Which laboratory test is ordered to determine the presence of the amino acid that can contribute to cardiovascular disease and stroke?

• A. Antidiuretic hormone
• B. Ceruloplasmin
• C. Homocysteine
• D. Cryoglobulin

Answer: (C)

Elevated homocysteine levels are a risk factor for cardiovascular disease and stroke. The test ordered to determine the presence of this amino acid is a plasma homocysteine level. Homocysteine is a sulfur-containing amino acid produced during methionine metabolism; when it rises, it can damage the vascular endothelium, promote LDL oxidation, and enhance thrombosis, all contributing to atherosclerosis and cerebrovascular events. Levels can be influenced by vitamins B6, B12, and folate, and correcting deficiencies can lower the level. The other options are not amino acids tied to cardiovascular risk: antidiuretic hormone is a hormone regulating fluid balance, ceruloplasmin is a copper-transport protein, and cryoglobulins are immunoglobulins that precipitate in cold.