Urine 24-hour Collection, and Preservatives
- Please provide the following written instructions to the patient for the collection of 24 hours of urine collection.
Purpose of 24-hour urine collection
- 24-hour urine collection’s main purpose is quantitating certain substances excreted in the urine.
- Urine samples may also be collected for 1 and 4 hours.
- It helps in assessing kidney function.
Precautions for Urine 24 hours
- A complete and accurate collection must be made to evaluate the required test on 24-hour urine samples properly.
- Drink fewer fluids during the collection time unless advised by the doctor.
- Avoid alcoholic drinks.
- Avoid certain foods, beverages, and medication that may affect the result.
- Do not test the chemicals needed before the required time of collection because the excretion of the substance in the urine varies.
Container for urine collection
- Urine containers should be clean and sterile. It should have a tightly fitting lid to avoid evaporation, contamination, and spillage of urine.
- Label the urine bottle with name, age, sex, and date of collection.
- For a 2-hour urine collection, the one-liter container is sufficient.
- For 12-hour collection, the 2-liter container is sufficient.
- For 24-hour collection, you may need a 3 to the 4-liter container.
- A single container is preferred because of the mixing of the analytes needed for estimation.
- The single container also avoids the loss of urine.
Procedure for 24-hour urine collection
- Empty the urinary bladder when you get up in the morning.
- Note the time …………… and date ………..
- Discard the first urine in the urinary bladder (empty bladder), and start the clock.
- Thereafter, collect all the urine samples in the container.
- Now onward, collect the urine in a clean bottle or container.
- Collect all the urine passed during the day and night.
- Note the time, which will be the same………….. and date (after 24 hours) …………..
- Empty your bladder in the container (last-moment urine sample). Make the final collection of urine at the same time.
- Keep the urine in the refrigerator and, if possible, bring it to the laboratory as soon as possible after the collection.
- There may need to add chemicals like hydrochloric acid or boric acid in some of the tests as preservatives.
Purpose of urine preservative:
- Preservatives prevent bacteria growth.
- Preservatives prevent the decomposition of the substance to be tested.
- Preservative prevents from precipitation of the substance to be tested.
- Refrigeration during and after urine collection is the best preservative.
- Acidification of the urine (pH below 3) is used for calcium, steroids, and VMA.
- Sodium hydroxide (NaOH) is used for porphyrins, urobilinogen, and uric acid testing.
Mechanism of urine preservatives:
- Urine preservatives work:
- Prevents decomposition of the urine.
- Prevents the growth of bacteria.
- Prevents the metabolism of the microorganism.
- Hydrochloric acid (HCL) 6 mol/L, needed 30 mL for 24- hours urine sample.
- Boric acid 10 grams per 24-hour needed.
- Nitric acid (HNO3) 6 mol/L, 15 mL needed for 24-hour urine.
- Sodium carbonate (Na2CO3) 5 grams needed for 24-hour urine.
- Acetic acid 50%, 25 mL needed for 24-hour urine.
Urine preservative for various chemicals:
|Chemical to be tested||Preservative||Instructions|
|Calcium||25 mL of 6 M HCL||
|Magnesium||25 mL of 6 M HCL||
|Phosphorus||25 mL of 6 M HCL||
|Glucose||No need; keep it in the fridge|
|Amylase||No need; Keep it in the fridge|
|Protein and albumin||No need; Kepp it in the fridge|
|Sodium, Potassium, Chloride||No need|
Normal urine picture:
|Physical features||Chemical features||Microscopic findings|