Plasma Total Homocysteine

Clinical Utility:

This HPLC assay is a quantitative test diagnostic for several metabolic diseases. These include cystathionine-b-synthase deficiency (CBS) and disorders of vitamin B₁₂ or folate metabolism.

Increased plasma homocysteine is also a major independent risk factor for venous thromboembolism and atherosclerosis. Therefore, determination of homocysteine in plasma is increasily of interest in cardiovascular risk assesment.

About 70% of homocysteine is bound to plasma proteins. The free forms include homocystine (homocysteine disulfide) and homocysteine-cysteine mixed disulfide, and a trace of free homocysteine. This procedure measures all forms found in plasma.

Specimen Types:

The most appropriate and convenient sample material is a plasma sample collected in EDTA tube. The collection of blood has to be done under a strict protocol as follows:

3 ml of venous blood is to be collected in labeled purple top tubes and mixed. The samples should be placed immediately on wet ice. Plasma should be isolated in less than one hour from these samples by centrifugation at 3-4,000 rpm at 20-25⁰C. The separated plasma is to be transferred to a labeled plasma tube, and immediately frozen. All these steps are critical. These frozen samples should be delivered to MSL as soon as possible. Cooling during transfer is advisable especially during the summer months.

Turn-around Time:

Routine: 7-14 days from receipt of sample

Stat: No stat samples are accepted.

Test Limitations & Interfering Substances:

No limitations or interference are known.

Report Format:

The result is given in a one-page report that details the patient information, date of sample, date of analysis and a result code, which could be one of three:

"NOT REMARKABLE" "QUESTIONABLE" "ABNORMAL"

The value for total homocysteine will be provided and compared with normal ranges in males and females. Interpretation of questionable or abnormal results will be provided. Recommendation for follow-up samples, or further tests, which are needed for confirmation, will be indicated.