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Serum or plasma concentration of cysteine

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

This test measures the amount of cysteine, an amino acid important for protein synthesis and antioxidant defense, in your blood.

Quick summary

["Cysteine helps protect cells from oxidative stress and supports healthy tissue function."]

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

Key facts at a glance

LOINC
59253-5
Short code
Hycs-Cys diS Ur-sCnc
Synonyms
Hycs-Cys diS Ur-sCnc
Category
chemistry
Sample
urine
Container
Sterile urine container
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your healthcare provider may order this test to evaluate conditions affecting amino acid metabolism, such as certain genetic disorders (e.g., cystinosis), kidney function, or to monitor treatment for metabolic or inflammatory diseases. It may also be part of a broader metabolic screening.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours if your blood is drawn early in the morning. Avoid strenuous activity or excessive caffeine on the day of testing.

During the Test

A healthcare professional will draw blood from a vein in your arm. You may feel a brief pinch or discomfort, but it typically lasts only a few seconds. The test itself takes just a few minutes.

After the Test

You can resume normal activities immediately. Apply gentle pressure to the site to stop any bleeding, and check for signs of infection (e.g., redness, swelling). Report any unusual symptoms to your provider.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Elevated cysteine levels may indicate inherited metabolic disorders, kidney disease, or certain genetic conditions. Low levels could suggest malnutrition or rare metabolic syndromes. Your provider will interpret results in the context of your symptoms, medical history, and other tests.

Short name

Cysteine Level

Frequently asked questions

What does a high or low cysteine level mean?
A high level may signal conditions like cystinosis (a genetic disorder causing cystine buildup) or kidney problems. A low level might suggest poor nutrition or metabolic imbalances. Your provider will discuss findings with you.
How often should I get this test?
Frequency depends on your health needs. If you have a known condition (e.g., cystinosis), your provider may recommend regular monitoring. Otherwise, this test is rarely routine unless symptoms arise.
Can diet or supplements affect cysteine levels?
Yes—protein-rich foods (e.g., eggs, meat) and certain supplements (like cysteine-containing medications) may influence results. Avoid recent protein-heavy meals before testing if instructed.
  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