Stone Disease - Diagnosis

Kidney stones can take anywhere from weeks to years to develop. Furthermore, once formed, kidney stones can remain stable in size or continue to grow. Kidney stones that are tucked away in the kidney and not obstructing the flow of urine are usually not symptomatic. Blood in your urine may be the only sign.

If the stone causes an obstruction, though, it becomes symptomatic in a heart beat. A stone attack is heralded by an abrupt peak onset of pain called colic. Colic is characterized by crampy (intermittent) or constant back or abdominal pain. If the stone is in the kidney or upper ureter, the pain is usually centered in the flank (area below the rib cage on the affected side). If the stone is in the mid to lower ureter, the pain is usually located in the abdomen or ‘referred’ (radiated) to the groin. Finally, if a stone is lodged in the lower ureter, just outside the bladder, in addition to pain, the stone causes a constant urge to urinate because it irritates the bladder. Nausea and vomiting are two other common complaints that accompany stones regardless of their location.

X-ray studies are needed to verify the presence of a stone; determine its size, location; and ascertain the severity of obstruction. These studies may include one or more of the following:

IVP – Iodine dye is injected into an arm vein. The kidneys filter and excrete the dye. The dye is visible on x-ray films that outline the kidneys and ureters.
Helical (spiral) CT Scan – This x-ray study doesn’t require the use of dye. Instead, computer generated images demonstrate the kidneys, ureters, and surrounding structures.
Renal ultrasound – Using sound waves, a renal ultrasound outlines the kidney and surrounding structures. An ultrasound shows kidney stones bigger than 5 mm (size of a petite pea) and any urinary obstruction, but not necessarily the level of obstruction, especially if the obstruction is in the ureter.
KUB – Taken without dye, a KUB (also called a “flat plate”) consists of one or more x-ray films that show the kidney, ureter, and bladder - hence the name KUB. Although a KUB can detect calciumcontaining stones, it can’t visualize uric acid stones (discussed below) because they are radioluscent (invisible to x-ray).

Renal tomograms may also taken. A tomogram captures a particular part of the kidney in sharp relative to other parts of the kidney and surrounding tissue. Here’s how it works: The x-ray monitor is focused on a certain depth, then as the x-ray is being taken, the monitor moves to make the structures outside the focal area blurry relative to the area of interest.

Types of Stones

Although x-ray studies may suggest the stone composition, chemical analysis of the stone is the only way to accurately determine what kind of stone you have. Stones usually fall into one of the following categories:

Calcium-containing stone: About 80% of stones contain calcium combined with oxalate or phosphate
Uric acid stone: About 20% of stones are made of a breakdown product of purine metabolism called uric acid. Foods that are high in purine are listed in the stone prevention section.
Struvite: About 8% of stones are caused by urease-producing bacteria. However 60-90% of staghorn calculi - a special type of kidney stone with antler-like branches - are composed of struvite.
Cysteine: About 1% of stones are due to this inherited (autosomal recessive) disease.

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