What is the Tobramycin Assay?

The Tobramycin Assay is a blood test used to measure the concentration of tobramycin, an aminoglycoside antibiotic, in the bloodstream. Tobramycin is commonly used to treat serious bacterial infections, particularly those caused by Gram-negative organisms.

Because tobramycin has a narrow therapeutic range, blood levels must be carefully monitored. Levels that are too low may reduce treatment effectiveness, while levels that are too high increase the risk of kidney and hearing damage.

This test is part of therapeutic drug monitoring (TDM) and is typically requested with clinical details such as dosing time, dose amount, and indication.

Why do I need a Tobramycin Assay?

Tobramycin can accumulate in the body, especially in people with reduced kidney function. Monitoring blood levels helps balance effectiveness with safety.

You may need this test if you:

• Are receiving intravenous or inhaled tobramycin
• Are being treated for severe or resistant infections
• Have kidney impairment or fluctuating renal function
• Require dose optimisation during treatment
• Are receiving prolonged antibiotic therapy
• Need monitoring due to age or comorbidities
• Are at risk of antibiotic-related toxicity

Providing clinical details ensures results are interpreted correctly.

Benefits of the test

1. Ensures effective antibiotic dosing
   Confirms therapeutic drug levels are achieved.
2. Reduces toxicity risk
   Helps prevent kidney and hearing damage.
3. Supports dose optimisation
   Enables safe adjustment of treatment.
4. Essential in serious infections
   Used in hospital and specialist care.
5. Accounts for kidney function changes
   Adjusts dosing in renal impairment.
6. Objective therapeutic monitoring
   Provides precise drug concentration data.
7. Improves treatment safety
   Reduces complications from overdosing.
8. Clinically guided interpretation
   Results are tailored using dosing information.

Step-by-step: How we offer testing

Clinic-based testing (UK-wide)

• Choose your nearest UK clinic
• Attend your appointment
• Blood sample taken at a specific time (peak or trough)
• Clinical details recorded (dose, timing, indication)
• Sample sent to the laboratory

Home or hospital-based sampling (+£60 where applicable)

• Mobile phlebotomist arranged when appropriate
• Blood drawn at the correct time relative to dosing
• Sample securely transported to the laboratory

Your results explained

Low level (sub-therapeutic)

• Tobramycin concentration below target range
• UK standards (typical trough): <1 mg/L
• May reduce treatment effectiveness

Therapeutic level

• Tobramycin within target range
• UK standards (typical):
• Peak: 5–10 mg/L
• Trough: <1–2 mg/L
• Suggests appropriate dosing

High level (toxicity risk)

• Tobramycin above recommended range
• UK standards:
• Trough: >2 mg/L
• Increased risk of nephrotoxicity and ototoxicity

Target ranges may vary depending on indication and dosing regimen.