Which changes occur in an unpreserved urine sample left at room temperature for several hours?

pH and bacteria rise, glucose falls, cells and casts degrade

Casts and cells increase in number as protein precipitates

pH falls as bacteria make acid from the glucose present

Glucose rises as cells and casts break down

A patient begins a 24-hour urine at 07:00 by passing the 07:00 urine into the container, and ends with the 07:00 urine the next morning. The 24-hour excretion results will be:

Falsely high, from one extra void

Falsely low, from one missing void

Accurate, as the volume is measured

Falsely low, from dilution of the pool

Refrigerating a urine at 2-8 °C slows bacterial growth, but a common drawback is that it:

Precipitates amorphous urates and phosphates

Raises the pH through bacterial urease

Lowers glucose through glycolysis

Dissolves hyaline casts and lyses cells

Urine specimen collection and handling

9 DOH Abu Dhabi (HAAD) lab licensing practice questions on Urine specimen collection and handling, part of Urinalysis and Body Fluids. The first 9 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Easy
Which changes occur in an unpreserved urine sample left at room temperature for several hours?
1. ACasts and cells increase in number as protein precipitates
2. BpH falls as bacteria make acid from the glucose present
3. CpH and bacteria rise, glucose falls, cells and casts degrade
4. DGlucose rises as cells and casts break down
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Answer: C · pH and bacteria rise, glucose falls, cells and casts degrade
Bacteria multiply in warm urine and break down urea to ammonia, which raises the pH. They also use glucose, lowering it. Cells and casts disintegrate, especially in alkaline, dilute urine. Samples should be tested within about two hours or refrigerated.
- A: Casts break down; they do not increase.
- B: Bacterial breakdown of urea makes urine more alkaline, not acidic.
- D: Bacteria consume glucose, so it falls.
Question 2 · Easy
If it is not refrigerated or preserved, a urine for routine urinalysis should be tested within:
1. A6 hours of collection
2. B12 hours of collection
3. C24 hours of collection
4. D2 hours of collection
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Answer: D · 2 hours of collection
CLSI urinalysis guidance asks for testing within 2 hours of collection, or refrigeration or a suitable preservative if testing will be delayed. At room temperature, bacteria multiply and split urea to ammonia, raising the pH, and cells and casts break down, especially in dilute alkaline urine. Recording the collection time on the request makes this check possible.
- A: By 6 hours, bacterial growth and cell breakdown can already change the results.
- B: 12 hours is far too long for an unpreserved specimen at room temperature.
- C: A 24-hour delay at room temperature would make most routine results unreliable.
Question 3 · Medium
A patient begins a 24-hour urine at 07:00 by passing the 07:00 urine into the container, and ends with the 07:00 urine the next morning. The 24-hour excretion results will be:
1. AFalsely low, from one missing void
2. BFalsely high, from one extra void
3. CAccurate, as the volume is measured
4. DFalsely low, from dilution of the pool
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Answer: B · Falsely high, from one extra void
A timed collection must start with an empty bladder: the patient voids and discards the urine at the start time, collects everything afterwards, and adds a final void at the end time. Here the first void holds urine made before the collection began, so the container holds more than 24 hours of urine. Daily excretion of protein, creatinine or hormones is overestimated. The fix is to recollect with clear written instructions.
- A: Nothing was missed; the extra urine came from before the start time.
- C: Measuring the volume does not correct for urine formed outside the 24 hours.
- D: Concentration may change, but the total amount excreted is what is overstated.
Question 4 · Medium
Refrigerating a urine at 2-8 °C slows bacterial growth, but a common drawback is that it:
1. APrecipitates amorphous urates and phosphates
2. BRaises the pH through bacterial urease
3. CLowers glucose through glycolysis
4. DDissolves hyaline casts and lyses cells
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Answer: A · Precipitates amorphous urates and phosphates
Cold lowers the solubility of urates and phosphates, so amorphous material can precipitate and hide the sediment. A refrigerated sample should return to room temperature before strip testing, because cold slows the enzyme reactions on the pads. Gentle warming dissolves urates, and dilute acetic acid dissolves phosphates, if the sediment must be cleared. Refrigeration is still the most widely used way to preserve a routine urine.
- B: Refrigeration slows bacterial growth and urease activity; it does not raise the pH.
- C: Glycolysis by cells and bacteria is slowed, not speeded, by cold.
- D: Cell lysis and cast breakdown happen at room temperature and in alkaline urine; cold slows them.
Question 5 · Easy
Which way of obtaining urine avoids the urethra and skin altogether, so that the sample is acceptable for anaerobic culture?
1. AMidstream clean-catch
2. BIndwelling catheter port
3. CSingle straight catheter
4. DSuprapubic aspiration
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Answer: D · Suprapubic aspiration
In suprapubic aspiration a needle is passed through the abdominal wall directly into a full bladder, so the urine never passes the urethra. It is the only urine acceptable for anaerobic culture, and any organism grown is significant. It is used mainly in infants and when voided or catheter samples give doubtful results.
- A: A midstream sample passes the urethra and can contain skin and urethral flora.
- B: Catheter-port urine reflects organisms colonizing the catheter, not sterile bladder urine.
- C: A catheter passes through the urethra and can carry urethral organisms into the bladder.
Question 6 · Medium
Formalin added to a urine specimen is a good preservative for:
1. ACells and casts in the sediment
2. BBacteria for urine culture
3. CUrobilinogen and bilirubin
4. DThe reagent strip glucose test
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Question 7 · Medium
A timed 2-hour urine for urobilinogen is usually collected in the early afternoon. Why?
1. ABacteria are fewest in afternoon urine
2. BUrine is most concentrated in the afternoon
3. CUrobilinogen is unstable in morning urine
4. DUrobilinogen excretion peaks at that time
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Question 8 · Hard
A urine for protein was started at 07:00 with an empty bladder and ended with a final void at 10:00 the next day. Volume 2,700 mL; protein 0.40 g/L. What is the protein excretion expressed per 24 hours?
1. A0.96 g/24 h
2. B1.08 g/24 h
3. C0.40 g/24 h
4. D1.22 g/24 h
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Question 9 · Easy
A first morning urine is preferred for routine screening mainly because it is:
1. AThe most dilute urine of the day
2. BThe most concentrated urine of the day
3. CFree of bacteria and epithelial cells
4. DCollected after the patient has eaten
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Urine specimen collection and handling

Which changes occur in an unpreserved urine sample left at room temperature for several hours?

If it is not refrigerated or preserved, a urine for routine urinalysis should be tested within:

A patient begins a 24-hour urine at 07:00 by passing the 07:00 urine into the container, and ends with the 07:00 urine the next morning. The 24-hour excretion results will be:

Refrigerating a urine at 2-8 °C slows bacterial growth, but a common drawback is that it:

Which way of obtaining urine avoids the urethra and skin altogether, so that the sample is acceptable for anaerobic culture?

Formalin added to a urine specimen is a good preservative for:

A timed 2-hour urine for urobilinogen is usually collected in the early afternoon. Why?

A urine for protein was started at 07:00 with an empty bladder and ended with a final void at 10:00 the next day. Volume 2,700 mL; protein 0.40 g/L. What is the protein excretion expressed per 24 hours?

A first morning urine is preferred for routine screening mainly because it is: