Although kidney stones, or urinary calculi, usually do not cause any permanent damage, they can cause excruciating pain. Kidney stones form from minerals and acid salts present in urine. Common culprits include calcium oxalate, calcium phosphate, and uric acid. The stones form when levels of minerals and acid salts get too high, or when urine volume or anti-aggregation factors fall too low.
Purpose
Tests for kidney stones can prove the presence of a stone and allow differential diagnosis to rule out other conditions that cause some similar symptoms. The size of the stone determines if it can pass out of the body spontaneously, or if the patient will require interventional treatment. Further analysis allows the doctor to determine the exact chemical composition of the stone, which can guide recommendations such as diet changes to prevent more kidney stones from developing in the future.
Blood Tests
For patients with suspected kidney stones, the doctor will draw blood to test for the presence of high levels of calcium or uric acid, substances that commonly cause kidney stones. The blood test might also reveal underlying medical conditions that could predispose the patient to kidney stones. Measurement of kidney enzymes and metabolites in the blood provides insight into the overall health of the kidneys.
Urinalysis
People with kidney stones typically have pinkish colored urine because it is tinged with blood. Urinalysis can indicate the presence of urinary tract infections, a common cause or side effect of kidney stones. A doctor might suggest that a patient collect all of their urine for 24 hours. Analysis can determine if the patient has an excess of minerals or acid salts that cause stone formation, a lack of the normal components of urine that prevent aggregation of crystals.
Imaging
According to the Mayo Clinic, doctors might use an X-ray, or more commonly computerized tomography (CT) to see kidney stones. Visualizing the kidney stone pinpoints its location and allows an estimate of its size, both of which are variables that drive the treatment plan. Stones in the kidney are generally asymptomatic and require no treatment, according to the Merck Manual. Large stones lodged in the ureter might require surgery or procedures to break them into smaller pieces. Small stones in the ureter usually pass spontaneously and patients wait it out with help from pain medication.
Laboratory Analysis
Patients who know they have a kidney stone urinate through a special collecting sieve designed to catch the stone when it passes out of the body. Laboratory tests of the stone itself indicate its chemical composition. Calcium oxalate stones are the most common type, according to the Merck Manual.
