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Serum or Plasma Concentration of Promethazine

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

This test measures the amount of promethazine, a medication used to treat allergies, insomnia, or as an anti-emetic, in your blood.

Quick summary

["Knowing your promethazine level helps doctors monitor your dose and side effects."]

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

Key facts at a glance

LOINC
75270-9
Short code
Promethazine Ser/Plas/Urn Ql Scn
Synonyms
Promethazine Ser/Plas/Urn Ql Scn
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
screen
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 healthcare provider may order this test if you’re taking promethazine regularly, experiencing unusual symptoms (like dizziness, confusion, or slow heart rate), or if you have concerns about drug interactions or toxicity.

What to Expect Before the Test

No special preparation is needed. You may have blood drawn from a vein in your arm, similar to other blood tests. If you’re on a blood thinner, let your provider know before the test.

What the Results Mean

Results are interpreted based on your symptoms, medication history, and overall health. Abnormally high or low levels may signal issues like overdose, poor metabolism, or drug resistance.

Common Reasons for Testing

This test is often used to assess therapeutic drug monitoring (TDM) for promethazine, especially in cases of suspected overdose, drug interactions, or persistent side effects.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Promethazine Level

Frequently asked questions

What Are My Next Steps If My Results Are Abnormal?
If your results are outside expected ranges, your doctor will discuss next steps, which may include adjusting your medication dose, investigating other health conditions, or further testing to understand why levels changed.
How Long Will It Take to Get Results?
Results are typically available within 1–3 business days, depending on your lab’s processing time. Your provider will contact you with the final report.
Can I Avoid This Test?
If you’re not experiencing symptoms or have no known risk factors, your doctor may not routinely order this test unless you’re on long-term promethazine therapy or have specific concerns.
  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