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Test Code LAB38 Tobramycin Level, Trough, Blood

Performing Laboratory

St. Louis Children's Hospital - Chemistry

Specimen Requirements

Patient Preparation: None

Container/Tube  
Preferred: Mint green-top Lithium Heparin (MNTGRN LiHep) tube
Acceptable: Green samplette/microtainer, plain red-top tube, Lavender-top (EDTA) tube, or Gold SST gel tube

Collection Volume: 1.0 mL (minimum 0.6 mL)

Submission Container/Tube: If specimen is coming from outside facility and collected in a microtainer, Lavender-top (EDTA) tube, or plain red-top tube aliquot processed sample into a plastic vial for transport (labeling with specimen type).
Special Instructions: Specimen should be collected 30 minutes prior to next dose.

Sample Rejection

Mislabeled or unlabeled specimens

Logistics

Test Availability: Monday-Sunday
Cut-off time: None; performed as received
Turnaround Time: Same day; 2 hours from receipt in performing lab

Reference Values

Therapeutic Range: 

< 18 years: <1.0 mcg/mL
≥ 18 years: ≤ 2.0 mcg/mL                                                          

Critical Values: >2.0 mcg/mL

Critical test results will be automatically called back initially and every 24 hours thereafter.

Methodology

Enzyme Immunoassay 

Limitations

  • Amikacin cross-reacts with this assay. Kanamycin cross-reacts significantly; however, the assay has not been optimized to quantitate this aminoglycoside. Aminoglycosides are not generally coadministered in clinical practice, although more than one aminoglycoside may be present when switching from treatment with one to another. Samples that contain tobramycin in combination with either Amikacin or Kanamycin cannot e reliably quantitated by this assay.
  • In very rare cases, gammopathy, in particular type IgM (Waldenstrom's macroglobulinemia), may cause unreliable results.

 

Additional Information

FOR SLCH CORE LABORATORY USE ONLY

Lab Processing Instructions: Centrifuge specimen to separate. If specimen is collected in a plain red-top tube, microtainer, or Lavender-top (EDTA) tube aliquot sample into a Roche false-bottom tube for testing (labeling with specimen type).
Processed Volume: 0.3 mL plasma/serum
Analyte Stability:

Specimen Type Temperature Time  
Whole Blood (unprocessed)  Ambient 8 hours  
Plasma/Serum (processed) Refrigerated (preferred) 2 days  
  Ambient  8 hours  
  Frozen  1 month        
Note: specimen should not be repeatedly frozen and thawed  

LOINC

in process

Last Reviewed

06/2025

Test Classification and CPT Coding

80200