Kidney Stones - Risk Factors

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Urine Tests

Urine samples are needed to evaluate features of the urine, including its acidity and the presence of:

• Red or white blood cells
• Infection
• Crystals
• High or low levels of chemicals that inhibit or promote stone formation

Clean-Catch Urine Sample for Culturing. After determining that a kidney stone is present, the health care provider usually gives the patient a collection kit, including filters, to try to catch the stone or gravel as it passes out. The urine may also be tested (cultured) for the presence of infection-causing organisms. A clean-catch urine sample is almost always required for culturing. To provide a clean catch, do the following:

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• First, wash your hands thoroughly, and then wash the penis or vulva and surrounding area four times with downward strokes, using a new soapy sponge each time.
• Begin urinating into the toilet and stop after an ounce or two.
• Position the container to catch the middle portion of the urine stream.
• Urinate the remainder into the toilet.
• Tighten the cap on the container securely, being careful not to touch the inside of the rim.

Click the icon to see an image of a calcium urine test.

Twenty-Four Hour Urine Collection. A 24-hour urine collection may be needed to measure urine volume and levels of acidity, calcium, sodium, uric acid, oxalate, citrate, and creatinine.

• You should not change any of your usual eating or drinking patterns when performing this test.
• Discard the first urination on the day of the test.
• Afterward, collect all urine passed over the next 24 hours, including the first urination on the morning of the second day.
• A second 24-hour urine collection may be needed to determine whether treatment is working, or it may be done if the first analysis was not conclusive and the doctor suspects a less common stone, such as a cystine or xanthine stone.

Click the icon to see an image of a uric acid urine test.

Urine tests that are used to determine the specific chemical and biological factors causing the stone should be performed about 6 weeks after the attack, since the attack itself may change the levels of such substances, including calcium, phosphate, and citrate.