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|Performed by||China Basin Chemistry|
|In House Availability||Wednesday, and Saturday or Sunday (day shift)|
|Method||Chemiluminescent Immunoassay (Siemens Centaur)|
|Patient Preparation||An 8 hour fast before specimen collection is recommended because a protein-rich meal may increase results by 15%-20%.|
|Collection Instructions||Chill tube on ice before collection and transport on ice to lab.
If sample is not collected on ice, release of homocysteine from erythrocytes may increase levels by approximately 10% per hour at room temperature. (Clin Chem 50:3-32, 2004)
|Container type||Light Green top (on ice) (Gold top on ice acceptable)|
|Amount to Collect||2 mL blood|
|Sample type||Heparinized Plasma (serum acceptable)|
|Preferred volume||1 mL serum or plasma|
|Min. Volume||0.5 mL serum or plasma|
|UCSF Rejection Criteria||Not delivered on ice|
|Processing notes||Centrifuge immediately and refrigerate plasma or serum.
If sample was not received on ice append the following specimen comment: "Specimen not received on ice, may cause falsely elevated result in some cases"
|Turn around times||1-4 days|
|Additional information||Elevated levels are a risk factor for coronary artery disease and vascular thrombosis. The test for total plasma homocysteine may be used to screen for conditions causing homocystinuria. However, for cystinuria, order quantitative urine cystine.
Homocystinuria due to severe homozygous defects in the cystathionine beta synthase gene (or rare defects in other genes involved in the metabolism of sulfur-containing amino acids) may be associated with plasma homocysteine levels > 100 umol/L. Note that renal disease or deficiency in vitamin B12 or folate may also lead to similar elevations, although the C677T MTHFR mutation does not.
Homocysteine is measured as the sum of free homocysteine, homocysteine released by reduction from disulfides such as homocystine and cysteine-homocysteine, and homocysteine bound to serum proteins. "Total" homocysteine is sometimes signified by the abbreviations tHcy or Hcys or the term "Homocyst(e)ine".
Patients taking methotrexate, nicotinic acid, theophylline, nitrous oxide or L-dopa can have elevated levels serum or plasma homocysteine levels. S-adenosyl-methionine cross reacts in the Hcy assay (see lab procedure link)
Reference ranges for adults based on manufacturer's reference range, results of the National Health and Nutrition Examination Survey reported by Ganji and Kafai, Am J Clin Nutrition, 84:989-994, 2006, and in- house testing of laboratory personnel. tHcy results tend to run 1 – 4 units lower in children < 15 years of age ( Soldin et al, Clinical Biochemistry 41:937-942, 2008). Hyperhomocysteinemia is classified as moderate (15 – 30 umol/L), intermediate (30 – 100 umol/L), or severe (>100 umol/L). For further information on homocysteine testing, see Refsum et al, Annual Rev Medicine 49:31-62, 1998 and Maron et al, Clin Lab Med 26:591-609, 2006
|Medical Necessity?||Yes. Click here for more information|
|Last Updated||12/19/2012 4:30:33 PM|
|Lab Procedure Link||Click here for Procedure|
If you have additional questions regarding this test, please call: 415-353-1667