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How to read your medical test report: Kidney function test

All you need to know about reading your kidney function test report.

Kidneys regulate urinary system and filter out toxins from the body. They control water and mineral levels and help maintain blood pressure and acid- base levels in the body. An infection, diabetes, hypertension, high cholesterol levels, autoimmune disorders, habitual pill-popping or physical damage can cause kidney dysfunction. Kidney disease is no more a disease of the elderly. Sedentary lifestyle and addiction to smoking and liquor are taking a toll on the kidneys of the youth.

Kidney function tests what are they?

Several markers in the blood and urine can help identify kidney function. Urea and creatinine are the gold standard markers to detect kidney disease. Kidney function tests are simple blood and urine tests that check whether your kidneys are working properly by measuring the levels of markers. They help identify problems with the functioning of your kidneys. Various kidney function tests are:

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1. Blood creatinine test: Creatinine is a waste product produced by your muscles. It is entirely filtered from the blood by the kidneys and excreted in the urine. A blood creatinine test measures the amount of creatinine in your blood. How to read your medical reports: Complete Blood Count

2. Blood urea nitrogen (BUN) test: Urea is a waste product produced by the breakdown of proteins. It is filtered by the kidneys and excreted in the urine. BUN test measures the amount of urea nitrogen in your blood. How to read your medical test report: Blood culture test

3. Urinalysis: Analysis of the urine sample is used to detect the presence of protein and blood cells (RBCs and WBCs) in your urine.

4. Urea clearance test: The test measures the volume of plasma from which urea is completely cleared by the kidney in a minute. This test is based on a comparing the amount of urea in the blood with urea in the urine.

5. Creatinine clearance test: The test determines the rate at which the kidneys are filtering creatinine. It compares the amount of creatinine in blood with creatinine in urine.

6. Glomerular filtration rate (GFR): Glomerular filtration rate is the rate at which fluid is filtered through your kidneys. It is determined by measuring the clearance of an ideal marker. Estimated GFR (eGFR) is an approximated value that is derived from a formula based on your blood creatinine level, age and gender. How to read your medical test report: Blood glucose tests

When are the tests recommended?

The filtration capacity of kidneys naturally declines after the age of 30. Kidney disease usually goes unnoticed until there is significant damage to the kidney function. Hence assessment of kidney function is recommended after you cross your 50s.

Diabetes and high blood pressure are the leading causes of kidney disease and kidney failure. Hence, regular screening of your kidney function is advised if you have these health conditions.

Reading your kidney function test report

The values of different blood and urine markers may help assess your kidney function. The ratio of their values can give the actual rate of clearance of your kidneys. Different reference ranges may be used by different labs. Normal ranges may vary with age too. You can follow a few tips to prevent kidney problems.

1. Blood creatinine levels

Normal range: Males - 0.8 to 1.2mg/dL and Females - 0.6 to 0.9mg/dL

A higher level may indicate that your kidneys are not functioning properly. The blood creatinine level increases as the kidney disease progresses.

2. Blood urea nitrogen

Normal range: 7 to 20 mg/dL

Higher levels (greater than 20-40 mg/dL) may be suggestive of altered kidney function. Elevated BUN values may also be seen in dehydration, high-protein diet, severe burns, certain medications, etc.

3. Urinalysis

Typically, no or minor quantities of protein are present in the urine. A 24-hour urine collection contains less than 80 mg.

Normal value: 0 to 20 mg/dL

Persistent higher levels of protein and blood cells in the urine may indicate early signs of kidney diseases like chronic kidney disease, bladder infections, kidney stones, diabetic nephropathy, etc. A positive test for protein may also be seen after a heavy physical exercise, infection, etc.

4. Urea clearance

Normal range: 65 to 99 ml/min, i.e. your kidney removes all of the urea in 65-99ml of plasma in one minute.

A lower than normal urea clearance range may mean that your kidneys are not working properly. Higher levels may mean increased protein intake and breakdown.

5. Creatinine clearance

Normal values

Male: 85-125 ml/min

Female: 75-115 ml/min

Altered creatinine clearance range indicates altered kidney function. Low creatine clearance means that the ability of the kidneys to filter waste from the blood is reduced. Hence blood levels of creatinine and urea increase.

6. Glomerular filtration rate

Since blood creatinine alone is not a reliable measure of kidney function, eGFR is recommended as an index of its function1. GFR decreases with age even in the absence of kidney disease.

90-120 ml/min/1.73 m2: Normal range

60 and 89 mL/min/1.73m2: mild chronic kidney disease (CKD)

30 and 59 mL/min/1.73m2: moderate CKD

15-29 mL/min/1.73m2: Severe CKD

<15 mL/min/1.73m2: kidney failure (dialysis needed)

Reference

1. Lameire N, Adam A, Becker CR, Davidson C, McCullough PA, Stacul F, Tumlin J; CIN Consensus Working Panel. Baseline renal function screening. Am J Cardiol. 2006 Sep 18;98(6A):21K-26K. Epub 2006 Feb 20. Review. PubMed PMID: 16949377.

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