Kidney stones (Diagnosis)

What tests are done to diagnose kidney stones?

Health care professionals may use lab or imaging tests to diagnose kidney stones.

1. Urine tests:

These tests check for abnormality in urine which may indicate presence of blood, infection or stone forming minerals.

• Urine routine:

– Blood cells (RBCs) which indicate blood in urine

– Increased pus cells (WBCs) which suggests infection

– pH of urine which suggests if the urine is acidic or alkaline

– Color, which can be cloudy in case of infection or red/brown for blood

• Urine culture: may establish presence of infection.

• 24 hour urine test: may show presence of excessive stone forming minerals in urine or lack of stone preventing substances. The doctor may ask ask to collect the sample on two consecutive days.

2. Blood tests:

It can show high levels of stone forming minerals in blood such as calcium, phosphorus or uric acid. If serum calcium levels are found high then blood test for parathyroid hormone is done. Blood test measuring serum creatinine and blood urea (renal function test ) can indicate the health of the kidney.

3. Stone analysis:

This test analysis the constituents of the stone which helps to determine the cause of stone formation. This further helps to guide treatment and prevent formation of stone. It is done after the stone is passed out through urine or is taken out of the body by surgery.

Know more about stone analysis

4. Imaging tests:

• X-ray KUB: is the basic test often done to check for presence of any obvious stone in the region of kidney, ureter or urinary bladder. It can’t detect small stones or stone obscured by overlying gas in the intestines.

• Ultrasound abdomen/KUB: often the first test to be done to detect stone or to rule out obstruction by stone. It can detect stone in the urinary bladder and usually stones of size 5mm or more in the kidneys. A significant sized stone in the ureter can also be picked by the USG unless it becomes difficult due to overlying gases in the intestines and abdominal fat. In such cases CT scan is done to confirm the presence of stone. However, in children and pregnant women it is the preferred test.

• CT scan: this is most accurate test done to detect or rule out a stone. If a stone is present CT can accurately determine the size, location, density and obstruction caused by the stone. The only downside is the high amount of X-rays used to perform the test. Sometimes a dye is also injected into the blood of the person to check for the functioning of the kidney. This test is called as CT urography test.

• Others: less often IVP (intravenous pyelonephrography) is done now a days or in special cases MRI abdomen.