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INTRODUCTION: What is
Homocysteine?
When the essential amino acid methionine is metabolized, one of the
products formed is homocysteine, itself a sulphur containing amino acid.
Homocysteine is further metabolized by either re-methylation, requiring vitamin
B12 and folic acid, or by a transulfuration pathway involving a vitamin
B6
dependent enzyme. Normally homocysteine is rapidly metabolized enzymatically,
preventing its build up in circulation.
REFERENCE VALUES of
homocysteine in adults
Reference value for adult male or female is between 5-15
µmol/L. Men have
higher values than women. Post menopausal women also have higher values than
premenopausal women.
Role in diseases
1. Cardiac diseases
Epidemiological studies have shown that high plasma Homocysteine
concentrations may be a risk factor of coronary artery disease (CAD). A 5 µmol/L
increase in plasma homocysteine has been estimated to raise the risk of
coronary heart disease by as much as an increase in the serum cholesterol
level of 0.5 µmol/L (20 mg/100 ml).
Elevated total homocysteine levels are frequently
found in patients with
arteriosclerosis affecting coronary, cerebral and peripheral arteries. Through
formation of the reactive oxygen species, high levels of homocysteine cause
damage to the endothelial lining of vessels predisposing them to thrombosis
and formation of atherosclerotic plaques.
2. Renal Diseases
Patients with chronic renal disease show increased morbidity and mortality
due to atherosclerotic Cardio Vascular Diseases (CVD). Although these patients
may lack some of the vitamins involved in the metabolism of homocysteine,
increased levels of total homocysteine are mainly due to impaired removal of
homocysteine from the blood by the kidney.
3. Diabetes Mellitus
Diabetes Mellitus is associated with a sharply increased risk of CVD and
mortality. Plasma total homocysteine concentration has been found to be a
significant predictor of mortality in NIDDM patients with/without albuminuria.
4. Obstetrics
Increased plasma homocysteine concentration during
pre-eclampsia may advance
endothelial dysfunction, a central feature of the patho-physiology, by
promoting oxidative stress. Elevated homocysteine concentration during
pregnancy is also associated with recurrent spontaneous abortion, eclampsia,
intra-uterine growth retardation, placental infarction and neural tube
defects.
Can the level
of homocysteine be reduced in the human body?
Plasma folate and vitamin B12 concentrations have been reported to be
inversely associated with plasma homocysteine values and supplementation with
folate, vitamin B6, and vitamin B12 has been shown to reduce plasma
homocysteine concentration.
Screening
for homocysteine is advisable in:
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A strong family history of atherosclerotic disease.
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Early onset (before age 50 years) of
symptoms of coronary
heart disease,
cerebrovascular disease or peripheral vascular disease.
Specimen
requirements
3 ml of blood in an EDTA
vial in the fasting state.
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