The kidneys' main function is to clear the blood of wastes and remove excess fluid. Some tests that measure abnormal kidney function include blood pressure, urine albumin, creatinine, glomerular filtration rate (GFR) and blood urea nitrogen (BUN). Abnormal values for any of these tests indicate different kinds of kidney diseases. Results not only help doctors diagnose different types of kidney diseases but also manage them as well.
Blood Pressure
High blood pressure is one of the main causes of kidney disease and, therefore, taking a patient's blood pressure is one of the main tests for kidney disease. Blood pressure is measured using a blood pressure cuff that is wrapped around the upper arm. Blood pressure is measured as two numbers. The top number, which is called the systolic blood pressure, is the pressure when your heart is beating. The bottom number called the diastolic blood pressure is the pressure when your heart is resting between beats. A single high reading may not mean you have high blood pressure. It should be confirmed by a doctor on another visit.
Urine Albumin
The urine albumin test examines urine for small quantities of a protein called albumin. Albumin in the urine indicates early kidney disease. A normal urine albumin level from a random urine sample is between 0 and 8 mg/dL. The urine albumin test involves normal urination into a cup. There is no discomfort and it can be done at home or in the doctor's office. If done at home, the sample must be taken to the doctor's office, where the doctor will insert a dipstick into the urine to test it for albumin.
If the level of albumin is abnormally high, some doctors may decide to repeat the test on a 24-hour urine sample. In this case, all urine output is collected during a 24-hour period and tested for albumin. Hospitalization is not a requirement for this test. A normal urine albumin level is less than 150 mg per 24 hours for a 24-hour urine collection. If necessary, the patient will be instructed to stop taking any medications that may interfere with the test results.
Creatinine
Normal muscle activity generates creatinine, a waste product found in the blood and eliminated by the kidneys in urine. If the kidneys do not function properly, creatinine builds up in the blood.
Measuring the amount of creatinine in the blood is done by taking a blood sample. A health care provider draws blood with a needle out of a vein from the inside of the elbow or the back of the hand. Once the blood is collected, the needle is removed and the site is covered with cotton wool to stop any bleeding. The blood sample is sent to the laboratory for testing. Normal blood tests for creatinine range from 0.6 to 1.2 mg/dL.
Measuring the amount of creatinine in your urine is done by taking a 24 hour urine sample. All the patient's urine is collected over a 24-hour period and tested for creatinine. The patient can collect their own urine at home and bring it to the doctors office. This requires normal urination. If necessary, the patient will be instructed to stop taking any medications that may interfere with the test results. Normal urine creatinine ranges from 500 to 2000 mg/day.
GFR
GFR is measured using a mathematical equation. The values for age, weight and gender along with a patient's blood creatinine can be plugged into a GFR calculator where the resulting value represents the patient's kidney function. The National Kidney Foundation considers GFR the best test to measure the level of kidney function. Normal GFR varies according to age, sex, and body size and ranges from 90 to 120 mL/min/1.73m2. Levels below 60 for three or more months are a sign of chronic kidney disease. Levels below 15 are a sign of kidney failure.
BUN
BUN measures the amount of urea in the blood. Protein intake causes a waste product in the body called urea. Under normal circumstances kidneys get rid of urea in the urine. If kidneys fail, urea builds up. Measuring the amount of urea in your blood is done by taking a blood sample from a vein from the inside of the elbow or the back of the hand. The blood sample is sent to the laboratory for testing. Generally, 7 to 20 mg/dL represents a normal range for BUN.
