History/Background and/or General Information
Some microorganisms are resistant to certain antimicrobials. Susceptibility testing is often used to determine the likelihood that a particular drug treatment regimen will be effective in eliminating or inhibiting the growth of the infection. A culture of the infected area must be done to obtain the organism for identification and to allow susceptibility testing to be performed if warranted. Referred to by the type of body fluid or cells collected (such as: blood culture, urine culture, sputum culture, wound culture, etc.), the culture involves incubating a sample at body temperature in a nutrient-rich environment. This process promotes the replication of any microorganisms present in the sample. Samples from the skin, stool, or sputum will grow normal flora as well as pathogenic bacteria if they are present. Other body samples, such as blood and urine, are usually sterile; they will show little or no growth unless a pathogenic microorganism is present.
Susceptibility testing is performed by growing the pure bacterial isolate in the presence of varying concentrations of several antimicrobials and then examining the amount of growth to determine which antimicrobials at which concentrations inhibit the growth of the bacteria. Antimicrobial susceptibility testing methods are divided into types based on the principle applied in each system. They include diffusion, dilution, and diffusion & dilution. Results of the testing are reported as “susceptible” (likely, but not guaranteed to inhibit the pathogenic microorganism), “intermediate” (may be effective at a higher than normal concentration), and “resistant” (not effective at inhibiting the growth of the organism). If there is more than one pathogen, the laboratory will report results for each one. The test results should be used to guide antibiotic choice. The results of antimicrobial susceptibility testing should be combined with clinical information and experience when selecting the most appropriate antibiotic for the patient.
Bacterial and fungal cultures are used to define the microbial etiology of the infectious or suspected infectious process and provide a guide for appropriate therapy. Susceptibility studies will be considered medically reasonable and necessary when performed as a result of a positive bacterial culture, and/or less often, positive fungal culture.
Routine screening tests are not payable. Susceptibility studies will not be covered if the culture studies do not identify an organism.
As published in the CMS IOM Publication 100-08, Medicare Program Integrity Manual, Chapter 13, Section 13.5.4, an item or service may be covered by a contractor LCD if it is reasonable and necessary under the Social Security Act Section 1862 (a)(1)(A). Contractors shall determine and describe the circumstances under which the item or service is considered reasonable and necessary.