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Test Name:
Gentamicin, Trough Level
- SBMF No:
29179 - Performance Lab Name:
Automated Lab - Test Mnemonic:
PRE GENT - ABN:
Not required - CPT Code:
80170 - LOINC Code:
3665-7 - Also Known As:
Aminoglycoside
Garamycin® - Also See:
29189 Gentamicin, Peak Level
31009 Gentamicin, Random or Non-Specified - Spec Type:
Serum - Spec Container:
Red top (serum) tube - Alt Spec Type:
Plasma - Alt Spec Container:
Green top (lithium heparin) tube or lavender top (EDTA) tube - Pref Vol:
1.0 mL - Min Vol:
0.3 mL - Fasting:
No - Patient Prep:
Administer IV infusions over 60 minute period
Document exact start and end times of infusions, or exact times of injections, on requisition - Spec Collect:
Do not use gel-barrier tubes for specimen collection
Routine venipuncture
Suggest that drug be dosed using pharmacokinetic procedures
Recommended collection times:
– IV Peak: 30 minutes after end of 1 hour infusion
– IM Peak: 60 minutes after time of injection
– Trough: Immediately prior to start of infusion or just prior to injection - Spec Process:
Within 60 minutes of collection, complete the following:
- Serum sample tubes, clot 30 minutes
- All samples, immediately centrifuge 15 minutes
- Promptly transfer serum or plasma to separate plastic tube
- Ensure that transfer tube label identifies specimen as "peak" and freeze - Spec Store Transport:
Refrigerated - Spec Stability:
1 week refrigerated (2-8°C)
1 month frozen (-20°C) – Do not use frost-free units that undergo repeated freeze/thaw cycles - Spec Remarks:
Some therapeutic drug concentrations are reduced when the sample is stored in a separator tube for a prolonged period of time (greater than 2-6 hours) - Methodology:
Fluorescence Polarization Immunoassay (FPI) - Use:
Used in the diagnosis and treatment of gentamicin overdose and in monitoring levels of gentamicin to ensure proper therapy - Clinical Significance:
Gentamicin is an aminoglycoside antibiotic that exhibits high potency and a broad-spectrum bacterial action against both gram-negative and gram-positive organisms. It exhibits a narrow therapeutic index that makes its use hazardous, especially in patients with impaired renal function. Therefore, accurate monitoring of the serum level in such patients is mandatory. In addition, the dose-serum level profile curve of gentamicin has been found to be surprisingly unpredictable, both in terms of peak-serum levels and elimination half-life from plasma. Strong correlations have been shown between serum levels and both therapeutic effect and toxicity in specific patient types. Peak serum levels of gentamicin in the range of 5 to 10 µg/mL are suggested for optimal therapeutic effectiveness. Persistently elevated peak concentrations have been shown to cause renal and eighth cranial nerve toxicity. Nephrotoxicity takes the form of damage to the proximal renal tubules, and is associated with impaired renal function. Central nervous system toxicity is most often manifested as damage to the vestibular and auditory branches of the eighth cranial nerve. Trough levels offer a more discrete indication of impending toxicity since they more closely correspond to tissue levels and are less affected by sampling errors. Slowly rising trough levels have been shown to correspond to tissue accumulation of the drug, and trough levels greater than 2 µg/mL have been associated with renal failure in some patients. - Reference Range:
Peak: 4-10 µg/mL
Trough: 1-2 µg/mL - Critical High Value:
Peak: >12 µg/mL
Trough: >2 µg/mL - Day Run:
Sun-Sat (daily) - Time Run:
As received - Time Reported:
4 hours - Test Type:
TOX-TDM
