Good ppt on serum uric acid

1. Estimation of serum uric acid

3. Salvage pathway

6. • Lower primates and mammals other than humans carry
purine metabolism one step further with the formation of
allantoin from uric acid, a step mediated by uricase.
• In humans, 75% of uric acid excreted is lost in urine,
remainder is secreted into GIT where it is degraded to
allantoin and other compounds by bacterial enzymes.
• The methods which are currently used to assay uric acid in
blood and urine depend upon either chemical or enzymatic
oxidation to allantoin.

7. Enzymatic method
(Uricase/Modified Trinder method)
Principle: Uricase converts uric acid to allantoin and
hydrogen peroxide. The hydrogen peroxide formed further
reacts with a phenolic compound and 4 aminoantipyrine by
the catalytic action of peroxidase to form a red coloured
quinoeimine dye complex. Intensity of the colour formed is
directly proportional to the amount of uric acid present in the
sample

8. Materials required
Reagent : 4-Aminoantipyrine
TBHB(2,4,6-Tribromo 3-hydroxy benzoic acid)
Uricase
Peroxidase
Tris buffer(pH – 8)
Uric acid standard- 8 mg/dL,
Serum sample,
Colorimeter,
Water bath- 37⁰C,
Micro pipette

10. • Mix well and incubate at 37* C for 5 min, read the
absorbance for the standard and test against blank at 520
nm
Addition
Sequence
B (ml) S (ml) T (ml)
Working Reagent 1.0 1.0 1.0
Distilled water 0.04 - -
Uric acid standard - 0.04 -
Sample - - 0.04

11. Mix well and incubate at 370 C for 5 min or at
R.T(250C) for 15 min. Measure the absorbance
at 520 nm for the standard (Abs.S) and test
sample(Abs.T) against the blank, within 30 min.
Calculations:

12. • Interfering substance: Hb and bilirubin
• Normal serum values
Serum - Females - 2.5- 5.6 mg/dl
Males - 3.1-7.0 mg/dl

13. Caraway’s method
Principle: Phosphotungstic acid in alkaline medium oxidizes
uric acid to allantoin and itself gets reduced to tungsten blue
which is measured colorimetrically at 670 nm

14. Caraway’s method

16. Hyperuricemia
> 7 mg/dl in males
> 6 mg/dl in females
1. Decreased excretion in urine : renal disorder
2. Increased production of uric acid:
a: Primary causes : HGPRT deficiency, PRPP synthetase
overactivity, G-6-Phosphatase deficiency
b: Secondary causes: Chronic lymphocytic leukemia,
Psoriasis, cancer chemotherapy etc
The secondary causes are more common than primary causes

18. Hypouricemia
< 2mg/dl
1. Enzyme deficiency: Xanthine oxidase
2. Decreased reabsorption in the kidney: Renal tubular
diseases like Fanconi’s syndrome
3. Decreased synthesis: Liver diseases
4. Drugs like 6-mercaptopurine inhibits de novo purine
synthesis leading to hypouricemia
Allopurinol

20. Gout
The accumulation of urate crystals in the synovial fluid resulting
in inflammation causing acute arthritis. Increased excretion of
uric acid may cause deposition of uric acid crystals in the
urinary tract leading to calculi or stone formation
Primary Gout: incidence is 1:500 in total population
1. Abnormal phosphoribosyl amidotransferase
2. Abnormal PRPP synthetase
3. Deficiency of enzymes of salvage pathway
4. Glucose-6-phosphatase deficiency

21. • Secondary Gout:
Increased urate production
Impaired urate excretion: 90% of hyperuricemias are due to
decreased renal clearance while 10% is due to increased
production:
• Rapidly growing malignant tissues, increased tissue damage due
to trauma and raised rate of catabolism as in starvation
• Reduced excretion : Renal failure

22. Alcoholism and gout

23. Pseudo Gout
• Due to accumulation of calcium pyrophosphate
dihydrate (CPPD) crystals. Knee joint is the most
commonly affected
• Excessive break down of ATP leads to increased
pyrophosphate which binds to calcium to produce
CPPD crystals