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Membrane filtration in microscopical examination of urinary sediment
Abstract:
Microscopical examination of the urinary sediment has been performed after membrane filtration and after routine centrifugation, and the results were compared. Various quantities of urine were filtered through a membrane with pore size of 3 micrometer, stained with Shorr stain and made translucent with xylol. All granular and cellular casts were counted on a trimmed membrane, 15 X 20 mm. The routine centrifugation was carried out on 10 ml urine at 1500 rpm for 3 min. Among 11 patients with glomerulonephrits and recurrent hematuria, casts were found in 9 after filtration but in only 2 after routine centrifugation. Casts were detected by the filter method in the urine after angiography of the kidneys in 8 of 12 patients, after centrifugation in only one of them. No casts were found in 6 patients with hematuria due to urological disorders and in 21 healthy persons. The diagnostic sensitivity of microscopical examination of urine was greatly increased by the filter method. This may be due to larger amount of urine examined by the filter method, but an additional cause may be that routine centrifugation destroys red cell casts.
Insights
Membrane filtration significantly improves the detection of urinary casts compared to routine centrifugation. This enhanced diagnostic sensitivity is crucial for identifying kidney diseases like glomerulonephritis and hematuria.
Area of Science:
- Nephrology
- Urology
- Medical Diagnostics
Background:
- Microscopical examination of urinary sediment is vital for diagnosing kidney and urinary tract disorders.
- Current methods, such as routine urine centrifugation, may have limitations in detecting diagnostic elements like urinary casts.
- Urinary casts are critical indicators of various renal pathologies, including glomerulonephritis and hematuria.
Purpose of the Study:
- To compare the diagnostic efficacy of membrane filtration versus routine centrifugation for detecting urinary casts.
- To evaluate the impact of these methods on the diagnostic sensitivity for detecting casts in patients with hematuria and other renal conditions.
Main Methods:
- Urine samples were processed using both membrane filtration (3 micrometer pore size) and standard centrifugation (10 ml, 1500 rpm, 3 min).
- Urinary casts (granular and cellular) were counted after staining with Shorr stain and clearing with xylol for the filtration method.
- The presence of casts was compared between the two methods in patient cohorts with glomerulonephritis, recurrent hematuria, post-angiography, urological disorders, and healthy individuals.
Main Results:
- Membrane filtration detected casts in 9 out of 11 patients with glomerulonephritis and recurrent hematuria, compared to only 2 patients with routine centrifugation.
- In patients who underwent kidney angiography, casts were found in 8 out of 12 by filtration versus 1 by centrifugation.
- No casts were detected in patients with urological disorders or healthy controls by either method, confirming specificity.
Conclusions:
- Membrane filtration significantly enhances the diagnostic sensitivity for detecting urinary casts compared to routine centrifugation.
- The improved detection may be attributed to examining larger urine volumes and potentially preserving cast integrity, unlike centrifugation which might destroy red cell casts.