Estimation of creatinine in serum - Kidney function tests

    Kidney function tests (KFT)
    Estimation of creatinine in serum
    • 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


    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


    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 37 , then add 100 µ serum that incubated also for 5 min at 37 then mix well and read


    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 knownCreatinine clearance



    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


    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
    GFR


    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

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