measures to prevent the spread of the disease, especially in health care environments. While there has been growing interest in the sensitivity of molecular assays for the diagnosis of C. diff infections, most of the early U.S. Food and Drug Administration-cleared nucleic acid amplification tests require extraction of genomic material on a separate instrument followed by amplification using thermocyclers. While these are an improvement over the gold standard diagnostic method of cytoxigenic culture, diagnostics involving isothermal reactions may achieve similar performance in a relatively simple test format, compared to polymerase chain reaction- (PCR-) based assays.

In the current DMID study, laboratorians at multiple sites (two children’s hospitals [median age less than 10 years] and one general hospital [median age 58 years]) evaluated the use of isothermal amplification chemistries for detection of C. diff using fresh specimens. These assays were used in hospital laboratories with low- to medium-volume C. difficile testing (January 2013 to September 2013). All 758 stool samples were tested for the presence of C. diff toxin gene using the Illumigene assay (isothermal loop-mediated isothermal amplification) as the test of record. Remnant stool specimens that were enrolled in the study were deidentified and tested with the AmpliVue assay (isothermal helicase-dependent amplification). Any discordant results were resolved by performing toxigenic culture.

The researchers found that the two assays showed 97.8 percent concordance overall. Following discordant resolution, the combined performance for all three sites for the AmpliVue assay and Illumigene assays were: 96.1 percent sensitivity for both; 99.2 percent and 99.8 percent specificity, respectively; 96.1 percent and 99.2 percent positive predictive value, respectively; and 99.2 percent negative predictive value for both. This study found that in patients less than two years of age the assays performed similarly, suggesting that these kits can be reliably used in this population.

The methods studied here offer several advantages,” writes lead author Stella Antonara from Nationwide Children’s Hospital (Columbus, Ohio). “They do not require specialized training of technologists, they can be performed on demand without having to batch samples, and the results can be available within hours of receipt of the sample. These assays are ideal for small- to medium-sized laboratories that lack room and capabilities for larger PCR systems due to their small space requirements.”

Takeaway: Metabolomic profiles in serum may be useful in screening women for early- stage ovarian cancer. While further validation in larger populations is necessary, the researchers say a clinical assay based on the 16 markers is technically feasible.