Homocysteine (Total), Methylmalonic Acid, and Methylcitric Acid, Blood Spot
Use
This test is particularly useful as a second-tier assay of newborn screening specimens when abnormal levels of propionyl carnitine or methionine concentrations are detected in a primary newborn screen. It helps in the diagnosis of inborn errors of methionine and propionic acid metabolism, which can present with symptoms such as failure to thrive, developmental delay, intellectual disability, and other metabolic disorders. The test measures homocysteine, methylmalonic acid, and methylcitric acid, which are specific markers for these metabolic conditions.
Special Instructions
The test requires specific collection methods for accurate results. It is preferable to collect specimens using the Blood Spot Collection Card (Filter Paper), with sodium heparin as the collection medium if necessary. The collected blood spots need to be dried at ambient temperature and should not be exposed to heat or direct sunlight. This test serves as a follow-up for abnormal newborn screening results to confirm disorders of methionine and propionic acid metabolism.
Limitations
This test is sensitive to proper collection and handling procedures. False negatives may occur in individuals undergoing treatment for related metabolic disorders as their levels might normalize. Additionally, this test is not FDA approved but is performed in a manner consistent with CLIA requirements. Insufficient specimens or those showing serum rings are subject to rejection. Therefore, at least 2 circles on the filter paper should be completely filled to avoid sample rejection.
New York Approved
Methodology
Mass Spectrometry (LC-MS/MS)
Biomarkers
LOINC Codes
- 100765-7
- 54301-7
- 82385-6
- 82386-4
- 18771-6
- 59462-2
Result Turnaround Time
3-6 days
Related Documents
For more information, please review the documents below
Specimen
Whole Blood
Volume
2 Blood spots
Minimum Volume
1 Blood spot
Container
Blood Spot Collection Card (Filter Paper)
Collection Instructions
Do not use device or capillary tube containing EDTA or ACD to collect specimen. Sodium heparin is acceptable but must be spotted on card the same day as collected. Completely fill at least 2 circles on the filter paper card using blood from a heel or finger stick. Let blood dry on filter paper at ambient temperature in a horizontal position for a minimum of 3 hours. Do not expose specimen to heat or direct sunlight and do not stack wet specimens. Keep specimen dry.
Storage Instructions
Whole blood specimen should be stored on filter paper at ambient, refrigerated, or frozen temperatures.
Causes for Rejection
Shows serum rings, insufficient specimen
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | FILTER PAPER |
| Refrigerated | FILTER PAPER |
| Frozen | FILTER PAPER |