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Serum Concentration of Ceftriaxone (Parentally Administered)

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

This test measures the amount of the antibiotic ceftriaxone in your blood serum after it has been given through an intravenous (IV) line. Ceftriaxone is often used to treat serious bacterial infections.

Quick summary

["Your doctor may check this level to ensure the antibiotic is working properly and at the right dose for your condition."]

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

Key facts at a glance

LOINC
18896-1
Short code
CEFPAR
Synonyms
Cefuroxime Parenter Susc Islt
Category
chemistry
Sample
serum
Container
Sterile transport container or culturette swab transport system; serum separator tube (SST) for serum samples
Units
N/A
Ref low
8
Ref high
16
Fasting
false
Population
adult
Sex
all
Age range
≥ 0 years
Method
Broth microdilution (MIC determination)
CPT
87186
SNOMED
103138008
Specimen volume
2-5 mL of serum or sufficient isolate/pure culture for susceptibility testing
Stability
Serum: 24 hours at room temperature, 48 hours at 2-8°C; Culture isolate: stable for 24-48 hours on appropriate media at room temperature
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
24–72 hours
Order
routine

Why Is This Test Done?

Your healthcare provider may order this test if you’re receiving ceftriaxone treatment for an infection, such as sepsis, meningitis, or pneumonia. It helps monitor how well the drug is reaching your bloodstream and whether it’s effective against the bacteria causing your illness.

What Does This Test Tell You?

The result helps doctors adjust your treatment plan. For example, if levels are too low, they may increase your dose. If levels are too high, they may change your treatment or monitor you more closely for side effects.

How Is the Sample Collected?

A blood sample is taken from a vein, usually in your arm. You may feel a small pinch when the needle is inserted, but the procedure is quick and typically doesn’t cause long-lasting discomfort.

What Should You Expect Before or After the Test?

No special preparation is needed. If you’re on other medications or have certain health conditions, let your doctor know before the test. After the blood is drawn, you can resume normal activities, though you may experience mild bruising or soreness at the site.

Reference range

Susceptible: ≤4 mcg/mL (zone ≥23 mm); Intermediate: 8-16 mcg/mL (zone 15-22 mm); Resistant: ≥32 mcg/mL (zone ≤14 mm). Interpretive criteria per CLSI M100 guidelines.N/A

Specimen: serum

No fasting required. Specimen should be collected prior to administration of next antibiotic dose when possible (trough level). Ensure proper aseptic technique during collection to avoid contamination.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

This test is critical for managing antibiotic therapy. Low levels may indicate poor absorption or resistance, while high levels could signal toxicity or incorrect dosing. It helps prevent overuse of antibiotics and ensures you receive the most effective treatment for your infection.

Short name

Ceftriaxone Level (Serum)

Frequently asked questions

Why might my doctor want to check my ceftriaxone levels frequently?
If you’re receiving IV ceftriaxone for a serious infection, frequent monitoring helps ensure the drug is working as intended. This is especially important for patients with kidney or liver issues, who may need dose adjustments to avoid side effects.
Can food or other medications affect this test?
No, food or most over-the-counter medications won’t interfere with this test. However, if you’re taking other antibiotics or have kidney/liver problems, your doctor may adjust your treatment based on the results.
What are the most common side effects of ceftriaxone?
Common side effects may include mild stomach upset, diarrhea, or allergic reactions (like rash or itching). Rare but serious side effects include kidney problems or nerve damage. If you experience severe symptoms like swelling, difficulty breathing, or persistent pain, seek medical attention immediately.
  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