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Serum or plasma mass concentration of methylthioadenosine phosphorylase (MTAP)

Published: August 9, 2026Updated: August 17, 2026

This test measures the amount of methylthioadenosine phosphorylase, an enzyme involved in purine metabolism, in your blood.

Quick summary

["Understanding your MTAP levels may help assess certain genetic or metabolic conditions."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
81624-9
Short code
MTX-PG5 RBC-sCnc
Synonyms
MTX-PG5 RBC-sCnc
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Ref low
4.2
Ref high
5.9
Critical range
2 N/A – 7 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
85041
SNOMED
900000000000003001
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Is Done

Your healthcare provider may order this test if you have symptoms or a family history suggestive of metabolic disorders, such as Lesch-Nyhan syndrome or other genetic conditions affecting purine metabolism. It may also be part of diagnostic workup for unexplained neurological symptoms or blood abnormalities.

What to Expect Before the Test

No special preparation is typically needed. You may have a blood sample drawn from a vein in your arm, similar to other routine blood tests. If you’re on blood thinners, inform your provider beforehand.

What the Test Results Mean

Results are interpreted based on your clinical picture and symptoms. Abnormal levels may indicate genetic disorders affecting enzyme function, but further testing or evaluation is needed to confirm a diagnosis.

Common Causes of Abnormal Results

Low levels may suggest inherited enzyme deficiencies or certain metabolic syndromes. High levels are less common but could relate to rare genetic variants or enzyme dysfunctions.

Reference range

Adult males: 4.2-5.9; Females: 3.8-5.1 x 10^12/LN/A

Specimen: whole-blood

No special preparation required. Stay well hydrated.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

MTAP Level

Frequently asked questions

What does a low MTAP level mean?
A low MTAP level may indicate an inherited enzyme deficiency, such as Lesch-Nyhan syndrome, which can lead to metabolic imbalances. Your provider will discuss next steps based on your symptoms and test results.
How is this test different from other blood enzyme tests?
Unlike more commonly tested enzymes (e.g., liver or muscle enzymes), MTAP is a rare enzyme measured specifically for genetic metabolic disorders. It’s not a routine screening test but may be ordered for suspected hereditary conditions.
Can diet or medications affect MTAP levels?
Dietary factors or medications typically do not directly affect MTAP levels, as it’s an enzyme involved in cellular metabolism. However, genetic predisposition is the primary driver of variations in this test result.
  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 17, 2026. · Read our editorial policy