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Calcium oxalate crystallization in untreated urine, centrifuged and filtered urine and ultrafiltered urine.

Author(s): Guerra A, Meschi T, Allegri F, Schianchi T, Adorni G, Novarini A, Borghi L

Publication: Clin Chem Lab Med, 2004, Vol. 42, Page 45-50

PubMed ID: 15061379 PubMed Review Paper? No

Purpose of Paper

Conclusion of Paper

Studies

1. Study Purpose

   This study compared calcium oxalate crystal formation in untreated; centrifuged and filtered; and centrifuged, filtered, and untrafiltered urine from healthy patients spiked with sodium oxalate. The pH of first-morning urine from 17 healthy men was adjusted to 5.7 and aliquoted. Aliquots were left untreated or centrifuged at 2000 rpm and filtered through a 0.22µm filter only or followed by ultrafiltration using a Centricon -10 filter (10,000 kDa). Sodium oxalate was added to aliquots of specimens to achieve 0.3-1.5 mmol/L oxalate and placed in a shaking water bath at 37˚C for 3 h before microscopy.

   Summary of Findings:

   Centrifuged and filtered urine that was not ultracentrifuged had significant amounts of precipitate attached to the tube and the authors report that in cases with high CaOx relative supersaturation, the precipitate covered the bottom of the tube. In contrast, untreated urine had a smaller number of crystals which were larger and did not adhere as strongly to the tube and ultrafiltered urine had fewer crystals and aggregates which did not adhere to the tube.  The percentage of the microscopic field occupied by calcium oxalate dihydrate crystals (COD) and calcium oxalate monohydrate crystals (COM) was significantly higher in urine centrifuged and filtered but not subjected to ultrafiltration than in urine that was untreated or urine that was centrifuged, filtered, and then ultrafiltered (70.7% versus 13.2% and 11.1%, respectively, P<0.0001), but the difference between untreated urine and urine that was ultrafiltered was not significant. The ratio of the area occupied by COD crystals to the area occupied by COM crystals was significantly higher in untreated urine than centrifuged urine that was filtered through a 0.22 µm filter only (71.4% versus 0.0026%, P=0.029) or filtered and then ultrafiltered (71.4% versus 5.5%, P=0.034) and also urine that was ultrafiltered compared to urine not ultrafiltered (5.5% versus 0.0026, P=0.019). The diameter of COD and COM crystals was higher in ultrafiltered urine than untreated urine (24.3% versus 15.2%, P=0.005 and 8.9% versus 5.2%, P=0.0001, respectively) or urine that was centrifuged and filtered but not ultrafiltered (24.3% versus 3.7%, P<0.05 and 8.9% versus 2.6%, P<0.0001, respectively) and higher in untreated urine than urine that was centrifuged and filtered but not ultrafiltered (15.2% versus 3.7%, P=0.005 and 5.2% versus 2.6%, P=0.015, respectively). The percentage of the microscopic field occupied by COD and COM aggregates was higher in urine centrifuged and filtered but not subjected to ultrafiltration than in untreated urine (22.1% versus 8.5, P=0.020) or urine subsequently ultracentrifuged (22.1% versus 2.9%, P=0.001) and higher in untreated urine than ultrafiltered urine (8.5% versus 2.9%, P=0.0001). In ultracentrifuged urine, CaOx relative supersaturation was correlated with the percentage of the field occupied by CaOx crystals (r=0.59, P<0.05), the ratio of the COD area to the COM area (r=0.54, P<0.05), and the COD diameter (r=0.71, P<0.01), but urine CaOx relative supersaturation was only correlated with the ratio of the COD area to the COM area (r=0.70, P<0.05) and the percentage of the field occupied by CaOx crystals (r=0.55, P<0.05) in untreated urine and urine that was only centrifuged and filtered, respectively.

   Biospecimens

   • Bodily Fluid - Urine

   Preservative Types

   • None (Fresh)

   Diagnoses:

   • Normal

   Platform:

   Analyte	Technology Platform
   Morphology	Macroscopic observation
   Morphology	Light microscopy

   Pre-analytical Factors:

   Classification	Pre-analytical Factor	Value(s)
   Biospecimen Aliquots and Components	Filtration	Unfitered 0.22µM filtered 0.22µM filtered and ultrafiltered at 10,000 Da
   Biospecimen Aliquots and Components	Centrifugation	Centrifuged Not centrifuged

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