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Antibiotic (cephalexin) concentration in plasma or serum

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of the antibiotic cephalexin in your blood. It helps doctors determine if your dose is working effectively and adjusts treatment as needed.

Quick summary

["This test helps ensure your cephalexin antibiotic is at the right level to fight infection safely."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
73459-0
Short code
Cephalexin ind plt IgM SerPl Ql FC
Synonyms
Cephalexin ind plt IgM SerPl Ql FC
Category
hematology
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
flow-cytometry
CPT
82784
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Is Done

Your doctor may order this test if you’re taking cephalexin to treat or prevent bacterial infections. It helps monitor whether the antibiotic is reaching the right amount in your bloodstream to clear the infection without causing side effects.

What to Expect Before the Test

No special preparation is needed. You’ll provide a blood sample, usually drawn from your arm. The sample is taken to a lab for testing.

What the Test Results Mean

Results help your doctor check if your cephalexin levels are therapeutic (effective but not harmful). Low levels may mean the infection isn’t fully treated, while high levels could signal toxicity.

Common Uses and Considerations

This test is often used in patients with kidney issues or those taking multiple medications, as cephalexin is processed by the kidneys. It may also be used in monitoring long-term therapy.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Antibiotic levels like cephalexin are critical for balancing effectiveness and safety. Therapeutic drug monitoring ensures the drug reaches optimal concentrations to kill bacteria while minimizing risks like kidney damage or allergic reactions.

Short name

Cephalexin Level

Frequently asked questions

Will I feel any pain or discomfort during the blood draw?
You may feel a slight pinch or sting when the needle is inserted, but it usually goes away quickly. Most people describe it as mild discomfort.
How long will it take to get my results back?
Results are typically available within 1–3 business days, depending on lab processing times. Your doctor will contact you with the final report.
Can I eat or drink before this test?
You can eat and drink normally before the test, as no fasting is required. However, always follow your doctor’s specific instructions for your situation.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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 16, 2026. · Read our editorial policy