An example of a diagnostic reagent is uric acid (U-6000), which is used as a standard in the enzymatic quantification of uric acid in blood. Uric acid is the end product of the purine metabolism in humans. Therefore the measurement of uric acid in plasma and urine gives information about many metabolic disorders such as gout and renal stones or familial nephritis [Sebesta et al., 1994].
The carnosinase assay, which uses L-carnosine (beta-alanyl-L-hystidine) (C-2000) as substrate and measures the level of carnosinase in the human serum, is another diagnostic test. Several methods have been described to determine the carnosinase activity [Schoen et al., 2003]. Burgess et al. (1975) described a complete absence of plasma carnosinase activity in patients with proven urea cycle defects. Bando et al. (1986) observed a reduced carnosinase activity in hypothyroidism. Hypothyroidism is characterised by a decreased production of thyroid hormones which can have different symptoms, such as fatigue, cold intolerance, excessive sleepiness, increased cholesterol levels or in more severe cases slowing of the heart rate, drop in body temperature, and even heart failure. More recently, decreased carnosinase concentrations in the serum have been associated with Parkinson disease and total deficiency with neurological deficits [Wassif et al., 1994]. Most probably, carnosinase protects neuronal cells against oxidative stress and neuronal cells against ischemic injury [Schoen et al., 2003].
Ferene-S (3-(2-Pyridyl)-5,6-di(2-furyl)-1,2,4-triazine-5',5''-sulfonic acid) (P-8300) is a chromogen for serum iron determination [Charlier et al., 1992]. Compared to bathophenanthroline, which was used earlier, it is more sensitive and cheaper and it doesn't show interference with bilirubin, copper and haemoglobin.
4-Hydroxy-3-methoxymandelic acid (vanillylmandelic acid, VMA) (H-6500) is used as a standard in diagnostic tests. Measurement of VMA in urine is a necessity in patients with suspected neuroblastoma because urine VMA is elevated in 85 % of people with these tumors [Lee et al., 2003].
Inulin (I-6800) is a polysaccharide which naturally occurs in plants as energy reserve. In diagnostics, it is used to indicate problems or diseases of the kidneys by measuring the so-called glomular filtration rate (GFR). In the test, also known as inulin clearance, inulin is given through an intravenous infusion. Several times during the test, blood and urine are sampled and analysed. Inulin is only filtered, but not reabsorbed or secreted and can consequently be used to monitor the function of the kidneys [Price et al., 1974].
L-homocysteine (H-2800) is used as reference for measurement of L-homocysteine in plasma or serum for diagnosis of hyperhomocysteinemia or homocystinuria. Epidemiological studies have shown that hyperhomocysteinemia is related to a higher risk of coronary heart disease, stroke and peripheral vascular disease. Symptoms associated with homocystinuria may include mental retardation, psychiatric disturbances and abnormal thinning. Plasma homocysteine levels are strongly influenced by diet, as well as by genetic factors. Different methods of determining the plasma L-homocysteine are described by Frantzen et al. (1998) and Ueland et al. (1993).
Homovanillic acid (H-3200) is a major metabolite of catecholamine metabolism. An increased amount of homovanillic acid in the urine may be a sign of neuroblastoma. Homovanillic acid is also used as a reagent for the fluorimetric determination of oxidative enzymes such as peroxidase, glucose oxidase and xanthine oxidase [Guilbault et al., 1968]. Raje et al. (2002) showed that homovanillic acid can be used for the detection of sulfhydryl oxidase, an oxidase which occurs in a range of cellular locations and secretory fluids and has different putative roles.
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[2.] Frantzen, F.; Faaren, A.L.; Alfheim, I.; Nordhei, A.K. Clin. Chem. 1998, 44, 311-316.
Guilbault, G.G.; Brignac, P.J.; Zimmer, M. Anal. Chem. 1968, 40, 190-196.
Lee, K.L.; Ma, J.F.; Shortliffe, L.D. Urol. Clin. North AM 2003, 30, 881-890.
[3.] Price, M. Arch. Phys. Med. Rehabil.1974, 55, 522-523.
[4.] Raje, S.; Glynn, N.M.; Thorpe, C. Analytical Biochemistry 2002, 307, 266-272.
[5.] Schoen, P.; Everts, H.; de Boer, T.; van Oeveren, W. Clin. Chem. 2003, 49, 1930-1932.
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[7.] Ueland, P.M.; Refsum, H.; Stabler, S.P.; Malinow, M.R.; Andersson, A.; Allen, R.H. Clin. Chem. 1993, 39, 1764-1779.
[8.8] Wassif, W.S.; Sherwood, R.A.; Amir, A.; Idowu, B.; Summers, B.; Leigh, N.; Peters, T.J. Clin. Chim. Acta 1994 , 225, 57-64
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