A 26-year-old man has had 5 days of nausea, fatigue and dark urine. ALT is 1,620 U/L (reference below 40 U/L), and serum total bilirubin is 2.0 mg/dL [34 µmol/L], of which 1.3 mg/dL [22 µmol/L] is direct (conjugated). A fresh urine kept away from light gives: SG 1.022, pH 6.0, bilirubin pad negative, urobilinogen 3 EU/dL (reference below 1.0 EU/dL), ascorbic acid pad negative. Strip QC is acceptable. An Ictotest on the same urine turns the mat blue-purple within 60 seconds, and its positive and negative controls are acceptable. The best interpretation of these results is:

Bilirubin below the pad's detection limit

A false-positive tablet test from pigment

Unconjugated bilirubin found by the tablet

Bilirubin destroyed by light before the strip

After a crush injury, a patient's urine is strongly positive for blood on the reagent strip, but no red cells are seen on microscopy. The plasma is clear and the serum CK is very high. What is the most likely cause?

Hemoglobinuria from intravascular hemolysis

Hematuria with red cells lysed in dilute urine

The Clinitest tablet detects reducing substances in urine by:

Copper reduction (cupric to cuprous)

Precipitation with sulfosalicylic acid

During a 5-drop Clinitest, the color passes quickly through bright orange and ends dark greenish-brown. This means:

Very high sugar; repeat by the 2-drop method

Only a trace of reducing sugar is present

Sucrose is reacting with the copper reagent

Ascorbic acid has reduced the copper reagent

Chemical examination: confirmatory tests

7 ASCP MLS practice questions on Chemical examination: confirmatory tests, part of Urinalysis and Body Fluids. The first 7 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 · Hard
A 26-year-old man has had 5 days of nausea, fatigue and dark urine. ALT is 1,620 U/L (reference below 40 U/L), and serum total bilirubin is 2.0 mg/dL [34 µmol/L], of which 1.3 mg/dL [22 µmol/L] is direct (conjugated). A fresh urine kept away from light gives: SG 1.022, pH 6.0, bilirubin pad negative, urobilinogen 3 EU/dL (reference below 1.0 EU/dL), ascorbic acid pad negative. Strip QC is acceptable. An Ictotest on the same urine turns the mat blue-purple within 60 seconds, and its positive and negative controls are acceptable. The best interpretation of these results is:
1. AA false-positive tablet test from pigment
2. BUnconjugated bilirubin found by the tablet
3. CBilirubin below the pad's detection limit
4. DBilirubin destroyed by light before the strip
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Answer: C · Bilirubin below the pad's detection limit
The Ictotest uses the same diazo reaction as the strip pad but detects about 0.05 to 0.1 mg/dL of bilirubin, compared with about 0.4 to 0.8 mg/dL for most pads. Early in hepatitis, conjugated bilirubin can be present in the urine below the pad's limit, so the more sensitive tablet test is positive. The raised direct bilirubin and urobilinogen fit hepatocellular injury, which lets conjugated bilirubin back into the blood and then into the urine. The tablet test is also less affected by interfering substances than the pad. The urine bilirubin should be reported as positive by the Ictotest.
- A: A true positive is blue to purple, pigments give other colors, and the controls are acceptable.
- B: Unconjugated bilirubin is bound to albumin, is not filtered, and does not appear in urine.
- D: The urine was protected from light, and photo-oxidation would have made the Ictotest negative too.
Question 2 · Hard
After a crush injury, a patient's urine is strongly positive for blood on the reagent strip, but no red cells are seen on microscopy. The plasma is clear and the serum CK is very high. What is the most likely cause?
1. AAscorbic acid interference
2. BHemoglobinuria from intravascular hemolysis
3. CMyoglobinuria
4. DHematuria with red cells lysed in dilute urine
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Answer: C · Myoglobinuria
The strip blood pad detects the peroxidase activity of both hemoglobin and myoglobin. Myoglobin from damaged muscle is small and cleared quickly by the kidney, so the plasma stays clear. Hemoglobin from hemolysis colors the plasma pink and lowers haptoglobin. A very high CK after crush injury fits rhabdomyolysis, which risks acute kidney injury.
- A: Ascorbic acid gives false-negative blood results, not false positives.
- B: Hemoglobinuria would come with pink plasma and evidence of hemolysis.
- D: Lysed red cells can explain a positive pad without cells, but the clear plasma and high CK point to muscle.
Question 3 · Easy
The Clinitest tablet detects reducing substances in urine by:
1. ACopper reduction (cupric to cuprous)
2. BPrecipitation with sulfosalicylic acid
3. CDiazo coupling in acid
4. DGlucose oxidase and peroxidase
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Answer: A · Copper reduction (cupric to cuprous)
The tablet contains copper sulfate, sodium hydroxide, sodium carbonate and sodium citrate, and the sodium hydroxide produces heat as it dissolves. Reducing substances convert blue cupric sulfate to cuprous oxide, giving colors from blue (negative) through green and yellow to orange-red. Any reducing sugar reacts, including glucose, galactose, lactose and fructose, but not sucrose. This makes it useful for finding sugars that the glucose oxidase pad misses.
- B: Acid precipitation is the SSA protein test.
- C: Diazo coupling is the bilirubin reaction.
- D: Glucose oxidase is specific for glucose and is the strip method.
Question 4 · Easy
In the Ictotest for urine bilirubin, which color on the mat within 60 seconds is a positive result?
1. AA blue-to-purple color
2. BA pink-to-red color
3. CA yellow-brown color
4. DA bright green color
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Answer: A · A blue-to-purple color
Urine is placed on an absorbent mat that holds bilirubin on its surface, and the tablet's diazonium salt couples with bilirubin to form a blue-to-purple color. Pink or red colors are read as negative. The Ictotest is more sensitive than the strip pad and less affected by interfering substances, so it is used to confirm a doubtful strip result. Like the strip, it needs a fresh specimen protected from light.
- B: Pink or red colors are read as negative.
- C: A yellow-brown stain is the urine itself, not the reaction product.
- D: A green color is not the endpoint of the diazo reaction.
Question 5 · Medium
During a 5-drop Clinitest, the color passes quickly through bright orange and ends dark greenish-brown. This means:
1. AOnly a trace of reducing sugar is present
2. BVery high sugar; repeat by the 2-drop method
3. CSucrose is reacting with the copper reagent
4. DAscorbic acid has reduced the copper reagent
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Answer: B · Very high sugar; repeat by the 2-drop method
When the sugar concentration is above about 2 g/dL, the color passes through orange and then turns back to a dark greenish-brown: the pass-through phenomenon. If only the final color is read, a very high result can be mistaken for a low one. The reaction must be watched throughout and, if pass-through occurs, repeated by the 2-drop method, which reads up to 5 g/dL. Sucrose is not a reducing sugar and does not react.
- A: Reading only the end color mistakes a very high result for a low one.
- C: Sucrose is a non-reducing sugar and does not react.
- D: Ascorbic acid can give a positive result but does not cause pass-through.
Question 6 · Medium
A 68-year-old with bone pain and anemia has a negative protein pad, but the SSA test is 2+. Which protein is most likely present?
1. AHemoglobin
2. BImmunoglobulin light chains
3. CAlbumin
4. DUromodulin (Tamm-Horsfall protein)
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Question 7 · Hard
A patient had a CT scan with iodinated contrast earlier today. Urine: pH 6.0, protein pad negative, SSA 2+, strip specific gravity 1.015, refractometer specific gravity 1.045. What best explains the SSA result?
1. AAlbumin below the pad's detection limit
2. BIodinated contrast medium in the urine
3. CBence Jones protein from myeloma
4. DHighly buffered alkaline urine
Answer and explanation in LearnFree account

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Chemical examination: confirmatory tests

After a crush injury, a patient's urine is strongly positive for blood on the reagent strip, but no red cells are seen on microscopy. The plasma is clear and the serum CK is very high. What is the most likely cause?

The Clinitest tablet detects reducing substances in urine by:

In the Ictotest for urine bilirubin, which color on the mat within 60 seconds is a positive result?

During a 5-drop Clinitest, the color passes quickly through bright orange and ends dark greenish-brown. This means:

A 68-year-old with bone pain and anemia has a negative protein pad, but the SSA test is 2+. Which protein is most likely present?

A patient had a CT scan with iodinated contrast earlier today. Urine: pH 6.0, protein pad negative, SSA 2+, strip specific gravity 1.015, refractometer specific gravity 1.045. What best explains the SSA result?