Kidney stones (nephrolithiasis): causes, examination, prognosis
Kidney stones are crystallized components of urine that can form in the kidneys, renal pelvis and the urinary tract. Only when they migrate into the ureter do kidney stones cause pain – severe cramps in the flanks, accompanied by nausea and vomiting (renal colic). About twice as many men as women develop kidney stones. The cause is a supersaturation of the urine with stone-forming substances. Read more about kidney stones.
Kidney stones: Description
Kidney stones (renal gravel) are deposits that are formed from components of the urine. They can occur in the channels of the kidney, in the renal pelvis and in the urinary tract. Some are only as small as grains of rice, others can fill the entire renal pelvis (sink stones).
Kidney stones are considered a disease of affluence: protein-rich nutrition, over-nutrition, obesity (adiposity) and lack of exercise promote the formation of kidney stones.
Kidney stone composition
Depending on the composition, physicians distinguish different types of kidney stones:
- Calcium-containing stones: They make up 70 to 80 percent of all kidney stones. By far the most common are calcium oxalate stones, followed by calcium phosphate stones.
- Uric acid stones: represent about 15 percent of all kidney stones, they are also called urate stones.
- Magnesium ammonium phosphate stones: Their share is about 10 percent. Other names are struvite or infection stones.
- Cystine and xanthine stones: They account for only about two percent of all kidney stones.
Kidney stones: Frequency
Kidney stones are by far the most common kidney disease: about five percent of adults in Germany are affected. Kidney stones usually occur between the ages of 30 and 60, about twice as frequently in men as in women.
Kidney stones: symptoms
You can read all the important information about possible symptoms of kidney stones in the article Kidney stones – symptoms.
Kidney stones: causes and risk factors
Kidney stones develop when certain substances are present in urine in too high concentrations. They precipitate in initially small crystals, which grow and merge over time – first kidney gravel is formed, then finally kidney stones are formed.
The causes of the supersaturation of the urine with stone-forming substances are
- Increased excretion of stone-forming substances (such as calcium, phosphate, oxalate, uric acid) and reduced excretion of non-stone forming substances (magnesium, citrate)
- Increased urine concentration due to dehydration (heavy sweating), tropical climate or chronic intestinal diseases
- Disorders of calcium metabolism, for example due to hyperthyroidism with increased calcium excretion
- Disturbances of the uric acid metabolism with increased uric acid excretion, which are either based on enzyme defects or are favoured by a purine-containing diet (meat!), alcohol abuse or the decay of tumour tissue
- Urine with a pH of less than 5,5 (for uric acid stones) or more than 7,0 (for phosphate stones)
Risk factors of kidney stone formation
Various factors favour the formation of kidney stones, including:
- Foods that dehydrate the body and saturate the urine with salts (e.g. asparagus, rhubarb)
- Urinary retention due to scars, constrictions or malformations in the kidneys or urinary tract
- Food supplements containing calcium and vitamin D
- Certain drugs such as acetalzolamide, sulfonamides, triamterene, indinavir and extremely high doses (over 4 grams per day) of acetylsalicylic acid (ASA)
- Occurrence of kidney stones in family members
- Repeated urinary tract infections
- Too little liquid absorption
Kidney stones: examinations and diagnosis
In many cases, the patient’s medical history already provides evidence of kidney stones. The actual diagnosis is made by the doctor using imaging techniques.
A common method of diagnosing kidney stones is ultrasound examination of the urogenital tract, which is often combined with X-ray examination of the kidneys, ureters and bladder.
Another diagnostic procedure is the excretory urography of the kidney and the urinary tract with X-ray contrast medium. The administration of contrast medium is not possible for people with contrast medium allergy or pre-existing kidney function impairment without extensive protective measures. For this reason, spiral CT, a modern form of computed tomography (CT), is increasingly recommended. This technique does not require a contrast medium and can be used as an alternative to urography.
Depending on the individual case, further examinations are necessary to diagnose kidney stones, for example a cystoscopy with X-ray imaging of the urinary tract from the bladder (retrograde ureteropyelography) or a scintigraphy (a nuclear medical examination procedure).
If kidney disease is suspected, the urine is examined for blood, infections and chemical changes. Urine is also collected at least once over 24 hours in order to calculate the daily excretion of certain substances. Blood tests help to assess kidney function and to identify concomitant inflammation and possible metabolic diseases as the cause of kidney stones.
People with kidney stones should use a sieve when urinating to catch stones or parts of them when urinating. An examination of the deposits in the laboratory can provide information about the exact cause of stone formation. Then the kidney stones can be treated specifically, or the development of further stones can be prevented.
Kidney stones: Treatment
You can read everything important about the therapy of kidney stones in the article Kidney stones – treatment.
Kidney stones: course of disease and prognosis
Kidney stones can occur again and again. After successful treatment, 50 percent of patients experience stone formation again within ten years. However, this high relapse rate can be significantly reduced by good stone prophylaxis.
Kidney stones can, for example, lead to inflammation of the renal pelvis (pyelonephritis), to blood poisoning due to inflammation of the urinary tract (urosepsis) and to constrictions in the urinary tract. In very serious cases, kidney stones can cause acute kidney failure.