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18qchromdelbldt

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

A genetic test that detects deletions in the long arm (q) of chromosome 18 using molecular genetics methods.

Quick summary

{"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"}

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

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

What is This Test?

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.

How is the Test Performed?

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.

Why Might I Need This Test?

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

Specimen: whole-blood

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.

◆Associated findings2

Frequently asked questions

How long does it take to get results?
Results from chromosome deletion testing typically take 2-4 weeks, but may take longer depending on the specific laboratory methods used and whether confirmatory testing is needed.
Is the test painful?
The blood draw may cause brief discomfort, similar to a pinprick. The procedure is generally well-tolerated and takes only a few minutes.
Will this test tell me about my risk for other conditions?
This specific test identifies deletions on chromosome 18q. It does not检测其他染色体的问题 unless the laboratory is specifically looking for them. If you're interested in broader genetic screening, discuss other options with your doctor or genetic counselor.
Do I need to fast before this test?
No, fasting is not required for this genetic blood test. You can eat and drink normally before the test.
Can this test determine if I'm a carrier?
This test detects deletions in the genetic material. If you are a parent of a child with an 18q deletion, genetic testing can help determine if the deletion was inherited or occurred spontaneously (de novo). A genetic counselor can help interpret these results for your family.
  1. 1
    Genetics Home Reference - 18q deletion syndromeSource
  2. 2
    LOINC Code ReferenceSource
  3. 3
    National Human Genome Research Institute - Chromosome 18q DeletionSource

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