Examinations
Examinations
All human blood passes through the kidneys about 100 times per day. The liquid portion of the blood is filtered through small units (nephrons), after which most of the liquid is reabsorbed back into the bloodstream. Liquid waste not reabsorbed by the kidneys is excreted from the body with urine.
Creatinine (from the Greek kreas — "meat") is a product of creatine phosphate breakdown in muscle tissue. Its amount in the body is relatively constant and depends on the individual's muscle mass. Chemically, creatinine is a cyclic derivative of creatine.
Creatinine is filtered out of the blood by the kidneys and excreted in small amounts with urine. Tubular reabsorption of creatinine is minimal. If the kidneys' filtration capacity is impaired, blood creatinine levels rise. By knowing creatinine levels in both blood and urine, it is possible to calculate creatinine clearance, which reflects the glomerular filtration rate (GFR).
Creatinine clearance (from "clearance," meaning the removal or elimination of creatinine) indicates the amount of blood that the kidneys can clear of creatinine in one minute. In healthy individuals, this is approximately 125 ml/min, meaning the kidneys clear 125 ml of blood of creatinine every minute.
GFR represents the sum of filtration rates of all functioning nephrons in the kidneys. This measure is critical for assessing the number of functioning nephrons in the kidneys and is a vital indicator of kidney health.
Creatinine clearance increases in severe kidney dysfunction, as creatinine is eliminated more actively through secretion.
Creatinine clearance can be measured in two ways:
- By determining the amount of creatinine in a person’s blood and their 24-hour urine collection.
- More commonly, via a blood test, which is more convenient for the patient.
Regular determination of creatinine clearance allows doctors to monitor changes in kidney function over time and adjust treatment accordingly.
- Avoid alcohol for 24 hours before the test.
- Refrain from eating for 12 hours prior to the test.
- Do not take diuretics for 48 hours before urine collection (consult your doctor beforehand).
- Avoid physical and emotional stress for 24 hours before the test.
- Do not smoke for 30 minutes before the test.
- Assess kidney function.
- Monitor the progression of kidney diseases.
- Evaluate kidney function in patients receiving nephrotoxic drugs.
- Determine severe dehydration.
- Kidney pain.
- Swelling around the eyes or ankles.
- High blood pressure.
- Low urine output or urination problems.
- Dark urine or blood in the urine.
Conditions include:
- Alport syndrome.
- Amyloidosis.
- Chronic kidney disease.
- Cushing's syndrome.
- Dermatomyositis.
- Diabetes mellitus.
- Poisoning by cardiac glycosides.
- Generalized tonic-clonic seizures.
- Goodpasture syndrome.
- Hemolytic-uremic syndrome.
- Hepatorenal syndrome.
- Interstitial nephritis.
- Lupus nephritis.
- Malignant hypertension.
- Membranoproliferative glomerulonephritis.
Causes of Reduced Creatinine Clearance:
- Acute kidney failure.
- Blockage of urine flow at the bladder outlet.
- Chronic heart failure.
- Dehydration.
- Chronic kidney disease.
- Glomerulonephritis.
- Shock.
Causes of Elevated Creatinine Clearance:
- Pregnancy.
- Diabetes (before the onset of diabetic nephropathy).
- High dietary protein intake.