Serum Creatinine test
• Creatinine is a waste product, anhydride form of creatine and creatine
phosphate.
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CH3
CH3
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│
│
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H2C ------ N
H2C ------ N
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│
│
│
│
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0═C
C ═ NH
C ═ NH
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│
│
│
│
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OH NH2
O ═ C --------N
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│
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H
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Creatine
Creatinine
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Creatine is synthesized in the liver and pancreas from three amino
acids: arginine, glycine, and methionine. After synthesis, creatine
diffuses into the vascular system and is supplied to many kinds of cells,
particularly the muscle, where it is phosphorylated by ATP to creatine
phosphate.
● Creatine and creatine phosphate total approximately 400 mg/ 100g of muscle.
● Creatine is filtered by glomeruli but is largely reabsorbed at the
proximal tubule: hence there is very little excretion of creatine in the urine.
● Both creatine and creatine phosphate are spontaneously converted
largely in muscles into creatinine at a rate of approximately 2% per day
by irreversible nonenzymatic removal of water.
● The body content of creatine is proportional to muscle mass; therefore,
the level of creatinine in the body is also proportional to muscle mass;
● Creatinine is removed from the plasma by glomerular filteration. No
reabsorption of creatinine occurs in the renal tubules; i.e. creatinine has
high clearance rate as compared to urea.
Clinical Significance
• Serum creatinine determination is significantly more reliable than plasma urea
determination since it is not affected by dietary protein.
• Because kidney can also secrete creatinine through the tubules, blood creatinine
levels in renal disease do not increase untile kidney function is severely impaired
(~50% of function test).
• Increase in creatinine above 2-4 mg/dl is suggestive of moderate to severe kidney
damage.
• Minor changes in blood creatinine concentration may be of significant and indicate
impairment of renal function.
• ● Simultaneous determination of urea and creatinine is of value in the differential
diagnosis of prerenal, renal, and postrenal hyperuremia.
• ■ Normal rate of urea/creatinie is between 15/1 to 24/1.
urea/creatinie ratio
-INCREASED UREA:CREATININE RATIO
dehydration/prerenal failure
corticosteroids
haemorrhage
protein-rich diet
severe catabolic state
-DECREASED UREA:CREATININE RATIO
severe liver dysfunction
intrinsic renal damage
malnutrition
pregnancy
low protein diet
Creatinine clearance Tests
The creatinine clearance is a very sensitive indicator of glomerular filtration rate
(GFR).
The creatinine clearance test helps provide information about how well the kidneys
are working. The test compares the creatinine level in urine with the creatinine
level in blood.
How the Test is Performed
This test requires both a urine sample and blood sample. You will collect your urine
for 24 hours and then have blood taken.
• The creatinine clearance (CrCl ) is calculated from the following formula:
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Urine Volume
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CrCl (ml / min) = ---------------------------•
S.Cr*24*60
• 24 hours
• 60 second (1minute)
Normal range(CrCl)
Male 90-140ml/minute
Female 80-125 ml/minute
Increased serum creatinine:
-Doing strenuous exercise two days before testing •
-Eating high amounts of meat (eight ounces) within 24 hours of testing
-Impaired renal function
– Vary large muscle mass: body builders, giants, acromegaly patients
– Athletes taking oral creatine
– Drugs:
• Probenecid
• Cimetidine
• Triamterene
• Trimethoprim
• Amiloride
•
When you do S.Creatinine?
doctor may order a creatinine blood test to assess the •
creatinine levels if there are signs of kidney disease. These
symptoms include:
trouble sleeping •
a loss of appetite •
lower back pain near the kidneys •
changes in urine output and frequency •
high blood pressure •
nausea •
vomiting •
Normal range
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Male:
0.6 -1.4 mg/dl (53- 93 µmol/l)
Female:
0.5- 0.9 mg/dl (44- 80 µmol/l))
Urine 24hrs Male 1.0 – 2.0 g/day
Female 0.8 – 1.8 g/day
Specimen
-One can analyze serum, plasma, or diluted urine(1:100).
-The common anticoagulants (fluoride and heparin) do not
cause interference,.
-Storage
7 days at 4-25oC
At least 3 months at -20oC
Interferences
1- Hemolysis, bilirubin may cause falsely results.
2- Ascorbic acid, and some antibiotics interfere also with the
determination of creatinine according to Jaffe method
Methods for creatinine determination
The methods used to measure creatinine are based on the Jaffe reaction:
•Kinetic method
•Enzymatic method
Determination of creatinine by kinetic method
Principle
Creatinine reacts with picric acid under alkaline condition to form a
yellow complex. The absorbance of the color produced,
measured at a wavelength 492 nm, is directly proportional to
creatinine concentration in the sample..
Creatinine + picric acid
Alkaline pH yellow complex
Serum creatinine procedure
• Procedure
Standerd
1ml
Sample
1 ml
Working reagent
(0.5ml R1+0.5ml R2)
Distilled water
-----------Standard
100 µl
-----Sample
------100 µl
• Mix well. After 30 seconds, record absorbance A1 at 490 nm
against reagent blank or distilled water. Exactly 2 minutes
after the first reading, record absorbance A2.
Calculation
A2-A1 = ∆Asample or ∆Astandard
∆Asample
--------------------- × standard conc. = Conc. Of creatinine (mg/dl or µmol/l)
∆Astandard
Home work
A 19-year-old woman is hospitalized for acute kidney injury (AKI) associated with
bloody diarrhea that developed after she returned from a trip to South America. She
also has nausea, vomiting, abdominal pain, fever, chills, and decreased urine
output. Medical history is otherwise unremarkable, and she takes no medications.
On physical examination, temperature is 37.8°C (100.0°F), blood pressure is
135/90 mm Hg, and pulse rate is 110/min. The oral mucosa is dry. There is diffuse
abdominal pain with guarding. The remainder of the physical examination is normal.
Laboratory studies show haptoglobin 8 mg/dL (80 mg/L), hemoglobin 5.2 g/dL (52
g/L), leukocyte count 20,000/µL (20 × 109/L), platelet count 36,000/µL (36 × 109/L),
reticulocyte count 7.8%, serum creatinine 5.7 mg/dL (504 µmol/L) and lactate
dehydrogenase 2396 units/L. Peripheral blood smear showed many schistocytes
and urinalysis many erythrocytes and erythrocyte casts. Urine protein creatinine
ratio is 0.5 mg/mg.
Which of the following is the most likely cause of this patient's acute kidney
injury?
A. Acute tubular necrosis
B.. Hemolytic uremic syndrome
C. Postinfectious glomerulonephritis
D. Scleroderma renal crisis