Serum homocysteine raised in both early cobalamin and folate deficiency but may be raised in other conditions, e.g., chronic renal disease, alcoholism, smoking, pyridoxine deficiency, hypothyroidism, and therapy with steroids, cyclosporine, and other drugs
also higher in serum than in plasma, in men than in premenopausal women, in women taking hormone replacement therapy or in OCP users, and in elderly persons and patients w/ several inborn errors of metabolism affecting Es in trans-sulfuration pathways of homocysteine metabolism