1. Measurement of Serum Uric Acid Illustration for Practical lessons; 2 nd. Year medical students, Mosul Medical College, 2013 Dr. Amjad Hazim Abid Al-Naemi Lecturer/ Dept of Biochemistry/ Mosul Medical College

2. In human kind, uric acid (urate) is the end product of purines (hypoxanthine, adenine and guanine) degradation.. liverintestine It is produced mainly in those tissues containing the highest activity of the enzyme “xanthine oxidase”- mainly the liver and the intestine. In the blood, it is present as monosodium, potassium, ammoniumm or other salts. However, monosodium urate is the most abundant.

4. Sources Exogenous: Ingested nucleoproteins (diet) Endogenous: -Degradation of endogenous Nucleoproteins (e.g muscle proteins) - Degradation of cellular nuclear materials due to cell turnover (all types of cells)

5. Body Content & Dynamics  Total uric acid content in adult humans’ body is around 1.1 gm  50% of this content is being eliminated and replaced daily  It is mainly excreted through kidneys  Little amount only is excreted through intestine

6. RENAL HANDLING Freely filtered by renal glomeruli (ultra filtration). About 98-100% of the filtered urate in the glomeruli will be reabsorbed in the renal PCT. However, around half of the reabsorbed amount will be secreted again. After secretion in the tubules, around 60-70% of urate will be reabsorbed back again to the blood and finally around 10-12% of the initial filtrate will be excreted in the urine.

7. Reference values -Children: 3-4 mg% (180- 240 μmol/l) -Adult males & post-menopausal women: 3.5- 7.0 mg% (210- 420 μmol/l) -Adult pre-menopausal females: 2.5- 6.0 mg% (156- 360 μmol/l)

8. Do you know any biological function for uric acid in human body?

9. Hyperuricaemia Serum uric acid˃ 7.0 mg% (420 μmol/l) in adults. Notice: The plasma is saturated with uric acid depending on many factors (like pH and urate concentration) and the urate is soluble. However, above the concentration of 6.8- 7 mg% (408- 420 μmol/l), the supersaturation takes place and the urate starts to precepitate as crystals in body tissues (mainly joints, peri-articular soft tissues and kidneys) causing problems.

10. Causes of Hyperuricaemia In general, hyperuricaemia can be classified into three categories according to its aetiology:  Hyperuricaemia due to overproduction of urate  Hyperuricaemia due to underexcretion  Hyperuricaemia due to both However, the most common cause is defective renal excretion although the causes in general will include the following:

11. 1.Excessive dietary intake of nucleoproteins 2.Essential (primary) hyperuricaemia (Gout) 3.Increased nucleic acid turnover; myeloproliferative disorders (eg. Leukaemias), lymphoproliferative disorders (e.g lymphoma), polycythemias, hemolytic anaemia, treatment with cytotoxic drugs.

12. 4. Impaired renal excretion; renal insufficiency, drug therapy like diuretics and alcoholism and in ketoacidosis (severe uncontrolled diabetes mellitus), lactic acidosis. 5.Specific enzyme defects (genetic disorders of enzymes involved in purines metabolism); eg. ↓ HGPRT (as in Lesh-Nyhan syndrome); decrease salvage of hypoxanthine and guanine with increased availability of PRPP and increases purine production and PRPP synthetase 6. Hypertension 7. Diabetes mellitus 8. Obesity 9. Glucose 6- phosphatase deficiency (Von Gierke disease) 10. Fructose intolerance 11. others

13. Clinical Presentation Uric acid crystals would precipitate in the joints and peri- articular soft tissues (producing gouty arthritis) and in the kidneys producing urate stones (urolithiasis). Gout: It is a disorder of joints and soft tissues characterized by high levels of uric acid in blood (hyperuricemia), either due to overproduction or underexcretion of uric acid.

14. The precipitation of monosodium urate crystals in the joints, and the inflammatory response to the crystals, cause first acute and then chronic gouty arthritis. Nodular masses of monosodium urate crystals (tophi) may be deposited in the soft tissues, resulting in chronic tophaceous gout.

15. Lesch-Nyhan syndrome is an X-linked, recessive inherited disorder that is associated with a virtually complete deficiency of HGPRT This deficiency results in an inability to salvage hypoxanthine or guanine, from which excessive amounts of uric acid are produced. In addition, the lack of this salvage pathway causes increased PRPP levels and decreased IMP and GMP levels.

16. In patients with Lesch-Nyhan syndrome, the hyperuricemia frequently results in the formation of uric acid stones in the kidneys and the deposition of urate crystals in the joints (gouty arthritis) and soft tissues. In addition, the syndrome is characterized by:  motor dysfunction,  cognitive deficits, and  behavioral disturbances that include self- mutilation (biting of lips and fingers).

17. Principle of Lab Measurement using manual kit from “Rrandox” Uric Acid is transformed (oxidized) by uricase to allantoin and hydrogen peroxide (H2O2), which under the catalytic influence of peroxidase (POD), reacts with 4- aminoantipyrine and 3- hydroxy-2,4,6 triiodobenzoic acid to produce a colored complex (light pink ) whose color intensity is directly proportional to the uric acid conc. in the sample.

18. Procedure -In a clean test tube labeled as “T”; add 1 ml of working reagent and add 20 μl of serum -In a clean test tube labeled as “Std”; add 1 ml of working reagent and add 20 μl of standard uric acid solution (conc.= 5.7 mg%) -Incubate the tubes at 37C˚ for 5 min -Read absorbance of T and Std against blank at 510 nm Note: the blank in this case is just the working reagent± DW

19. Calculation S.[uric acid] in mg%= A t/A std x conc. of Std = A t/A Std x 5.7 Conversion from conventional (mg%) to SI unit (μmol/l) is by multiplication with 59.7 (or roughly 60)