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

7. Examination of urine 2357.2.3 Measuring the pHNormal freshly passed urine is slightly acid, with a pH ofaround 6.0.In certain diseases the pH of the urine may increase ordecrease.Principle● Coloured indicator paper is dipped in the urine (or placedin a watch glass and a few drops of urine are added to it).● The colour changes according to the pH.● The paper is then compared with a standard control chartgiving the corresponding pH value.Fig. 7.1 Materials for measuring the pH of urineMaterials (Fig. 7.1)●●●Watch glassesDropperForceps● Universal indicator paper (for measuring pH from 1 to10)● Indicator paper of limited pH range: for the 5.0–7.0 rangeand for the 6.0–8.0 range.The urine specimen must be tested within 1 hour ofcollection.Fig. 7.2 Applying the urine specimen to universalindicator paperMethod1. Place a strip of universal indicator paper in a watch glass.Let a few drops of fresh urine fall from the dropper on tothe paper (Fig. 7.2).Alternatively, dip the test paper directly into the urine inthe receptacle.2. Pick the strip of paper up with forceps.Compare the colour obtained with those shown on thestandard chart (Fig. 7.3). Read off the pH unit given forthe colour that matches the test paper most closely.3. According to the result obtained, select a strip of indicatorpaper for the corresponding limited range. For example,if the pH is 6, use indicator paper for the range 5.0–7.0.If the pH is 7 or more, use indicator paper for the range6.0–8.0.4. Repeat the test in another watch glass, using the paperfor the corresponding limited range. Read off the pH ofthe urine on the standard chart (Fig. 7.4), e.g. pH = 6.2or pH = 7.5.The pH of urine is normally about 6.0 (range 5.0–7.0). AcidpH values (4.5–5.5) are observed in some forms of diabetes,muscular fatigue and acidosis. Alkaline pH values (7.8–8.0) are common in patients with infections of the urinarytract and in people on a vegetarian diet.Fig. 7.3 Checking the pH using universal indicatorpaperFig. 7.4 Checking the pH using indicator paper oflimited pH range