Kidney function tests (KFT)
![Estimation of creatinine in serum]( "Kidney function tests")
- It is a collective term for a variety of tests that can be done to evaluate how well kidneys are functioning
- Many conditions can affect the ability of kidneys to carry out their vital functions , some lead to rapid decline(acute) in kidney functions and others lead to gradual decline(chronic)in function
- Both chronic and acute result in a buildup of toxic waste substances in the blood
Kidney function tests as:
- Creatinine
- Urea
- Blood urea nitrogen (BUN)
- Uric acid
- Levels of other elements regulated by kidney as : sodium, potassium ,chloride ,calcium ,magnesium ,phosphorus
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Estimation of creatinine in serum
Introduction
- Creatinine is a chemical waste product that is generated from muscle metabolism
- Creatinine is produced from creatine ,a molecule of major importance for energy production in muscles
- Creatinine is transported through blood stream to the kidneys , the kidney filter out most of creatinine blood and dispose it in the urine
- A high blood level of creatinine indicates that the kidneys may not be working properly
- Creatinine is usually more accurate marker of kidney function than urea
Principle
- Creatinine in alkaline medium reacts with picric acid to form a yellowish red complex of creatinine picrate
- The intensity of color is measured at 520 nm
- The rate of formation of color is proportional to the creatinine in the sample
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Normal range
- In adult male : 0.6 – 1.2 mg %
- In adult female : 0.5 – 1.1 mg %
- Note : females have a lower creatinine than males because they have less muscle mass
Reagents
- R1 : Alkaline buffer
- R2 : Picric acid
Procedure
- Depend on a kinetic technique
- Add 500µ R1 + 500 µ R2 incubate for 5 min at 37ᵒ , then add 100 µ serum that incubated also for 5 min
at 37ᵒ then mix well and read
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Serum creatinine levels are increased in:
- The most common causes of chronic kidney disease in adults are high blood pressure and diabetes mellitus
- Damage or swelling of blood vessels in kidney caused by infection or autoimmune diseases and prostate diseases
- Bacterial infections of the kidney
- Kidney stones or other causes of urinary tract obstruction
- Acute tubular necrosis (death of cells in the kidneys’ tubes) caused by drugs or toxins
Serum creatinine levels are decreased in:
- Mean lower muscle mass or muscle disease
- Pregnancy can also cause low blood creatinine levels
- Liver disease which affect creatine production which can cause low creatinine
Creatinine clearance
- Creatinine clearance test measures creatinine levels in both a sample of blood and a sample of urine from a 24 hour urine collection
- The results are used to calculate the amount of creatinine that has been cleared from the blood and passed into urine
- The amount of creatinine produced in the body depend on muscle mass and is relatively constant for an individual
- The amount of creatinine removed from the blood depend on both the filtering ability of the kidneys and the rate at which blood is carried to the kidneys
- There are several versions of the creatinine clearance calculation , all of them include the measurement of the amount of creatinine in a blood sample collected just before or after the urine collection , the amount of creatinine in urine sample and the 24 hour urine volume
- Creatinine clearance gives better information than the blood creatinine test on how well the kidneys are working
- It can be calculated if values of creatinine urine concentration
, urine flow rate and creatinine serum concentration are known
![Creatinine clearance]( "Creatinine clearance")
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Normal range
- In males : 90 – 140 ml/min
- In females : 87 – 170 ml/min
Creatinine clearance levels increased in:
- Excessive exercise
- Muscle injury
- Carbon monoxide poisoning
- Commonly seen during pregnancy
- In patients with diabetes
- Occur with large dietary protein intake
Creatinine clearance levels decreased in:
- Serious kidney damage that result from:
- Urinary tract blockage or low blood flow to the kidneys
- Infection
- Cancer
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Glomerular filtration rate (GFR)
- GFR is a test used to check how well the kidneys are working specially , it estimates how much blood passes through the glomeruli each minute (glomeruli are the tiny filters in the kidney that filter waste from the blood)
- GFR can be calculated by combining the creatinine level in blood and some factors as : age , blood creatinine , height , weight , gender , ethnicity
- GFR decrease with age
Normal range
- GFR values can be classified as follows:
- Normal : 100 – 140 ml/min
- Mild kidney failure : < 90 ml/min
- Moderate kidney failure : <60 ml/min
- Severe kidney failure : < 30 ml/min
- End- stage kidney failure : < 15 ml/min which is incompatible with life , without dialysis or transplantation