Urine changes When Urine Left at Room Temperature, and Preservatives
Urine changes When Urine Left at Room Temperature and Without Preservatives
Definition of the urine analysis
- Urine analysis is one of the most important tests without any injury to the patient.
- This simple test will discover any disease in the entire urinary tract.
Precautions in the collection of urine:
- Proper collection and the handling of the urine are important to get accurate results. It depends upon:
- The containers used should be clean, dry, and proper for the sample.
- Should follow proper collection procedure.
- Storage conditions are also important.
- A suitable preservative is also important to get accurate results.
- Disposable inert plastic containers with a secure cap are the best for urine collection.
- Biochemical and microbiological changes occur when urine is left in the lab at room temperature for a longer period (maybe over 24 hours).
- For routine urine analysis, freshly voided urine is better than the catheterized sample.
- Avoid urine contamination from the vaginal secretion (discharge) or hemorrhage.
- Get the clean voided midstream urine, particularly for the bacteriological examination.
- It may be needed to pack the vagina or use the tampoon to avoid vaginal contamination.
- The best sample to check urine glucose is one voided 2 to 3 hours after the last meal.
- This is the exception of the early first-morning sample.
The key importance is to check the fresh or suitably preserved urine, usually refrigerated.
- Examine urine within 30 minutes of the collection, as the changes (decomposition) start during this time.
- Try to examine the urine in the first 1 to 2 hours of collection.
- Urine is the best culture media for the growth of bacteria.
- If it is delayed, then refrigerate the urine at 4 °C.
- Urine left at room temperature >2 hours is not acceptable.
- Urine preservatives are only accepted for 24 hours of urine collection, not for routine examination.
Urine sample to be rejected:
- When urine has incorrect preservatives.
- When the urine quantity is insufficient.
- When urine is not collected with all needed precautions.
- When there is a missing or incomplete request form.
- When urine has no proper identification.
- When urine shows contamination like stool, etc.
Some articles favor that urine should be examined within two hours of collection.
Urine changes when collected and left in the lab (at room temperature):
- Appearance: Urine normally becomes hazy or cloudy when left at room temperature. This can be reversed by adding a few drops of acid.
- Vaginal contamination is quite a common cause of cloudy urine in female patients.
- After the food (vegetable/meat), urates or phosphate may produce cloudiness in the urine.
- Color: The normal color of the urine darkens on standing for longer than 30 minutes due to oxidation of urobilinogen to urobilin.
- Some foods like beets can cause red-colored urine.
- Odor: If urine is kept for a long time at room temperature, it will give an ammonia smell produced by the bacteria, which will decompose the urea in the urine.
- pH: Growth of the proteus will change the pH into alkaline.
- If urine is left at room temperature after sometimes it will become slowly alkaline due to bacterial growth.
- After keeping the urine on the table at room temperature become alkaline due to urea-splitting enzyme by the bacteria.
- Specific gravity: When urine is kept in the fridge, it will increase the specific gravity (false value).
- Red blood cells: These are distorted because of the lack of isotonic solution.
- RBCs become crenated or swell, which makes them difficult to recognize.
- Finally, RBCs disintegrate.
- White blood cells: When is kept at room temperature >2 hours will disintegrate the WBCs.
- WBCs will also disintegrate in a hypotonic solution.
- Cast: These will disintegrate, especially as the urine becomes alkaline, but these casts need acidic urine and solute for their existence in the urine.
- The alkalinity of urine: Other substance which appears in the acidic urine will disappear in the alkaline urine.
- Alkalinity develops because of the growth of the bacteria and the production of ammonia.
- Bacteria: These will multiply and obscure the various components.
- Glucose: After some time, urine glucose decreases due to glycolysis and utilization by the bacteria.
Changes when urine is left for a longer period at room temperature:
|Urine Substance||Changes taking place||How change takes place (a mechanism)|
|pH||It will increase and is alkaline||This is due to the breakdown of urea into ammonia|
|Color||Urine will become darker||Due to oxidation or reduction of metabolites|
|Turbidity||This will increase||Due to bacterial growth and crystal precipitation|
|Odor||This will be foul-smelling/increased||Due to bacterial decomposition of urea and ammonia|
|Cast||Decreased or disappeared||These are dissolved|
|Glucose||It is decreased||This is due to glycolysis.|
|Bilirubin||It is decreased, and the color changes from yellow to green.||Bilirubin oxidized to biliverdin.|
|Urobilinogen||It is decreased, and color changes from colorless to orange-red.||Urobilinogen oxidized to urobilin.|
|Acetone (Ketones)||This is decreased||This is due to the evaporation of acetone.|
|Acetoacetic acid||This is decreased||This is converted into acetone and evaporation.|
|Nitrite||This will increase||Due to bacterial production|
|Cells||These may disappear or decrease.||This is due to lysis.|
|Red blood cells||These are lysed||Due to alkaline urine|
|WBC||These will disintegrates||Due to dilute alkaline urine|
|Bacteria||Their number will increase.||Due to bacterial proliferation|
Urine changes without preservation:
|Parameters||Reason for the changes
|Change in color||
|Change in turbidity||
|Change in odor||
|Low pH (false)||
|High pH (false)||
|Destruction of cells or cast||
|Increased number of bacteria||
|Red blood cells||
|White blood cells||
- Preservatives are added to reduce the growth of the bacteria, action of the bacteria, or chemical decomposition.
- Preservatives prevent the precipitation of chemical substances.
- The best option is to keep urine immediately in the fridge after the collection.
- If you add chemical preservatives and immediately keep them in the fridge, is the best option.
- When you do acidification of the urine (24 hours sample) and pH is <3 is useful for the preservation of calcium, steroids, and VMA estimation.
- Sodium bicarbonate (NaHCO3), or sodium hydroxide (NaOH) is used to preserve the estimation of porphyrins, urobilinogen, and uric acid.
Following urine, preservatives are used for various purposes.
- Sodium fluoride.
- Boric acid.
Urine preservatives for 24 hours of urine sample:
|Preservatives for 24 hours urine||Concentrations per volume of urine|
|Boric acid||10 grams/24 hours of urine|
|Acetic acid||50%; 25 mL /24 hours of urine|
|Hydrochloric acid (HCL)||6 mol/L; 30 mL/24 hours of urine|
|Nitric acid (HNO3)||6 mol/L; 15 mL/24 hours of urine|
|Sodium carbonate (Na2CO3)||5 grams/24 hours of urine|