Sediment Information and Courses from MediaLab, Inc.

If leukocyte esterase is detected, a color change occurs on the reagent pad after the strip is dipped in the urine sample. Be sure to follow the manufacturer's directions for read-time and test interpretation. A positive leukocyte esterase test indicates the presence of granulocytic white blood cells. Lymphocytes do not contain granules, and would not produce a positive leukocyte esterase test. Positive results should be confirmed by performing a microscopic examination on the sediment; being aware that white blood cells may be absent if they are lysed, yet releasing their esterases into the specimen. Positive results may occasionally be found in random specimens from females due to contamination of the specimen by vaginal discharge.

The following factors promote the formation of casts in the kidney:Larger than normal amounts of plasma proteins entering the tubules,Decreased pH.Decreased urinary flow rate.Increased urine concentrationAfter formation, casts are washed loose from the tubules and discharged into the urine, where they can be found its sediment.

The urine microscopic exam is performed on a centrifuged urine sediment. The sediment contains all the formed elements or insoluble materials that have accumulated in the urine through its passage from the kidney to the lower urinary tract. These formed elements include cells, casts, crystals and miscellaneous structures.

Examination of a fresh urine specimen provides the best results. If a specimen cannot be examined immediately, it may be refrigerated for up to 12 hours. Refrigeration prevents decomposition of casts, cells and the overgrowth of bacteria. The urine sediment elements begin to lyse after 1-3 hours at room temperature. Although the most commonly received urine specimen is the random urine collection, the specimen of choice for urinalysis is the first morning urine. The first morning urine is more concentrated and allows for the detection of substances which may not be present in a more dilute random sample. Once the physical and chemical characteristics of the urine have been determined, the microscopic exam is performed on the sediment.

Urine sediment may also contain white blood cells (WBCs). Most of the WBCs in urine are segmented neutrophils. Since it is possible that lymphocytes, monocytes, and/or eosinophils may be present, the cells in urine can be stained if it is necessary to differentiate them. The segmented neutrophil just above center of the image to the right shows a distinct nucleus. When viewing urinary sediment under the microscope, the fine focus adjustment must be used to identify white blood cells. White blood cells swell in dilute alkaline urine and the cytoplasmic granules exhibit brownian movement resulting in “glitter cells.” These cells lyse rapidly. “Glitter cells” are most easily seen when viewed under phase-contrast microscopy.

Cells which may be present in the urine include epithelial cells, white blood cells (WBC) and red blood cells (RBC). The epithelial cells in the urine may originate from any site in the genitourinary tract. It is normal to find a few epithelial cells in the sediment. White blood cells may enter the urinary tract anywhere from the glomerulus to the urethra. The WBCs are mostly neutrophils. Red blood cells may originate in any part of the urinary tract. Normally, RBCs do not appear in the urine, although the presence of a few RBCs is not considered abnormal.

The following table lists common crystals found in the urine sediment. Crystals that have no clinical significance must be identified and differentiated from those that can be an indication of a metabolic disorder or other clinically significant conditions. Crystal pH Color Uric Acid Acidic Yellow - Brown Calcium Oxalate Acidic/Neutral Colorless Amorphous Urates Acidic Yellow - Brown Triple Phosphate Alkaline Colorless Ammonium Biruate Alkaline Yellow - Brown Amorphous Phosphate Alkaline/Neutral White - Colorless Calcium Carbonate Alkaline Colorless

In order for a urinalysis to be useful a physician must know not only what elements are present but the quantity of each. This section will deal with counting and estimating the microscopic elements found in the urine sediment. The quantifications may vary slightly between laboratories, but each lab should have its own criteria. Quantitation may be divided into three steps: Looking for casts Counting elements Estimating elements

Supravital stains are available for examining wet preparations or staining preserved slides. They increase the overall visibility of the elements by increasing the refractive index. Permanent slides can be made by using the cytocentrifugation technique and staining with Papanicolaou's stain to provide even more standardized sediment and uniform stain.

Parasites which may be found in urinary sediments include Trichomonas vaginalis, Enterobius vermicularis and Schistosoma haematobium. It is also important to note that parasites and parasitic ova may be seen in urine sediments as a result of fecal or vaginal contamination. This slide shows examples of Trichomonas vaginalis. In the female, Trichomonas is usually found as a contaminant from vaginal infection and is often accompanied by an increase in the number of white cells. Trichomonas is highly motile, measuring 5 - 15 microns with a characteristic pear shape. It has multiple anterior flagella and the nucleus is often apparent.