A kidney stone or renal calculus is a solid mass that consists of aggregates of crystals and small amounts of proteins and glycoproteins. The stones are solid concretions or calculi (crystal aggregations) formed in the kidneys from dissolved urinary minerals.

Kidneys filter waste products from the blood and add them to urine that the kidneys produce. When waste materials in urine do not dissolve completely, crystals and kidney stones may form. If stones grow to at least 2-3 millimeters they can cause obstruction. Pain due to kidney stones is most commonly felt in flanks, lower abdomen and groin.

What Causes Kidney Stones?

Kidney stones do not have single, well-defined cause, but are the result of a combination of factors. A stone is created when urine does not have the correct balance of fluid and a combination of minerals and acids, for e.g the pH level of urine. Alkaline urine tends to increase precipitation of calcium phosphate and may be responsible for calcium phosphate stones. Kidney stones are formed when there is an alteration in the relative proportions of crystalloids and glycoaminoglycans in the urine.

Conditions associated with the formation kidney stones are:

• Obstruction of the urinary tract
• Infection of the urinary tract
• Climate or occupation giving rise to excessive sweating
• Inherited disorders like cystinuria and xanthinuria
• Hyperparathyroidism, medullary sponge kidney, renal tubular acidosis, Dent’s disease.

Types of Kidney Stones:

• Calcium Stones: Approximately 85% of stones are composed predominantly of calcium compounds.

The most common cause of calcium stone production is excess calcium in the urine (hypercalciuria).

o Calcium phosphate stones are very common and easily dissolve in Vitamin C acidified urine.
o Calcium oxalate stones are common. Oxalate is present in certain foods. Diseases of the small intestine increase the tendency to form calcium oxalate stones. These stones do not dissolve in acidified urine.
• Struvite stones (Magnesium ammonium phosphate) are not very common. Struvite stones are mainly found in women after a urinary tract infection. They can grow very large and may obstruct the kidney, ureter or bladder. They dissolve in vitamin C acidified urine.

• Uric acid stones result from difficulty in metabolizing purine (the chemical base of adenine, xanthine, theobromine [in chocolate] and uric acid). They may form in a condition such as gout.

• Cystine stones are rare and may form in persons with cystinuria. It is a hereditary disorder affecting both men and women due to an inability to reabsorb cystine. Children usually suffer from these types of stones.

Signs and Symptoms of Kidney Stones:
There may be severe tenderness of the abdomen or back. If the stones are big, persistent, or recurring, there may be signs of kidney failure or other kidney diseases.
In most cases, the first symptom of kidney stones that people experience is extreme pain, which occurs when a stone acutely blocks the flow of urine. However, they may not produce any pain until they begin to move down the ureter.
Following are the most common symptoms of Kidney Stones:

• Pain, usually severe and often starts in the flank region, and moves down to the groin. Pain in the back and flank may be bilateral or unilateral.

• Pain may be progressive, severe, colicky (spasmodic) or pricking.

• Vomiting and nausea may be present.

• Excessive and painful urination.

• Increased frequency or urgency of urination.

• Pain in the abdomen.

• Blood or abnormal color of urine.

• Fever with chills may be present. In this case, an infection may be present.

Diagnosis of Kidney Stones:

Diagnosis of renal stone disease involves a medical history, physical examination, laboratory evaluation, and imaging tests.
Following tests help in diagnosing kidney stones:

--Routine analysis of the urine may reveal the type of stone, levels of calcium, phosphate and oxalate, and protein loss if any.

--Ultrasound scan

--Intravenous pyelography

--X-ray of the abdomen

--C T Scan of the abdomen

--MRI of the abdomen

--Retrograde pyelogram
Laboratory tests include a urinalysis to detect the presence of blood (hematuria) and bacteria (bacteriuria) in the urine. Other tests include blood tests for creatinine (to evaluate kidney function), BUN and electrolytes (to detect dehydration), calcium (to detect hyperparathyroidism), and a complete blood count (CBC; to detect infection).

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