Homocysteine in serum
The reference values of serum homocysteine concentration are: in women 5-12 μmol / l, in men - 5-15 μmol / l.
Homocysteine is a product of the exchange of amino acids( conversion of methionine to cysteine).Approximately 70% of plasma homocysteine is associated with
with albumin, 30% is oxidized to disulfide and only 1% is in a free state. The overwhelming majority of methods used to detect the level of homocysteine in the blood allow us to determine only the total content of the oxidized and reduced forms. The results of the analyzes depend to a large extent on the correctness of the blood sampling and the rate at which the serum is separated from the blood cells, as the blood cells continuously produce and release homocysteine.
High concentrations of homocysteine are the most important factor in the early development of atherosclerosis and thrombosis. Hyperhomocysteinemia is detected in 13-47% of IHD patients. Currently, the determination of serum homocysteine concentration is used as a marker for the development of IHD.The high concentration of homocysteine in the blood in patients with IHD is a clear harbinger of acute episodes that can lead to death. In terms of severity, hyperhomocysteinemia is divided into mild( 15-25 μmol / l), moderate( 25-50 μmol / l) and heavy( 50-500 μmol / l).In patients with coronary artery disease with a homocysteine concentration in the blood below 10 μmol / L, stenosis of the coronary arteries is usually less than 50%, with a level of 10-15 μmol / l - 80%, above 15 μmol / l - 90%.
Congenital homocysteinuria is a monogenic metabolic defect caused by a deficiency of methylene tetrahydrofolate reductase. The concentration of homocysteine in the blood plasma( 50-500 μmol / l) and its excretion in the urine are significantly increased in patients.
In a heterozygote for a cystathionine-P-synthetase defect, the homocysteine concentration in the blood is within normal limits, so a load test with methionine is used to detect the disease. This test is carried out in 2 stages. Initially, the control study. A sample of blood is taken immediately after breakfast and after 2, 4, 6 and 8 hours. Normally, the transient peak of homocysteine concentration increase occurs at an interval between 4 and 8 hours. On the second day, blood for the studies is taken immediately before the load and after 2, 4, 6and 8 hours after oral intake of methionine( 100 mg / kg).The test is considered positive if the concentration of homocysteine in the blood during this time interval exceeds the results of the control test by an amount equal to or exceeding 2 standard deviations [Guba S. et al., 1996].
Currently, the mechanisms that determine the role of increased concentration of homocysteine in the blood in the pathogenesis of atherosclerosis are actively discussed. A negative correlation was found between the concentrations in the blood of homocysteine and folate, as well as vitamins B6 and B12.Deficiency of these substances in the body is accompanied by an increase in the concentration of homocysteine in the blood. Use in the treatment of patients with hyper-homocysteinemia folates, vitamins B6 and B12( cofactors of metabolites of methionine metabolism) has shown their effectiveness. With effective therapy, the serum homocystene concentration should not exceed 10 μmol / l [Fomin V., 2001].
Hyperhomocysteinemia can also be one of the manifestations of the neoplastic process, particularly in breast, ovarian and pancreatic cancer, ALL.An increase in serum homocysteine concentration is possible with hypothyroidism, severe psoriasis, long-term use of theophylline preparations, estrogen-containing contraceptives, cytotoxic drugs( methotrexate) and antiepileptic drug
( phenytoin, carbamazepine), as a result of metabolic and absorption disorders of vitamin B12 and folic acid.