Complete Blood Count (CBC) Test: What It Is, Why It Is Done, and What Results Mean
This test detects a specific genetic variant (c.1236C>T) in the ABCB1 gene that affects how your body processes certain medications.
{"The ABCB1 gene helps transport drugs in and out of cells","The c.1236C>T variant may affect drug response and effectiveness","Results help doctors personalize medication choices","A simple blood sample is all that's needed","This test does not diagnose disease, but guides treatment"}
Key facts at a glance
- LOINC
- 104281-1
- Short code
- ABCB1 1236C>T
- Synonyms
- ABCB1 gene.c.1236C>T Bld/T Ql
- Category
- chemistry
- Sample
- whole-blood
- Container
- EDTA tube (purple top) - 4 mL minimum
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 18 years
- Method
- molgen
- CPT
- 81215
- SNOMED
- 371468003
- Specimen volume
- 2-5 mL whole blood
- Stability
- Room temperature: 72 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 30 days. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 72–168 hours
- Order
- routine
What is this test? A complete blood count (CBC) is a common blood test that measures the different cells in your blood, including red blood cells, white blood cells, and platelets, to help evaluate your overall health.
The ABCB1 gene c.1236C>T test is a genetic test that looks for a specific change (variant) in your ABCB1 gene. This gene contains instructions for making a protein called P-glycoprotein (P-gp), which acts like a pump to move certain drugs in and out of cells throughout your body. The c.1236C>T variant is one of the most common genetic variations in the ABCB1 gene and can affect how well this protein works.
Why might I need this test? Your healthcare provider may order a CBC as part of a routine checkup, to help find the cause of symptoms such as fatigue, weakness, fever, or unusual bruising, or to monitor a condition like anemia or an infection.
Your doctor may order this test to help predict how you might respond to certain medications. The ABCB1 gene variant can influence how your body processes drugs like some chemotherapy agents, steroids (such as dexamethasone), certain antidepressants, and some heart medications. Knowing your genetic makeup can help your doctor choose the most effective medication or adjust the dose for better treatment outcomes.
How is the test done? A healthcare professional will clean your skin and draw a small sample of blood from a vein in your arm, usually on the inside of your elbow, using a thin needle. The sample is then sent to a laboratory for analysis.
A healthcare professional will collect a small sample of your blood, usually from a vein in your arm. The sample is then sent to a specialized laboratory where scientists analyze your DNA to detect the presence or absence of the c.1236C>T variant in the ABCB1 gene. The results are typically available within a few days to a couple of weeks.
What do the results mean? Your results show whether your red blood cell, white blood cell, and platelet counts fall within normal ranges. Abnormal levels may suggest conditions such as anemia, infection, inflammation, or bleeding problems, and your provider will explain what your specific values mean for your care.
The test result will show whether you have the normal version (wild-type), the variant version, or both (heterozygous) of the ABCB1 gene at position 1236. Having the variant may mean that the P-glycoprotein functions differently in your body, which can affect drug absorption, distribution, and elimination. Your doctor will interpret these results together with your medical history and other factors to guide your treatment plan.
Reference range
Result reported as presence or absence of the ABCB1 c.1236C>T variant. Reference range: Wild-type (homozygous CC), Heterozygous (CT), or Homozygous variant (TT). Clinical significance based on genotype interpretation.N/A
No special preparation required. Inform patient that this is a genetic test for variant detection. Standard precautions for venipuncture apply.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The ABCB1 c.1236C>T variant can influence drug response in several ways: it may affect the effectiveness of certain chemotherapy drugs by altering drug transport into cancer cells; it can impact the absorption and distribution of various medications across the blood-brain barrier; and it may contribute to drug resistance in some conditions. This genetic information helps healthcare providers make more informed decisions about medication selection and dosing, particularly for medications known to be affected by ABCB1 function. However, this test is just one factor among many that influence drug response, and results should always be interpreted by a qualified healthcare professional.
Frequently asked questions
Is this test the same as a drug sensitivity test?
Will insurance cover this genetic test?
Does this test tell me if I have a disease?
How often is this variant found in the population?
Can my results change over time?
Sources
- 1
- 2
- 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