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Gentamicin Trough Level Blood Test

Last updated May 9, 2019

Approved by: Krish Tangella MD, MBA, FCAP

The Gentamicin Trough Level Blood Test is a test to identify the trough levels of gentamicin.

What are the other Names for this Test? (Equivalent Terms)

  • GENTT Blood Test
  • Pregentamicin Trough Level Blood Test

What is Gentamicin Trough Level Blood Test? (Background Information)

  • Gentamicin is an antibiotic that targets bacteria. It is an ‘aminoglycoside’, meaning that it prevents bacteria from making proteins
  • The antibiotic works by binding to the molecular machines in bacteria that make proteins. This prevents the bacteria from growing, but does not necessarily kill them. Thus, gentamicin is a bacteriostatic
  • In contrast, antibiotics that bind to the cell wall, such as vancomicin, rapidly kill bacteria by causing them to swell and burst. The downside to killing is that bacterial components may flood the body and cause a massive immune response, which can be fatal
  • Bacteriostatics, such as gentamicin, do not cause widespread bacterial death, so they may be safer. However, bacteria that are ‘tough and studier’ may simply wait out the bacteriostatic
  • When therapy is stopped, protein production once again resumes and the bacteria can once again cause the disease. This is one of the reasons gentamicin levels need to be carefully monitored and an effective dose maintained at all times
  • Gentamicin levels in blood follow a classic peak and trough pattern. After an individual is administered gentamicin, its levels in blood rise rapidly. They peak 1-2 hours after intake, and then start to drop/fall, until they reach a trough. The trough is the lowest level of gentamicin that the individual will possess
  • The trough usually occurs just before the next gentamicin intake. Peak and trough levels are used to calculate rates of absorption and clearance of gentamicin
  • The Gentamicin Trough Level Blood Test is a test to identify the trough levels of gentamicin. It is used to calculate and determine the necessary amounts of gentamicin to be administered, the timing of the administration, and to ensure that gentamicin levels stay within a safe yet effective range

What are the Clinical Indications for performing the Gentamicin Trough Level Blood Test?

The clinical indications for performing a Gentamicin Trough Level Blood Test include monitoring gentamicin therapy.

How is the Specimen Collected for Gentamicin Trough Level Blood?

Following is the specimen collection process for Gentamicin Trough Level Blood Test:

Sample required: Blood

Process of obtaining blood sample in adults:

  • A band is wrapped around the arm, 3-4 inches above the collection site (superficial vein that lies within the elbow pit)
  • The site is cleaned with 70% alcohol in an outward spiral, away from the zone of needle insertion
  • The needle cap is removed and is held in line with the vein, pulling the skin tight
  • With a small and quick thrust, the vein is penetrated using the needle
  • The required amount of blood sample is collected by pulling the plunger of the syringe out slowly
  • The wrap band is removed, gauze is placed on the collection site, and the needle is removed
  • The blood is immediately transferred into the blood container, which has the appropriate preservative/clot activator/anti-coagulant
  • The syringe and the needle are disposed into the appropriate “sharp container” for safe and hygienic disposal

Preparation required: No special preparation is needed prior to the test.

What is the Significance of the Gentamicin Trough Level Blood Result?

The significance of the Gentamicin Trough Level Blood Test is explained:

  • Excessive gentamicin levels may indicate gentamicin toxicity, which is marked by:
    • Nausea
    • Vomiting    
    • Abdominal pain
  • Low gentamicin levels may indicate that more gentamicin is necessary to achieve a therapeutic dose

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • Antibiotics, such as vancomycin, disrupt the natural bacterial balance in the intestines. This may contribute to digestive side effects and other bacterial infections, such as C. difficile. Probiotics and other therapies may be used to repopulate the gut with healthy bacteria

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider of the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

Please visit our Laboratory Procedures Center for more physician-approved health information:


References and Information Sources used for the Article:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Sept. 7, 2015
Last updated: May 9, 2019