C-reactive protein (CRP) concentration in serum/plasma
This test measures the level of C-reactive protein, a protein produced by the liver in response to inflammation in your body.
["CRP helps doctors assess inflammation, often used to monitor conditions like infections, autoimmune diseases, or after surgery."]
Key facts at a glance
- LOINC
- 73975-5
- Short code
- CD158a
- Synonyms
- CD158a cells NFr Spec
- Category
- chemistry
- Sample
- serum
- Container
- Lavender-top (EDTA) or sodium heparin tube for flow cytometry; sterile collection tube
- Units
- N/A
- Ref low
- 3
- Ref high
- 15
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 1–99 years
- Method
- Flow cytometry
- CPT
- 86359
- SNOMED
- 399130001
- Specimen volume
- 3-5 mL of whole blood
- Stability
- Specimen should be processed within 24-48 hours of collection when stored at room temperature (18-25°C). Do not refrigerate if performing live cell analysis.
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 24–72 hours
- Order
- routine
Why CRP Matters in Your Health
CRP is a marker that signals whether your body is fighting inflammation. High levels may indicate an infection, injury, or conditions like arthritis or heart disease. Your doctor may order this test to check for these issues or to monitor treatment progress.
How the Test Works
A small blood sample is taken from your arm. The lab then measures the amount of CRP in your serum or plasma using a sensitive test method, often an immunoassay or nephelometry technique.
When You Might Need This Test
Doctors may recommend CRP testing if you have symptoms of inflammation, such as fever, joint pain, or swelling. It’s also used before or after surgeries, during pregnancy, or to check for conditions like lupus, rheumatoid arthritis, or heart disease.
What to Expect Before the Test
No special preparation is needed for most CRP tests. However, if your doctor has specific instructions—for example, avoiding certain foods or medications—follow them closely. For example, some tests may require fasting or avoiding aspirin or ibuprofen for a day or two before the blood draw.
Reference range
Reference range varies by laboratory; results reported as percentage of lymphocytes and absolute count of CD158a+ NK cells. Typical reference interval: 3-15% of total lymphocytes; absolute count varies by age.N/A
No special patient preparation required. Fasting is not required prior to specimen collection.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
CRP (Serum/Plasma)
Frequently asked questions
What does a high CRP level mean?
What does a low CRP level mean?
Can CRP levels change over time?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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