Free Cefazolin Concentration (Serum/Plasma)
This test measures the amount of free (unbound) cefazolin, a type of antibiotic, in your blood. It helps doctors assess how much of the drug is actually available to fight infection.
["Understanding your free cefazolin levels helps tailor antibiotic dosing for better infection control."]
Key facts at a glance
- LOINC
- 80962-4
- Short code
- CEFAZFR
- Synonyms
- ceFAZolin free SerPl-mCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top serum tube (no anticoagulant) or serum separator tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
- CPT
- 80299 (Quantitation of therapeutic drug, not otherwise specified)
- SNOMED
- 419943002
- Specimen volume
- 1-2 mL serum
- Stability
- Serum should be frozen at -20°C or lower if not analyzed within 24 hours. Stable for up to 30 days when stored at -20°C.
- Hemolysis max
- 100
- Lipemia max
- 100
- Icterus max
- 50
- TAT
- 24–72 hours
- Order
- routine
Why This Test Is Done
Your healthcare provider may order this test if you’re receiving cefazolin treatment to monitor its effectiveness. Free cefazolin levels are particularly important because they reflect the drug’s true biological activity against bacteria. This can help prevent excessive dosing (which may cause side effects) or insufficient dosing (which may fail to treat infection).
What to Expect Before the Test
No special preparation is needed. You’ll have a small needle inserted into a vein (usually in your arm) to draw blood. The process is quick and typically painless. If you’re on blood thinners or have a history of bleeding issues, let your doctor know beforehand.
What the Results Mean
Results are compared to your specific dosing regimen and clinical situation. Higher-than-expected levels may indicate the drug isn’t clearing properly, while lower levels might suggest the infection isn’t responding. Your doctor will discuss these findings in the context of your treatment plan.
Common Causes of Abnormal Results
Abnormal results could be due to kidney function issues (which affect drug clearance), improper dosing, or certain medications that interact with cefazolin. Rarely, it may reflect liver problems or changes in how your body absorbs the drug.
Reference range
Therapeutic ranges are interpreted in the context of the minimum inhibitory concentration (MIC) of the infecting organism and the site of infection. Target free drug concentrations should typically exceed the MIC for the dosing interval.N/A
No special preparation required. Trough levels are typically drawn immediately before the next scheduled dose. Peak levels (if ordered) are drawn 30-60 minutes after the end of infusion for renally cleared agents.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Short name
Free Cefazolin Level
Frequently asked questions
How often should I get this test?
What if my levels are too high?
Can I drink alcohol before this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 15, 2026. · Read our editorial policy