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Creatinine is a product of muscle metabolism and generally excreted unchanged in urine via glomerular filtration. It is not reabsorbed at a significant amount through the kidneys. So, creatinine is a measure of renal function especially glomerular filtration and it is called glomerular filtration rate (GFR) (tubular secretion and tubular reabsorption don’t play much role here).
Significance of creatinine measurement: –
Kidney is an important organ to eliminate waste products from the body. Minerals such as sodium, potassium, chlorine and phosphorus are important to body but when they are higher than the certain level, kidney eliminates them through the urine. Same happens to creatinine. Extra creatinine gets eliminated daily through the urine.
Every day, 2% of body creatinine is converted to creatinine. Level of creatinine may vary from body mass, age, race and gender.
Moreover, kidneys also play an important role in creation of hormones, which are very important to regulate blood pressure and other body functions.
Below is the normal range of the substance in blood.
- Urea- 1.8-8.2 mmol/lit
- Phosphate- 0.8-8.4 mmol/lit
- Calcium- 2.0-2.6 mmol/lit
- Haemoglobin- 120-140g/lit (females) and 140-160 g/lit (males).
Thus, kidneys are vital organs of the body to keep one healthy and their dysfunction leads to severe problems.
Thus, it is important for one to keep kidneys healthy and Creatinine is an useful parameter of kidney function measurement.
Synthesis, Metabolism and Excretion: –
Anhydride form of creatine is called creatinine. The molecular weight of creatinine is 113 Da. Creatine is synthesized in the cells of liver, pancreas and kidneys. Primary source from which creatinine is created is amino acids: methionine, arginine and glycine in kidneys while in the liver, Methylation of the glyco cyamine by S- adenosylmethionine creates creatine. The cells in the muscle use this creatinine to produce creatinine phosphate. When muscle contracts, the phosphate from this creatine phosphate then transferred into ADP to make ATP and free creatinine is released. This creatinine is then transported to the kidneys to be excreted in urine via glomerular filtration. Thus, creatine phosphate is a good source of preserved energy and found everywhere but abundant in the retina, especially in the photoreceptor.
Transportation into the muscle depends on the concentration gradient and breakdown of creatine phosphate is stimulated by exercise. Creatinine and creatinine phosphate can be converted to creatinine nonenzymatically at the constant rate on daily bases. Daily creatinine turnover is 1.5% of the total body creatine.
Men have 0.6-1.2 mg/dl of creatinine while women have 0.5-1.1mg/dl. It is because men have more muscle mass than the women.
In premature neonates, the plasma concentration of creatinine is increases day by day and is observed to be highest on the third day the birth due to reabsorption.
Drugs such as Ketoacidosis, trimethoprim and cimetidine minimize the tubular secretion of creatinine and so enhance the accuracy of measurement of creatinine.
Antibiotics destroy the intestinal flora and interfere in creatinine excretion.
Generally, patients do not suffer from any significant renal function till the 30-40% of renal failure; thanks to good reserve capacity of the kidneys.
Below are the tests to estimate kidney function.
Generally, mild damage of kidney function cannot be tested through below tests as creatinine doesn’t alter to a significant amount until a severe kidney damage is detected.
For Uremic patients, creatinine test is not recommended as it doesn’t give an accurate result.
1. Creatinine clearance:
In this test, patient has to collect all the urine in one container over 24 hours.
The amount of creatinine is then measured through this sample collected over 24 hours.
2.0 mg/dl- Normal kidney function
1.6 mg/dl- significant renal damage
However, muscle mass is also taken into consideration to evaluate kidney disabilities.
This method is inconvenient and hence less preferred.
However, it is still used to diagnose few kidney conditions.
2. Glomerular filtration rate (GFR):
Blood creatinine is the efficient way to measure creatinine. It is called Glomerular filtration rate.
In this test, a patient has to give his/her blood sample and amount of creatinine is measured through this sample.
Isotope dilution mass spectrometry (IDMS) is used to measure serums creatinine. IDMA is the most effective technique now-a-days as it also diagnoses minute damage to the kidneys.
Below is the GFR level and associated Kidney Function (KF).
GFR- 90 or higher-Normal KF
GFR- 60-89- mild low KF
GFR- 45-59- moderate low KF
GFR- 30-44- moderate/severe decline in KF
GFR- 15-29- severe decline in KF
GFR- less than 15- kidney failure- requires dialysis.
Blood urea nitrogen (BUN) is another measure of kidney function. Urea level is accumulated if the kidneys are not functioning well. Blood urea nitrogen/ creatinine ratio is also a significant tool to estimate kidney function.
Other confirmation tests include albumin/ creatinine ratio (ACR). Normal albumin ratio in urine is lower than 30 mg/g. More than 30 mg/g is an indication of renal failure.
In neonates, creatinine measurement is interfered by bilirubin.
• Limit your exercise schedule- make your exercise routine at an optimum level.
• Limit high protein diet in case of high creatinine level.
• Increase protein-rich diet in case of low creatinine level.
• Limit sodium intake- high sodium leads to increase in blood pressure and so fluid retention which leads to high creatinine levels.
• Limit phosphorus intake- in case of high creatinine levels.
• Phosphorus-rich foods: cheese, fish, low-fat dairy products, pumpkins and soybeans.
• Limit potassium intake- in case of high creatinine levels.
• Potassium-rich foods: dried fruits, potatoes, spinach and bananas.