Biochemistry – Urine Analysis


General urine examination includes macroscopic, chemical and microscopic urinalysis. The macroscopic analysis includes examination of urine appearance and colour. The chemical examination includes specific gravity, qualitative presence of proteins, blood, nitrites, glucose, ketones, bilirubin, urobilinogens, etc. The microscopic examination refers to the presence of erythrocytes, leukocytes, epithelial cells, cylinders, bacteria, crystals, etc.


Urine sediment is obtained from urine centrifugation, and it represents organized or biological and unorganized or chemical sediment. Organized urine sediment is the number of leukocytes, erythrocytes, epithelial cells, cylinders, bacteria, fungi, parasites and sperm. Unorganized urine sediment contains crystals of various salts (oxalate, phosphate, urate, and other salts.) Clinical importance of the organized sediment is more important than the unorganized one.


The differentiation of cells present in urine may be performed in a native preparation or in a stained preparation (staining of the nuclei is particularly important, as it is well noticeable when the sediment is held in a toluidine blue solution). Urine cytology is extremely important for the differential diagnosis of the disorders of the urogenital tract. For example, in acute pyelonephritis, in addition to neutrophilic leukocytes in urine also appear leukocyte or bacterial cylinders, bacteria and proteins, while lower urinary tract infections contain no proteins.


Urine sediment normally contains less than 5 leukocytes per field of view. A larger number of leukocytes is abnormal. Leukocytes may originate from anywhere along the urinary tract or may be a product of the genital tract secretion. The sediment most often contains neutrophilic leukocytes. An increased number of leukocytes in the sediment is the result of an infection of any part of the urogenital tract, when except leukocytes bacteria may also be found.


If there are more than 3 erythrocytes per field of view, this is treated as a form of hematuria. Hematuria is a sensitive early indicator of kidney diseases caused by an infection, tumor, stones or generalized bleeding disorders or overdosed anticoagulant therapy. Hematuria can be also detected in acute glomerulonephritis, pyelonephritis, urolithiasis, renal tuberculosis and other kidney diseases.


In case of nephron damage, kidney filtration becomes less selective which gives those blood parameters in urine which normally should not appear in urine such as e.g. proteins. At the beginning of a kidney disease, urine first contains proteins of the low molecular weight such as microalbuminuria and albumin, whereas a considerable renal failure results in non-selective proteinuria, and urine also contains proteins of the higher molecular weight such as immunoglobulins.

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