Manual of basic techniques for a health laboratory - libdoc.who.int

236 Manual of basic techniques for a health laboratorypH and crystalline depositsDetermination of the pH of urine is useful for the identification of crystallinedeposits (see section 7.2.7, pages 245–248).Some crystals are deposited only in acid urine, others only in alkaline urine.For example:— acid urine: oxalates, uric acid;— alkaline urine: phosphates, carbonates, urates.Except in very rare diseases, crystalline deposits in urine have no diagnosticsignificance.7.2.4 Detection of glucosePrincipleGlucose is the most commonly found sugar substance in urine, particularly in diabeticpatients and patients suffering from chronic renal failure. Glucose is a reducingsubstance. It reduces the blue copper sulfate in Benedict solution to red copperoxide, which is insoluble.Lactose is also a reducing sugar and is occasionally seen in the urine of pregnantwomen.Materials and reagents●●●●●●●Test-tubesWooden test-tube holderTest-tube rackBeaker or canBunsen burner or spirit lampDropper pipetteGraduated pipette, 5ml● Benedict solution (reagent no. 10).Fig. 7.5 Benedict method fordetection of reducingsubstances in urineMethod1. Pipette 5ml of Benedict solution into a test-tube.2. Add eight drops of urine and mix well.3. Boil over a Bunsen burner or spirit lamp for 2 minutes (Fig. 7.5), or placethe test-tube in a beaker or can of boiling water for 5 minutes.4. Place the test-tube in the test-tube rack and allow to cool to room temperature.Examine the colour change of the solution and any precipitate. Report theresult as shown in Table 7.1.Glucose in urine can also be detected using a urine dipstick (see section7.2.2).7.2.5 Detection and estimation of proteinElevated protein levels are observed in the urine of patients with:— urinary schistosomiasis— chronic renal disease