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Overview :
The rate of creatinine production is
• proportional to body weight;
• decreases with age;
• is slower in females than in males.
Factors affecting creatinine clearance:
1) sex: It
is normally less in women than men.
2) age:
(2a) It is
lower in children, until the age of 2.
(2b) It
usually decreases in adults with age, starting at age 20.
3) muscle
mass: This is the reason for decrease seen in elderly. It can also be important
in patients with myopathies and patient with cachexia.
4)
pregnancy
5)
hyperglycemia: Due to osmotic diuresis and body fluid redistribution.
6) patients
with morbid obesity or marked ascites: They excrete less creatinine per kg than
expected; you need to correct to lean body weight if these are marked.
7)
proteinuria: This results in increased creatinine clearance.
8) time of
day: It is highest in afternoon.
Accuracy of creatinine clearance based on 24-hour urine
collection is dependent on how well the patient follows instructions and upon
preservation of the specimen.
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