Analysis of 24-hour urine composition is widely used in diagnosis of acute and chronic kidney diseases. In Sri Lanka, no guidelines are available on preservation of urine. This study aimed to identify an effective preservation technique/s among currently practiced techniques in laboratories to maintain chemical stability of high demand bio chemical analytes in a 24-hour urine collection. An experimental study was undertaken using urine samples from volunteers (n=42, National Hospital of Sri Lanka and University of Sri Jayawardenepura, Nugegoda, Sri Lanka). Each sample was divided in to 10 ml aliquots; Out of the lot, one was preserved without any preservative and another refrigerated at 4ºC for 24 hours. Other aliquots were preserved for 24-hours by addition of following preservatives in a 24-hour collection: boric acid g/ urine (5, 7.5, 10), sodium azide g/ urine (0.3, 0.6, 0.9), HCl ml/ urine (1N;10ml, 6N;10ml, 25ml and 30ml). The aliquots with preservatives were kept at room temperature for 24 hours. Protein, Creatinine, Ca2+, Mg2+ and PO4 3- concentrations were measured in each aliquot. Least mean squared error for each analyte in different preservatives was calculated. For protein and creatinine, least mean squared error was given by, 10g/L boric acid. That of Ca2+, Mg2+ and PO4 3 were observed when the sample was refrigerated or after addition of 10g/L boric acid as the preservative. Conclusions Sodium azide and HCl that are utilized in current practice as preservatives for 24-hour urine collections do not show better performance in selected analytes. Boric acid (10g/L) is more effective in persevering protein and creatinine. Due to practical issues in acquiring refrigeration facilities, Ca²⁺ , Mg²⁺ and PO₄^3- also can be preserved effectively by using the same preservative. Consequently, Boric acid (10g/L) could be recommended as an effective preservative to preserve selected analytes in 24-hour urine collection.

Keywords
Urine preservatives , 24-hour urine collection , Boric acid , Creatinine