5. • A proportion of the free
creatine in muscle
spontaneously and irreversibly
converts to its anhydride waste
product—creatinine.
• Thus the amount of creatinine
produced each day is relatively
constant and is related to the
muscle mass.
• In health, the concentration of creatinine in
the bloodstream is a so relatively constant,
although dietary meat intake may influence
the value. Creatinine is present in a body
fluids and secretions and is freely filtered by
the glomerulus. Although it is not
reabsorbed to any great extent by the renal
tubules, a small but significant tubular
secretion occurs
5
6. Clinical significance
• Serum creatinine concentration is maintained within narrow limits
predominantly by glomerular filtration. Consequently, both serum
creatinine concentration and its renal clearance (“creatinine clearance”)
have been used as markers o the glomerular filtration rate (GFR)
6
7. Analytical Methodology
• enzymatic methods
• Chemical methods: the Jaffe Reaction
• Isotope dilution mass spectrometry (IDMS)
• high-performance liquid chromatography (HPLC)
7
9. Problems of
The Jaffe Reaction
Lack of specificity for creatinine: many compounds have been reported to
produce a Jaffe- like chromogen:
(1) ascorbic acid, (2) blood-substitute products*, (3) cephalosporins, (4)
glucose, (5) guanidine, (6) ketone bodies, (7) protein, and (8) pyruvate
9*A blood substitute (also called artificial blood or blood surrogate) is a substance used to mimic and fulfill some functions of
biological blood
11. Creatininase
creatinin creatine
detected with a series of enzyme-mediated reactions
involving (1) creatine kinase, (2) pyruvate kinase, and (3)
lactate dehydrogenase, with monitoring of the decrease in
absorbance at 340 nm
11
13. Creatininase and Creatinase
Inclusion of ascorbate oxidase Overcome potential ascorbic acid interference
Potassium ferricyanide Minimize of bilirubin interference
Bilirubin oxidase
The influence of endogenous intermediate creatine and urea has been minimized by adding
a preincubation step and then initiating the reaction with creatininase.This system has been
incorporated in a point-of -care testing device using polarographic detection.
An alternative detection system involves measurement of the reduction of nicotinamide
adenine dinucleotide by formaldehyde in the presence of formaldehyde dehydrogenase.
13
15. Creatinine Deaminase
• Creatinine deaminase catalyzes the conversion of creatinine to N-methy
hydantoin and ammonia. Early methods concentrated on the detection of
ammonia using glutamate dehydrogenase or the Berthelot reaction. An
alternative approach involves the enzyme N-methylhydantoin
amidohydrolase.
15
19. Clinical Significance
• Creatinine measurement is better than urea
• Serum and urinary urea measurement, however, may still provide useful
clinical information in particular circumstances, and measurement o f urea
in dialysis fluids is widely used to assess the adequacy of renal replacement
therapy
19
21. Chemical methods
• Most chemical methods for urea are based on the Fearon reaction, in which
molecules of diacetyl condense with those of urea to form the chromogen
diazine, which absorbs strongly at 540 nm.
21
24. Biochemistry and Physiology
• In humans, uric acid is the major product of catabolism of the purine
nucleosides adenosine and guanosine
24
25. Clinical Significance
• Kidney failure or stones in a child or young adult
• Gravel in infant’s diaper
• Unexplained neurological problems in an infant, child or adolescent
• Gout
25
27. • Kidney disease associated with hyperuricemia may take one or more o
several forms: (1) gouty nephropathy with urate deposition in renal
parenchyma, (2) acute intratubular deposition of urate crystals, and (3)
urate nephrolithiasis.
27
30. Secondary gout
Renal retention of uric acid Renal diseases
Administration of drugs
especially diuretics
Organic acidemia
Increased nucleic acid turnover
rapid proliferation of tumor cells and in massive
destruction of tumor cells when therapy with
certain chemotherapeutic agents is provided.
30
32. Phosphotungstic Acid Methods
PTA Urate
Alkaline mediume
Blue Chromogen
Are subject to many interferences, and
efforts to modify them have little success in
improving their specificity 32
