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Serum or Plasma Test for Substance Concentration (e.g., Antibiotic, Antimicrobial, or Drug Monitoring)

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

This test measures the amount of a specific substance in your blood, often used to check levels of medications, infections, or other compounds.

Quick summary

["This test helps doctors monitor your treatment or health status by measuring key substances in your blood."]

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

Key facts at a glance

LOINC
10090-9
Short code
ST I-Amp 6ms L-V3
Synonyms
ST I-Amp 6ms L-V3
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ekg
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

What This Test Measures

Your blood sample will be tested for a particular substance—such as an antibiotic, antiviral, or other medication—using a sensitive lab method. The test detects how much of this substance is present in your serum or plasma.

Why It’s Done

Doctors order this test to ensure you’re taking the right dose of a medication, to check for infections, or to monitor conditions like drug toxicity or exposure to harmful substances.

Sample Collection and Preparation

A blood sample is drawn from your arm, and the blood is processed into either serum (after clotting) or plasma (after centrifugation). The lab then analyzes the sample for the target substance.

What to Expect Before the Test

No special preparation is needed, but you may avoid certain foods or medications for a few hours before testing, depending on the substance being measured.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

This test plays a critical role in managing conditions like infections, drug therapy adherence, or detecting exposure to toxins. It helps prevent overuse of medications or missed doses by providing real-time data on substance levels in your blood.

Short name

None

Frequently asked questions

How long will it take to get my results?
Results are typically available within 1–3 business days, depending on the lab and complexity of the test. Follow-up with your healthcare provider will help interpret the results.
What does a high or low result mean?
Results may indicate whether your substance levels are too high (risking side effects) or too low (needing adjustment). Your doctor will discuss this with you based on your medical history and treatment plan.
Can I eat or drink before this test?
Check with your doctor or lab about any dietary restrictions, as some substances require fasting or avoiding certain foods/drinks before testing.
  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