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Diagnosis of urolithiasis
Last reviewed: 04.07.2025
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Laboratory diagnostics of urolithiasis
The urinary sediment is examined, paying special attention to the salt crystals. Crystals of calcium oxalate monohydrate are oval in shape and resemble red blood cells. Crystals of calcium oxalate dihydrate are pyramidal in shape and resemble an envelope. Crystals of calcium phosphate are too small to be seen with a normal light microscope and resemble amorphous fragments. Uric acid crystals also usually resemble amorphous fragments, but they are typically yellow-brown in color. Less commonly, uric acid dihydrates may be rhomboidal or resemble hexagonal rhombuses on a deck of cards. Any of these crystals may be found in normal urine; their presence is not considered a diagnostic sign of the disease. However, cystine crystals always indicate cystinuria. Cystine crystals are flat hexagonal plates similar to benzene rings, but unlike them, the rings of cystine crystals may have equal or unequal edges. Crystals of ammonium phosphate with magnesium are shaped like rectangular prisms, similar to “coffin lids”.
If stones are present (either spontaneously or as a result of surgery), their chemical composition is determined. The stones are a mixture of minerals with organic substances, most often oxalates, phosphates, urates, carbonates are found in them. Less common are cystine, xanthine, protein, cholesterol stones. Stones are usually layered, the number of stone-forming minerals is no more than 3, the remaining minerals are found as impurities.
Oxalate stones
These stones are formed by calcium salts of oxalic acid, dense, black-gray, with a prickly surface. They easily injure the mucous membrane, as a result of which the blood pigment colors them dark brown or black.
Phosphate stones
Contain calcium salts of phosphoric acid. Their surface is smooth or slightly rough, their shape is varied, and their consistency is soft. They are white or light gray, formed in alkaline urine, grow quickly, and are easily crushed.
Urate stones
They consist of uric acid or its salts. The stones are yellow-brick-colored, of a hard consistency, with a smooth surface.
Carbonate stones
Formed by calcium salts of carbonic acid. They are white, with a smooth surface, soft, of various shapes.
Cystine stones
They consist of a sulfur compound of the amino acid cystine. They are yellowish-white, round, soft in consistency, with a smooth surface.
Protein stones
They are formed mainly from fibrin with an admixture of salts and bacteria. Small in size, flat, soft, white.
Cholesterol stones
They consist of cholesterol and are very rare in kidneys. They are black, soft, and crumble easily.
Instrumental methods for diagnosing urolithiasis
X-ray examination methods are widely used to diagnose urolithiasis. Calcium stones are detected on X-ray images of the kidneys, ureters, and bladder, but their types are not differentiated. Renal stones are easier to localize and identify on X-ray images of the kidneys, ureters, and bladder in combination with tomograms or using digital imaging methods of the kidneys, ureters, and bladder. Oxalate stones are usually small, dense, with clear boundaries. Cystine stones are poorly visible, soft, and waxy. Struvite stones (made of magnesium ammonium phosphate) are irregularly shaped and dense. Uric acid stones are transparent on X-rays and are not visible on X-ray images of the kidneys, ureters, and bladder.
Intravenous pyelography
It helps to clarify the location of urinary tract stones, the degree of obstruction and renal function. Radiolucent obstruction detected on a pyelogram suggests the presence of a uric acid stone. However, a non-contrast CT scan may be required to exclude a malignant tumor of the urinary tract epithelium. In the study of renal stones, the diagnostic value of ultrasound echography is less.
Ultrasound examination of the urinary system
Allows determination of obstruction as well as the size and location of larger stones.
Cystoscopy
It is indicated for the detection and extraction of stones from the urinary bladder, as well as the removal of stones from the ureters located near the ureterovesical junction.
Differential diagnosis of urolithiasis
If there are signs of renal colic, it is necessary to exclude diseases that occur with pain syndrome [cholelithiasis, acute appendicitis, myocardial infarction, duodenal and gastric ulcer, pancreatitis, psoas abscess, acute or exacerbation of chronic pyelonephritis, urotuberculosis, papillary necrosis, kidney tumors, renal infarction, thrombosis of the renal and hepatic veins, and in females (especially in adolescence) - gynecological diseases: acute adnexitis, ectopic pregnancy, ovarian cysts, endometriosis, etc.].
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