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homocysteine in serum/plasma

Indications: - no role for routine measurement [2] Reference interval: - 5-15 umol/L Clinical significance: Increased homocysteine levels are a risk factor* for: 1) atherosclerosis* including: a) coronary artery disease [5] b) cerebrovascular disease$ 2) perhaps dementia%, including Alzheimer's disease [4] 3) venous thrombosis# * risk appears to increase at levels of > 8 umol/L modest risk factor [6] # Risk increased 4-fold for homocysteine levels > 18 umol/L [2] % 2-fold risk of dementia for homocysteine levels of 14 umol/L $ NO benefit of lowering serum homocysteine in secondary stroke prevention [7] Toxicity: 1) directly injures endothelial cells 2) promotes growth of smooth muscle cells 3) increases thrombogenicity 4) inhibits thrombolysis Determinants of homocysteine levels include: 1) diet high in meat & milk protein increase homocysteine 2) hereditary enzymatic factors 3) renal function 4) dietary & supplementary folic acid can decrease homocysteine levels 5) vitamin B6 6) vitamin B12 7) pharmaceutical agents Increases: - vitamin B12 deficiency - folate deficiency - most sensitive marker for folate deficiency [2] - pharmaceutical agents - niacin - colestipol - L-dopa Methods: Assays for homocysteine: 1) HPLC 2) another assay for homocysteine/homocystine is a modification of the cyanide nitroprusside test, based upon reaction of sodium nitroprusside with sulfhydryl compounds including cysteine & homocysteine to produce a red-purple product. Oxidized disulfides do not react, but must first be reduced to the free thiol form with alkaline sodium cyanide. A modification of the cyanide nitroprusside test is used to distinguish between cysteine & homocysteine. By substituting AgNO3 for sodium cyanide as the reducing agent, homocystine can be reduced to its thiol form (homocysteine) while cystine remains as the disulfide. Homocysteine then reacts with sodium nitroprusside to become purple-pink. Specimen: 1) serum/plasma 2) EDTA tube centrifuged in < 30 minutes to prevent release from RBC

Related

homocysteine homocysteine in urine hyperhomocysteinemia

Specific

homocysteine in serum/plasma post methionine

General

homocysteine in body fluid

References

  1. Tietz Textbook of Clinical Chemistry, 2nd ed. Burtis CA & Ashwood ER (eds), WB Saunders Co, Philadelphia PA, 1993
  2. Medical Knowledge Self Assessment Program (MKSAP) 11, 17. American College of Physicians, Philadelphia 1998, 2015
  3. Carmel R, Ann Rev Med 51:357, 2000
  4. Journal Watch 22(7):56-57, 2002 Seshadri S et al, N Engl J Med 346:476, 2002
  5. Journal Watch 22(12):92, 2002 Ridker PM et al, Circulation 105:1776, 2002
  6. Journal Watch 22(24):181, 2002 Homocysteine Studies Collaboration, JAMA 288:2015, 2002 Kirk M et al, JAMA 288:2023, 2002 Wilson PWF, JAMA 288:2042, 2002
  7. Journal Watch 24(5):8, 2004 Toole JF et al, JAMA 291:565, 2004 PMID: 14762035
  8. Panel of 6 tests Laboratory Test Directory ARUP: 30133
  9. Panel of 16 tests Laboratory Test Directory ARUP: 30268
  10. Homocysteine, Total Laboratory Test Directory ARUP: 99869

Component-of

methylmalonate/homocysteine in serum/plasma