Sample collection: A 24 hour urine sample is collected on ice to prevent bacterial growth.
Method:
(1) An aliquot of the 24 hour urine is taken, typically 25 mL.
(2) 10 grams of potassium oxalate powder is added and mixed to precipitate calcium.
(3) The pH of the urine sample is taken using a pH meter with a glass electrode.
(4) If acidic, then the pH is titrated to 7.4 using 0.1 N NaOH. If the pH is > 7.4, then the test is not applicable.
(5) The volume in mL of the NaOH needed to neutralize the specimen is recorded.
titratable acidity in mL 0.1 N NaOH =
= (mL of NaOH used to titrate sample to pH 7.4) * (24 hour urine volume in mL) / (volume of urine sample in mL)
titratable acidity in mL 0.1 N NaOH per kilogram body weight =
= (titratable acidity in mL 0.1 N NaOH) / (body weight in kilograms)
titratable acidity in mEq per 24 hours =
= (titratable acidity in mL 0.1 N NaOH) * 0.1
Reference range for titratable acidity:
• 200 – 400 mL 0.1 N NaOH per 24 hours
• 20 - 40 mEq per 24 hours
• approximately 6 mL 0.1 N NaOH per kilogram body weight per 24 hours
