Chromosome 18q Deletion Test
A genetic test that detects deletions in the long arm (q) of chromosome 18 using molecular genetics methods.
{"This test looks for missing genetic material on chromosome 18q","It helps diagnose genetic conditions associated with 18q deletions","The test requires a simple blood sample","Results can guide medical management and genetic counseling","Results typically take several weeks to process"}
Key facts at a glance
- LOINC
- 46108-7
- Short code
- 18q Del
- Synonyms
- 18q Chrom Del Bld/T
- Category
- chemistry
- Sample
- whole-blood
- Container
- EDTA tube (lavender/purple top) for whole blood, or sterile tissue container for tissue samples
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 0 years
- Method
- molgen
- CPT
- 78200, 78201, or 78202 (Cytogenetic analysis codes); specific molecular codes may apply: 81405, 81406
- SNOMED
- 129300006 (Chromosome deletion) or 236190004 (Chromosome 18q deletion)
- Specimen volume
- 3-5 mL whole blood in EDTA tube; tissue: minimum 2-3 mm³
- Stability
- Whole blood: 24-48 hours at room temperature (18-25°C); 72 hours refrigerated (2-8°C). Tissue: process immediately or store at 2-8°C for up to 24 hours. Avoid freezing whole blood specimens.
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 168–336 hours
- Order
- routine
This test looks for a missing piece of genetic material, called a deletion, on the long arm (known as the q arm) of chromosome 18. It is commonly used to help diagnose 18q deletion syndrome, a genetic condition that can affect growth, development, muscle tone, and other body systems.
The 18q chromosome deletion test is a genetic test that looks for a missing piece (deletion) on the long arm (called the 'q' arm) of chromosome 18. Chromosomes are structures in our cells that carry genetic information (DNA). A deletion means a portion of the genetic material is missing. This test uses molecular genetics methods to detect these deletions with high precision.
The test is most often done using a blood sample drawn from a vein in your arm, or your child's arm. In some cases, a cheek swab or other tissue sample may be used. The sample is sent to a laboratory, where specialized techniques examine chromosome 18 closely for any missing segments.
A healthcare provider will collect a blood sample from a vein in your arm. For certain situations, a tissue sample may also be used. The sample is then sent to a specialized laboratory where molecular genetics techniques (such as chromosomal microarray analysis or fluorescent in situ hybridization (FISH)) are used to detect whether any genetic material is missing from chromosome 18q.
Your doctor may recommend this test if you or your child has unexplained developmental delays, intellectual disability, low muscle tone, growth problems, seizures, or distinctive facial features that could be linked to an 18q deletion. It may also be offered if a close family member is known to carry a chromosome 18q deletion or if prenatal findings raise concern.
This test may be ordered if a doctor suspects a genetic condition related to 18q deletion. It may be recommended for individuals with developmental delays, intellectual disabilities, distinctive facial features, growth problems, or other symptoms that suggest a chromosomal abnormality. The test may also be used for prenatal diagnosis if there is a family history or abnormal prenatal screening results.
Reference range
No 18q deletion detected. Result reported as 'Negative' or 'Deletion not identified'. Reference range is qualitative (presence or absence of deletion).N/A
No special preparation required. Standard venipuncture precautions. Inform laboratory of recent blood transfusions as this may affect results. Provide relevant clinical history including any known chromosomal abnormalities in family.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Chromosome 18q deletion syndrome (also known as 18q- syndrome) is associated with a range of possible symptoms including developmental delay, intellectual disability, characteristic facial features (such as a prominent forehead, deep-set eyes, and ear abnormalities), growth delays, low muscle tone (hypotonia), and immune deficiencies. Some individuals may also have hearing loss, vision problems, or heart defects. The specific symptoms and severity can vary significantly among individuals with 18q deletions.
This test is important because it provides a definitive genetic diagnosis, which can help guide appropriate medical care, early intervention services, and genetic counseling for the patient and their family. Understanding the specific deletion can also help predict associated health concerns and guide surveillance for potential complications.
Frequently asked questions
How long does it take to get results?
Is the test painful?
Will this test tell me about my risk for other conditions?
Do I need to fast before this test?
Can this test determine if I'm a carrier?
Sources
- 1
- 2LOINC Code ReferenceSource
- 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