1. Uric acid test By 51 Fifth Stage Student Sakar Karem Abdulla
M.Sc. Clinical Biochemistry

2. Urate Urate is the end product of purine metabolism.
Purines (adenine,guanine) are constituent of nucleic acid DNA and RNA.
Purine in the body may be derived from the breakdown of ingested nucleic acid, or may be from breakdown of endogenous nucleic acid or may be synthesized de novo.
In humans there is lack of uricase which convert uric acid to more water soluble allantoin.

3. Breakdown of ingested nucleic acid

4. Breakdown of endogenous nucleic acid

5. Purine synthesis

6. Fate of purines
Purines oxidized to urate:  adenine is oxidized to hypoxanthine then to xanthine. Guanine can also form xanthine. Xanthine, in turn, is oxidized to form urate.
Purines reused for nucleic acid synthesis: xanthine, hypoxanthine and guanine can be resynthesized to purine nucleotides by pathways involving hypoxanthine-guanine phosphoribosyl transferase (HGPRT) and adenine phosphoribosyl transferase (APRT).

7. Excretion of urate
Via the kidney: Seventy-five percent of urate is excreted via the kidney. Urinary excretion in male lower than female which contribute to higher incidence of hyperuricaemia in men.
Via the gut: the remaining 25 percent of urate are excreted into the gut where it is broken down by bacteria this process is called uricolysis.
The amount of urate excreted in the urine is around 10% of that filtered at the glomerulus

8. Hyperuricaemia
This is increase in blood levels of uric acid that is greater than 7mg/dl in men and more than 6mg/dl in women.
Hyperuricaemia can occur by two mechanisms:
Increased production (overproducers)
Decreased excretion (underexcretors)

9. Overproduction of uric acid
Increased purine synthesis related to genetic disorder (primary hyperuricaemia):
Purine synthesis is increased due to over activity of amidophosphoribosyl transferase, which controls the formation of phosphoribosylamine.
In Lesch-Nyhan syndrome Purine synthesis is increased caused by a reduced activity of HGPRT.
In von gierke disease due to deficiency of glucose-6-phosphatase

11. Overproduction of uric acid
Increased turnover of nucleic acid (secondary hyperuricaemia):
In rapidly growing malignant tissue
In psoriasis
After the treatment of large malignant tumors by radiotherapy or cytotoxic drugs (tumour lysis syndrome)
During starvation

12. Under excretion of uric acid
Reduced excretion of urate may related to:
Renal glomerular dysfunction
Metabolic acidosis
Certain drug: thiazide diuretic

13. Factors contributing to hyperuricaemia
A high-meat diet
Alcohol
Obesity
plasma uric acid in male more than female and in female in post-menopausal more prone then pre-menopause.

14. Consequences of hyperuricaemia
precipitation of urate in kidneys and renal calculi which causing progressive renal damage.
Precipitation in joints especially those of feed produces the gout.
Precipitation also may occur in subcutaneous tissues especially of the ears and tendons this called gouty tophi.

15. Aim of Uric acid test Diagnose gout
Monitor uric acid levels in patients undergoing chemotherapy or radiotherapy
Monitor the efficacy of treatment given to lower uric acid levels
To assess the risk and cause of recurrent kidney stones

16. Investigation of hyperuricaemia

17. Reagents of the test
Reagent 1 buffer solution: phosphate buffer, 2-4 DHBS
Reagent 2 enzyme: uricase, peroxidase, 4-aminophenazone
Reagent 3 standard: uric acid 6 mg/dl

18. Principle of the test Enzymatic and colorimetric method
Uric acid+ 2H2O + O2 → Allantoin+ CO2 + H2O (by uricase)
2H2O2 + 4-Aminophenazone + 2-4Dichloro-phenol-sulfonate→ Quinoneimine+4H2O
(by peroxydase)

19. Procedure for S.Uric acid

20. Calculation Normal range: 2.5-6 mg/dl (women)
S.Uric acid=Abs.Assay/Abs.standard  x conc.standard (6 mg/dl).
Normal range: mg/dl (women)
3.5-7 mg/dl (men)