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Acyclovircsfmcnc

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

This test measures the amount of acyclovir antiviral medication in the cerebrospinal fluid to help doctors ensure proper dosing during treatment of brain infections.

Quick summary

{"Measures acyclovir levels in the fluid surrounding the brain and spinal cord","Helps doctors ensure you receive the right dose to treat herpes infections of the brain","Performed through a lumbar puncture (spinal tap)","Used mainly for patients with herpes encephalitis or other CNS herpes infections","Results help prevent both treatment failure and drug toxicity"}

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

Key facts at a glance

LOINC
80121-7
Short code
ACV-CSF
Synonyms
Acyclovir CSF-mCnc
Category
chemistry
Sample
csf
Container
Sterile polypropylene cryovial
Units
N/A
Ref low
0.8
Ref high
2.2
Critical range
— – 5 N/A
Fasting
false
Population
adult
Sex
all
Age range
0–120 years
Method
Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) or High-Performance Liquid Chromatography (HPLC)
CPT
80125
SNOMED
371949009
Specimen volume
0.5-1.0 mL CSF
Stability
Room temperature: 24 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 30 days
Hemolysis max
200
TAT
24–72 hours
Order
routine

What is this test?

The Acyclovir in CSF test measures how much of the antiviral medication acyclovir is present in your cerebrospinal fluid (CSF). CSF is the clear, protective fluid that surrounds your brain and spinal cord. This test is not a routine blood test—it requires a special procedure called a lumbar puncture to collect the fluid.

Why is it done?

Doctors order this test primarily when treating serious herpes virus infections that affect the central nervous system, such as herpes encephalitis (brain infection) or neonatal herpes. Acyclovir is the main treatment for these conditions, but doctors need to confirm the medication is reaching the CSF in sufficient amounts to fight the infection. This is called therapeutic drug monitoring.

How is the sample collected?

The sample is collected through a lumbar puncture, also known as a spinal tap. During this procedure, you will lie on your side or sit leaning forward. A healthcare provider will clean your lower back area, inject a local anesthetic, and then insert a thin needle between two vertebrae in your lower spine to collect a small amount of CSF. The procedure usually takes 15-30 minutes.

What do the results mean?

Results are reported as either detectable or undetectable, or sometimes as a concentration value. Therapeutic levels mean the drug has reached the CSF in amounts expected to treat the infection effectively. Low or undetectable levels may indicate the dose needs adjustment. Your doctor will interpret your results based on your specific condition, timing of the dose, and other factors.

Reference range

Therapeutic range: 0.8-2.2 mcg/mL; Toxic level: >5.0 mcg/mLN/A

Specimen: csf

No special preparation required. Collect CSF via lumbar puncture following standard aseptic technique.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings2

Frequently asked questions

How long does it take to get results?
Results are typically available within 1-3 days, as the test is usually performed by specialized laboratories that perform mass spectrometry or other advanced analytical methods.
Does the lumbar puncture hurt?
You will feel a pinch from the anesthetic injection, and may feel pressure or mild discomfort during the needle insertion. Most patients tolerate the procedure well. Some may experience a headache afterward, which can be managed with rest and fluids.
Do I need to fast before this test?
No fasting is required. However, inform your doctor about all medications you are taking, especially any antivirals, as they may affect the test results.
What happens if my levels are too low?
Low levels may indicate that your current dose is not reaching effective concentrations in the CSF. Your doctor may increase your dose, change how often you receive it, or ensure you are receiving it properly through IV.
Can this test detect if I have a herpes infection?
No, this test measures drug levels, not the virus itself. Other tests like CSF PCR are used to detect the presence of herpes virus in the CSF. This test is used to monitor treatment, not to diagnose.
  1. 1
    MedlinePlus - AcyclovirSource
  2. 2
    Mayo Clinic Laboratories - Acyclovir, CSFSource
  3. 3
    UpToDate - Herpes simplex virus encephalitis: TreatmentSource

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