Urine changes When Urine Left at Room Temperature and Without Preservatives

Precautions in the collection of urine:

1. Proper collection and the handling of the urine are important to get accurate results. It depends upon:
   1. Containers used should be clean, dry, and proper for the sample.
   2. Should follow proper collection procedure.
   3. Storage conditions are also important.
   4. A proper preservative is also important to get accurate results.
      1. Disposable inert plastic containers with a secure cap are the best for urine collection.
2. When urine is left in the lab at room temperature for a longer period (maybe over 24 hours), biochemical and microbiological changes occur.
3. For routine urine analysis, freshly voided urine is a better sample than the catheterized sample.
4. Avoid the contamination of urine from the vaginal secretion (discharge) or hemorrhage.
   1. Get the clean voided midstream urine, particularly for the bacteriological examination.
   2. It may be needed to pack the vagina or use the tampoon to avoid vaginal contamination.
5. The best sample to check urine glucose is one voided 2 to 3 hours after the last meal.
   1. This is the exception of the early first-morning sample.
6. The key importance is to check the fresh or suitably preserved urine, usually refrigerated.
   1. Examine urine within 30 minutes of the collection, as the changes (decomposition) start during this time.
   2. Try to examine the urine in the first 1 to 2 hours of collection.
   3. Urine is the best culture media for the growth of bacteria.
   4. If it is delayed, then refrigerate the urine at 4 °C.
7. Urine left at room temperature >2 hours is not acceptable.
8. Urine preservatives are only accepted for 24 hours of urine collection and not for a routine examination.

Urine sample to be rejected:

1. 1. When urine has incorrect preservatives.
   2. When the urine quantity is insufficient.
   3. When urine is not collected with all needed precautions.
   4. When there is a missing or incomplete request form.
   5. When urine has no proper identification.
   6. 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:

1. Urine normally becomes hazy or cloudy, when let at room temperature. This can be reversed by adding few drops of acid.
   1. Vaginal contamination is quite a common cause of cloudy urine in a female patient.
2. The normal color of the urine darkens on standing for longer than 30 minutes, due to oxidation of urobilinogen to urobilin.
3. Red blood cells: These are distorted because of the lack of isotonic solution.
   1. RBCs become crenated or swell, which makes them difficult to recognize.
   2. Finally, RBCs disintegrate.
4. White blood cells: WBCs disintegrate in a hypotonic solution.
5. Cast: These will disintegrate, especially as the urine becomes alkaline, but these casts need acidic urine and solute for their existence in the urine.
6. The alkalinity of urine: Other substance which appears in the acidic urine will disappear in the alkaline urine.
   1. Alkalinity develops because of the growth of the bacteria and the production of ammonia.
7. Bacteria: These will multiply and obscure the various components.
   

   Urine changes when left in the lab

Changes when urine left for a longer period of time 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 to 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 yellow to green.	Bilirubin oxidized to biliverdin.
Urobilinogen	It is decreased, and color changes 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 preservatives:

Characteristics	Reason for the changes
Change in color	Darkened due to: Breakdown or alteration of chromogens Or  other constituents like hemoglobin, homogentisic acid
Change in turbidity	This is due to: Crystal formation. Bacterial growth. Precipitation of amorphous material.
Change in odor	Increased due to: Multiplication of bacterial growth Decomposition. Breakdown of urea to ammonia by bacteria
pH	Increased due to: Breakdown of urea to ammonia by urease producing bacteria Loss of CO2
Low pH (false)	This is due to: The conversion of glucose to acids or alcohol due to bacterial or yeast action.
High pH (false)	This is due to: The breakdown of urea by bacteria that produces ammonia.
Glucose	Decreased due to: Glycolysis By bacterial utilization
False-negative glucose	This is due to: The utilization of glucose by bacteria.
False-positive glucose	This is due to: The contamination of the container.
Ketones	Decreased due to: Volatile nature of ketone bodies Bacterial metabolism
False-negative ketones	This is due to: The breakdown of acetoacetate by bacteria Or the volatility of acetone.
Nitrite	Increased due to: Multiplication of nitrate-reducing bacteria
False-positive nitrite	This is due to: The production of nitrite by bacteria.
False-negative nitrite	This is due to: The conversion of nitrite to nitrogen evaporation.
Bilirubin	Decreased due to: Exposure to light Photo-oxidation to biliverdin
False-negative bilirubin	This is due to: Destruction by light or oxidized to biliverdin
Urobilinogen	Decreased due to: Oxidation to urobilin
False-negative urobilinogen	This is due to: When urine is exposed to light
Amorphous urates/phosphates	Precipitate by refrigeration Increase the turbidity.
Destruction of cells or cast	This is due to: An unstable environment, especially when urine is alkaline.
Increased number of bacteria	This is due to: The multiplication of bacteria when left at room temperature.
Red blood cells	Decreased due to: Disintegration in dilute alkaline urine
White blood cells	Decreased due to: Disintegration in dilute alkaline urine
Casts	Decreased due to: Disintegration in dilute alkaline urine
Bacteria	Bacteria increased because of the multiplication. This results in cloudy urine and changes in the pH.

 

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