Diagnostic ambiguity in C. difficile

Sept. 21, 2017

Clostridium difficile (commonly referred to as C. diff), a bacterium found in air, water, soil, and feces, is one of the potentially hundreds of thousands of different bacteria that can and do live in harmony with one another in the intestines of healthy individuals. However, the normal intestinal balance can become disrupted, most commonly through a combination of illness and antibiotic use, creating an environment where some of the “good” bacteria are eliminated and the body’s immune system is compromised and vulnerable. The medication-associated risk factors for developing C. difficile include:

  • Currently taking or having recently taken antibiotics
  • Taking broad-spectrum antibiotics that target a wide range of bacteria
  • Using multiple antibiotics
  • Taking antibiotics for a long time
  • Taking medications to reduce stomach acid, including proton pump inhibitors.1

In such situations, C. difficile can take over, colonize, and begin producing toxins that can result in C. difficile infection (CDI). CDI has become the most common cause of healthcare-associated infections in U.S. hospitals and is the leading cause of gastroenteritis-associated death. Symptoms include diarrhea more than three times a day, severe cramping, fever, nausea, and dehydration. According to a study funded by the Centers for Disease Control and Prevention (CDC), C. difficile was responsible for almost 500,000 infections and was associated with approximately 29,000 deaths in 2011. Additional reports suggest that these numbers have continued to rise in subsequent years. Healthcare costs related to C. difficile infection are estimated at $4.8 billion for acute care facilities alone.2

Antibiotics and testing methods

Given this background on the increasing challenge that CDI represents to both individuals and to the healthcare system, the importance of rapid and effective diagnosis and treatment is evident. Accurate diagnosis is important because administering antibiotics to someone with CDI is helpful, but administering the same antibiotics to someone who does not have CDI can lead to increased susceptibility to infection. False negatives or false positives are not only bad for the individual patient, but they also lead to wasted resources in terms of money and time (treating those who do not have the disease or not treating people who do have it quickly enough and then bearing the cost when the disease spreads).

Unfortunately, the two types of tests currently available for diagnosing C. difficile are both lacking in different ways.

With regard to molecular testing, nucleic acid amplification tests (NAATs) and polymerase chain reaction (PCR) can identify with high sensitivity whether or not C. difficile is present in a person’s stool, but not whether the organisms are producing the disease-causing toxins. Molecular tests therefore often lead to false positive results.

With regard to immunoassays, these tests are capable of detecting the toxins that cause disease and are therefore much more specific to CDI than molecular tests; however, currently available immunoassays lack sensitivity and often lead to false negative results. To compensate for this inadequacy, an additional immunoassay test that detects glutamate dehydrogenase (GDH), a biomarker produced by members of the Clostridium family, is combined with the toxin testing to increase the clinical sensitivity.

The costs of ambiguity

Consider a patient who has CDI and receives an immunoassay test that is not sufficiently sensitive. The patient may be highly contagious to healthcare workers and to other patients, but the lack of sensitivity of the immunoassay test can result in a false negative. If this happens, the infectious person is not isolated and treated right away, increasing the likelihood that the disease will spread to others. This adds cost to the hospital, which must now treat the initial patient, test and treat subsequent patients, undergo decontamination once the untreated disease spreads, and so on.

On the other hand, what if a patient has the C. difficile organism present but does not have CDI (meaning the toxins are not present)? If this patient gets tested with a molecular method, the test will come back as a false positive. The hospital will follow protocol for a CDI patient, isolating immediately and undergoing an extensive, costly cleaning regimen to prevent the spread of what they think is disease. The wasted cost here is associated with unnecessary treatment and quarantine measures.

The cost of treating—or not treating—patients based on tests that are inaccurate can be high for clinicians and hospitals. Because clinicians know about the limitations of each test type, often times hospitals decide to test for C. difficile using both the molecular and immunoassay methods. Insurance companies will not reimburse for several different types of testing, but often the hospital decides to take on that extra cost itself, understanding that doing so will cost less in the long run than the cost associated with the false positives and false negatives these tests can yield. Clinicians, laboratorians, and healthcare administrators often express the need for a more sensitive toxin immunoassay test, because the detection of toxins is better correlated with presence of CDI.

The big picture

With factors like antibiotic use, previous diagnosis, and insufficient testing methods, making an accurate CDI diagnosis is not a simple task. In fact, physicians often have different testing methods and standard procedures for arriving at a CDI diagnosis, because no one method is definitive. What we need as an industry is a single, cost-effective, rapid immunoassay with greater sensitivity. Only then can we move the diagnosis of C. difficile from a complex puzzle that requires multiple pieces of information to a straightforward process that leads to confident treatment decisions, while dramatically bringing down both the cost and incidence of CDI disease.


  1. Mayo Clinic. C. difficile Infection, Symptoms and Causes. http://www.mayoclinic.org/diseases-conditions/c-difficile/symptoms-causes/dxc-20202389.
  2. Lessa FC, Mu Y, Bamberg WM, et al. Burden of Clostridium difficile infection in the United States. N Engl J Med. 2015;372(9):825-834.

Jeff Bishop, PhD, RAC, serves as Senior Vice President of Research and Development at immunodiagnostics company Singulex, Inc. He has worked in the diagnostics industry for more than 17 years, and has extensive experience working with biomarkers. He has led the development of many drug and biomarker assays on numerous platforms across a wide range of disease states.