esp; to my supervisor dr.sahar iqbal my menotr .

1. Uric acid( urate)
Dr.Ghulam Murtaza
Resident Chemical Pathology
DIMC

2. Outlines:
Introduction
chemistry & physiology
Synthesis & salvage pathways
Renal excretion of uric acid
Clinical significance
Analytical methods

3. Biochem & Physiology
• In human it’s a major product of catabolism of
purine nucleoside ,adenosine & guanine .
• Purine from the catabolism of dietary nucleic acid is
is directly converted int uric acid
• Daily synthesis rate of uric acid is approx. 400mg ,
dietary source contribute another 300mg .

4. • In men ,consuming a free diet ,the total body
pool of uric acid is 1200mg ,& in women it is
estimated to 600mg
• By contrast Patient with Gouty arthritis, &
tissue deposit of uric acid pool may increase
up to 18000-30,000 mg .
• It is a weak organic acid that under physiologic
conditions exists mainly as a monosodium salt.

5. Synthesis
• First step is formation of 5” phosphoribosyl
amine
• Step is controlled by phosphoribosyl
pyrophosphate (PRPP)
• The first Purine nucleotide formed by ring
closure is INOSINE MONO PHOSPHATE ,
• ADENOSINE & GAUNOSINE are derived from
IMP.

7. Salvage pathways:
• Reutilization of major purine bases like Adenine
,Guanine ,& hypoxanthine .
• In which phosphorribolysation of the free bases
leads to resynthesis of the respective nucleotide
mono phosphate
• Adenine is converted into converted into
adenosine mono phosphate thru the action of
(APRT) adenosine phosphoribosyl transferase .

9. Renal excretion of uric acid
occurs in 4
steps :
Glomeruli
filtration of
virtually all
the uric
acid
entering in
capillary
plasma
entering
the
glomerulus.
Reabsorpti
on-in PCT
of about
98-100% of
filtered uric
acid
Subsequent
secretion of
uric acid
into DCT.
Reabsorpti
on in the
distal in the
distal
tubules
Net urinary
excretion of
uric acid is
6%-12% of
the amount
filtered

11. • Uric acid is dibasic ,having two pka
first pka value is 5.75 ,above this pH uric acid
exits chiefly as URATE ION .is more soluble
than uric acid, In kidney tubules mostly.
• 2nd pka In blood ph. above 5.75 it exits in
monosodium urate ,ten time more soluble
than uric acid

12. Clinical significance
• two most common clinical use for urate is Gout &
determination of therapy adequacy .
• Hyperuricemia :
. Increased serum uric acid levels above 7 mg/dl in Men &
above 6 mg/dl in women.
Classification of hyperuricemia
Serum uric acid.
24 hours urine uric acid
Over
Production
Under excretion
Serum uric
acid
high high
Urine uric
acid
high Normal /low

13. Hyperuricemia

14. Gout :
• Is a metabolic disorder of purine catabolism, resulting in
overproduction of uric acid so deposition of Monosodium urate
crystals (MSU ) occurs .
• Classification of gout :
Primary gout
Secondary gout
• Primary gout :
due inborn defect in purine metabolism or inherited defects in
renal tubular secretion of urate .
• Secondary gout :
attributed to several identifiable causes like
CKD,DM,DKA,Diuretics ,& Lactoacidosis

15. Stages of classic Gout

18. Hypouricemia
Serum urate concentration less than 2.0mg/dl
Less common than hyperuricemia
Causes :
Severe hepatocellular with reduced purine synthesis or xanthine oxidase
Defective Renal tubular reabsorption of uric acid
Congenital defect like Fanconi syndrome
Overtreatment of uricosuric drugs & chemotherapy with azathioprine

19. Kidney stones
Uric acid kidney stones occurs in approx.
one in five patient with clinical gout
Formed in acidic pH
(pka 5.57 ) uric acid becomes insoluble
Patient having persistently pH less than 6, having normal
urinary concentration of uric will produce supersaturation .
Allopurinol is
mainstay of treatment

20. Analytical Method
Phosphotungestic acid(PTA) ,HPLC , & Uricase method are used .
The enzyme uricase is a oxidoreductase .
Main sources are aspergillus flavus ,candida utilis ,hog liver & bacillus fastidious
Uricase method is popular ,feasible, low cost preparation & easily availability
Most commonly used method world wide now a days

21. Principles of the procedure
The uric acid is converted by uricase to allontoin & hydrogen
peroxide .
Formed hydrogen peroxide further react with
phenolic compound & 4-AAP by catalytic action of peroxidase to
form a PINK colored quinone diamine dye complex .
The level of resulting complex is directly proportional to uric acid
level of sample

23. In our lab
Uricase method is bieng use .

24. Reference intervals
• Increase gradually with age 20-60 about 10 % .
• Pregnancy .
• In normal level
• In urine
32 weeks 36 weeks 38 weeks
1.9-5-5 mg/dl 2.0- 5.8 2.7- 6.5 mg/dl
Men Women
3.5 – 7.2 mg/dl 2.6- 6.0 mg/dl
Diet containing purines Purines free diet
250mg/dl – 750mg /dl Less than 400 mg/dl

25. • Reference
• Tietz 6th edition volume 1st
• Chemical pathology for beginners
( Dr .Amir Ijaz )

26. • Thank you