Stone Analysis Health Article

Definition

Kidney stones are solid accumulations of material that form through precipitation in the tubal system of the kidney. Kidney stones cause problems when they block the flow of urine through or out of the kidney. When the stones move along the ureter, they cause severe pain.

Gallbladder stones are also solid accumulations of material that form through precipitation in the liver and then move into the gall bladder. They cause problems when they block the flow of bile out of the liver or out of the gall bladder. They can cause attacks of gall bladder disease (cholecystitis), hepatitis or pancreatitis. They can also cause severe pain.

Purpose

The purpose of analyzing kidney and gallbladder stones is to determine the source of the stones. Different materials can form stones. Once the source of the stones is known, steps can be taken to prevent subsequent formation.

Precautions

An adequately stocked laboratory is needed for accurate analysis of stones. The most difficult aspect of stone analysis is obtaining the stones.

Passing a kidney stone is exquisitely painful. Once passed, persons with stones must strain their urine to recover any stones. Retrieving a kidney stone is painful for the person experiencing the stone. It also requires skill on the part of an operator to retrieve the stone.

A gallbladder stone must also be obtained before chemical analysis can be performed. Gallbladder stones can become lodges at several locations and cause considerable pain and discomfort. Retrieving a stone usually requires surgery. Commonly, the gallbladder is removed in the process of collecting a stone.

Kidney stones

Urine is formed by the kidneys. The kidney is made up of microscopic units called nephrons. Each nephron contains a capillary tuft (glomerulus) and a tubule. Blood flows into the kidneys, and engorges the capillary tufts. Water and small solutes pass through the vessel walls forming a filtrate of the plasma which enters the underlying space (Bowman's capsule). The walls of the capsule form a tubule that traverses the kidney. The cells of the tubule modify the filtrate along its length ultimately forming the urine which passes out of the body. Sometimes, a problem causes the dissolved solutes to become supersaturated resulting in the formation of crystals. When tiny crystals associate together they form a larger solid mass called a kidney stone or calculus. A kidney stone is also called a nephrolith or urolith (nephrorefers to the kidney, urorefers to urine, and -lith means stone). Kidney stones have multifactorial causes, but some predisposing conditions are:

• Diet: Excessive calcium in water and foods rich in oxalate or purines can lead to excessive excretion of calcium, oxalate and uric acid in urine.
• Dehydration: Water deprivation or loss from other sources causes stasis in the tubules and concentrates the solutes there.
• Deficiency of inhibitors: Some dietary substances such as ascorbic acid and citric acid promote loss of organic calcium salts that are soluble. Absence of these can lead to excessive amounts of oxalate and phosphate.
• Drugs: Some drugs such as tetracycline are poorly soluble and may precipitate forming stones or become part of the stone matrix.
• Metabolic disorders: Hyperparathyroidism causes excessive calcium excretion by the kidneys. Cystine stones form because of a defect in the renal tubular reabsorption of dibasic amino acids, a condition known as cystinuria.
• Genetics: Some people produce and excrete greater quantities of certain metabolites such as uric acid.
• pH: Most solutes are only soluble within a finite pH range. For example, phosphates and carbonates are insoluble at an alkaline pH. Uric acid and calcium oxalate are insoluble at an acidic pH. People who produce chronic acid urine are more prone to develop uric acid and calcium oxalate crystals.

Many people never find out that they have stones in their kidneys. These stones are small enough to allow the kidney to continue functioning normally, never causing any pain. These are called "silent stones." Kidney stones cause problems when they interfere with the normal flow of urine. They can block (obstruct) the flow down the tube (the ureter) that carries urine from the kidney to the bladder. The kidney does not normally experience any back pressure. When pressure builds from backed-up urine, the kidney may swell (hydronephrosis). If the kidney is subjected to this pressure for some time, it may cause damage to the delicate kidney structures. In the most severe case, this back pressure causes the pressure in Bowman's space to equal the blood pressure in the glomerular capillaries and filtration stops. The person stops producing urine, and waste products accumulate in the blood leading to renal failure. When the kidney stone is lodged further down the ureter, the backed-up urine may also cause the ureter to swell (hydroureter). Because the ureters are muscular tubes, the presence of a stone will make these muscular tubes spasm, causing severe pain.

About 10% of all people will have a kidney stone in their lifetimes. Kidney stones are most common among:

• Caucasians
• males
• people over the age of 30
• people who previously have had kidney stones
• relatives of persons with kidney stones