The Test Sample
What is being tested?
Vancomycin is an antimicrobial drug that is used to treat serious infections caused by Gram-positive bacteria. Developed in the 1950s, vancomycin was originally prescribed primarily when organisms proved resistant to penicillin or when a person was allergic to penicillin. Its use declined with the introduction of other antimicrobials such as methicillin but has risen again with the emergence of certain strains of Staphylococcus, such as methicillin-resistant Staphylococcus aureus (MRSA). This test measures the concentration of vancomycin in the blood.
It is important to monitor the level of vancomycin because its effectiveness depends on sustaining blood levels at a minimum concentration for the duration of therapy. Furthermore, excessive concentrations of vancomycin must be avoided because high levels can result in serious side effects, specifically damage to hearing (ototoxicity) and kidney damage (nephrotoxicity). The amount of vancomycin given per dose depends on a variety of factors, including kidney function, other nephrotoxic drugs the person may be taking, age, and weight.
Decreased kidney function may prevent efficient clearance of vancomycin from a person's system, resulting in increased concentration in the blood. If a person is given too little drug and is unable to maintain a sufficient minimum dose in the blood, then it is unlikely that treatment will be effective. The vancomycin test can be used to monitor the amount of drug in the blood to ensure that it remains at a therapeutic concentration – that is, adequate but not excessive.
Vancomycin is given intravenously (by injection into a vein) to treat infections such as septicemia, endocarditis, infection of the bone (osteomyelitis), some pneumonias, and meningitis. It is often the drug of choice for methicillin-resistant Staphylococcus epidermidis and MRSA infections, especially when they are associated with implanted prosthetic devices such as heart valves, artificial hips, and indwelling catheters. Vancomycin may also be given to some people before specific surgeries and dental procedures to prevent an infection. Intravenous vancomycin administration is necessary to get the drug into circulation because oral vancomycin is poorly absorbed. Oral vancomycin is prescribed to treat some resistant Clostridium difficile infections. These occur in the gastrointestinal tract, where absorption into the circulating blood is not needed. Vancomycin is also used for patients who are intolerant or allergic to beta-lactams.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed, but the timing of the sample for testing is important. Follow instructions provided for collection and tell the laboratorian when the administration of the last intravenous dose was completed.