URIC ACID AND AMMONIA Flashcards
waste product normally formed in the body
major product of the catabolism of purine nucleosides:
adenosine & guanosine
Intermediate:
Xanthine
The bulk of purines ultimately excreted as uric acid in the urine arises from degradation of [?]
endogenous nucleic acids
released inside the body
endogenous
can be reused or recycled to form new nuceotides
purines
Reutilization of the major purine bases (?) is achieved through “salvage” pathways
adenine, hypoxanthine and guanine
[?] of the free bases causes re-synthesis of the respective nucleotide monophosphates
Phosphoribosylation
[?] - present as insoluble mosodium urate crystals
96.8% of uric acid in plasma
% is excreted through the urine
75%
Bacterial degradation in GIT:
allantoin and other compounds
RENAL HANDLING of URIC ACID
- Glomerular filtration
- Reabsorption at the pct
- Active secretion
- Reabsorption at the dct
Net excretion:
10%
FACTORS AFFECTING BUA LEVEL
- Diet: [?]
- Age & gender: increase w/ [?]; higher in [?] (gouty arthritis)
- 2x greater concentration in [?] than in plasma
- Avoid the use of [?] because it forms salts that cause turbidity
- UA is stable in [?] for several days at RT and longer at ref. temp.
- [/] increases its stability
legumes, seeds, internal organs
age; males
RBC
K oxalate
serum
Thymol
measures uric acid as an intact molecule
DIRECT METHOD: Phosphotungstic Acid (PTA)
- oxidizing agent
- reducing agent
Phosphotungstic Acid - oxidizing agent
Uric acid - reducing agent
degraded to form allantoin and CO2
DIRECT METHOD: Phosphotungstic Acid (PTA)
PTA is converted to tungsten blue (colorimetric)
DIRECT METHOD: Phosphotungstic Acid (PTA)
DIRECT METHOD: Phosphotungstic Acid (PTA) INTERFERENCES
1. Endogenous:
2. Exogenous:
glucose, ascorbic acid, glutathione, ergothionine cysteine (from hemolysis)
acetaminophen (paracetamol), aspirin (anti-cancer), gentisic acid, caffeine, theobromine, theophylline
The decrease in the UA concentration is determined by measuring the absorbance in the range of 290 – 300 nm (UV light)
A. Blaunch and Koch (UV test with uricase)
Trinder – Uricase method
Reduced chromogens:
DHBS: 3,5 – dichloro – 2- dihydroxy benzene sulfonic acid
PAP: 4 – aminophenazone
Trinder – Uricase method
Enzymes:
Oxidase or Uricase
Peroxidase
Trinder – Uricase method
End-product:
Quinoneimine (pink)
Uricase – catalase system
Formaldehyde + Acetyleacetone -
Formaldehyde + PAP -
yellow lutidine
trinder pink compound
Bittner method
Two sample measurements:
First:
Second:
treated with uricase to destroy uric acid
uricase is absent - Difference represents true UA
TPTZ Method by Morin
TPTZ :
2,4,6- tripyridyl – 5 – triazine
Amperometric Principle:
Polarographic method
HYPERURICEMIA Increased Formation Primary
- Idiopathic: unknown cause
- Inherited metabolic disorders: Lesch-Nyhan Syndrome
HYPERURICEMIA Increased Formation Secondary
- Excess dietary purine intake
- Increased nuclear breakdown (e.g. Leukemia high in lymphoblasts)
- Psoriasis
- Altered ATP metabolism
- Tissue hypoxia
- Pre-eclampsia
- Alcohol
HYPERURICEMIA Decreased Excretion Primary
- Idiopathic
HYPERURICEMIA Decreased Excretion Secondary
- Renal failure
- Drug therapy: salicylate/aspirin (promote circulation/prevent clotting)
- Poisons: heavy metal
- Pre-eclampsia
- Organicacids
- Trisomy21 (Down syndrome )
: x-linked genetic disorder (female carrier but does not express the trait – the male offspring will)
Lesch-Nyhan syndrome
deficiency of the enzyme, Hypoxanthineguaninephosphoribosyl transferase (muricase)
Lesch-Nyhan syndrome