Homocysteine, Total Quantitative, Dried Blood Spot

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Condition Description

Determination of total homocysteine is essential for the diagnosis and follow up of patients with homocystinuria due to beta-cystathionine synthase deficiency, MTHFR deficiency, certain types of cobalamin deficiency, and folate deficiency. Mild to moderate elevations and decreases of methionine levels detected by routine newborn screening (NBS) are possible indications of hyperhomocysteinemia. However, methionine levels in blood are often affected by many factors, such as the use of TPN, methionine rich formula, and immature liver function. Thus, by directly measuring total homocystine in dried blood spots (DBS) as a 2nd tier test provides a specific diagnostic tool for increasing the sensitivity and decreasing the false positive rate of NBS for homocystinemia.

The majority of cases of homocystinuria are due to deficiency of the enzyme cystathionine synthase, which causes an accumulation of methionine, homocystine, and various metabolites of homocystine and a decrease of cystathionine. Clinical manifestations vary in degree, type, and age of onset. They include diffuse thromboembolism, dislocation of the optic lens, osteoporosis, tall stature due to thin, lengthened long bones, seizures, psychiatric disturbances, and mental retardation. MTHFR deficiency and certain types of cobalamin deficiency could present with low methionine, high homocystine, with or without concurrent methymalonic aciduria. All of these conditions can be effectively treated if they are identified early in life.

Indications

This test is indicated for:
  • Individuals with high methionine level by routine NBS
  • Individuals with low methionine level by routine NBS
  • Individuals with C3 elevation by routine NBS
  • Individuals suspected to have homocystinuria or hyperhomocystinemia

Methodology

Liquid Chromatography-Mass Spectrometry (LC-MS/MS)

Detection and Reference Range

Detection
This test is very sensitive for homocysteine but should be interpreted in light of clinical symptoms and nutritional status.
Reference Range
<15 µmol/L

Specimen Requirements

Type: Dried Blood Spot

Specimen Requirements:

Peripheral blood from finger prick or heel stick spotted on filter paper, completely saturating the circle. Air dry the sample.

Specimen Collection and Shipping: Do not expose specimen to heat or direct sunlight. Keep the specimen dry. Ship sample at room temperature with overnight delivery.

Special Instructions

Please indicate any medications or dietary changes on the test requisition form.
  • Organic Acid Analysis (OA), Plasma Amino Acids (AA), and Urine Amnio Acids (UA) are used in the diagnosis and evaluation of patients with metabolic conditions.
  • Homocysteine, Total Plasma (HO)
  • Cystathionine Beta-Synthase Gene Sequencing (EY)

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