A 31-year-old woman has severe abdominal pain, vomiting, constipation and weakness of both arms after several days of fasting. The laboratory is comparing two strip brands and tests her fresh urine on both at the same time. Strip A, whose urobilinogen pad uses p-dimethylaminobenzaldehyde (Ehrlich reagent), reads 8 EU/dL [about 135 µmol/L]. Strip B, whose urobilinogen pad uses a diazonium salt, reads 0.2 EU/dL [about 3.4 µmol/L]; the reference is below 1.0 EU/dL. Bilirubin is negative on both strips, serum bilirubin and ALT are normal, and her hemoglobin is normal with no sign of hemolysis. What best explains the different urobilinogen results?

Porphobilinogen reacting with the Ehrlich pad

Urobilinogen oxidized before strip B was read

More urobilinogen from hidden hemolysis

Bilirubin blocking the diazonium pad reaction

A 4-year-old girl with fever and urgency is passing small amounts of urine every 30 to 45 minutes. A clean-catch urine is tested within 15 minutes of collection: SG 1.008, pH 6.0, leukocyte esterase 2+, nitrite negative, blood trace, ascorbic acid screen negative. Sediment: 25-50 WBC/HPF and many bacteria, mostly rods. Culture grows more than 10^5 CFU/mL of Escherichia coli. Strip controls were acceptable, and she eats a normal diet that includes vegetables. The most likely reason for the negative nitrite result is:

Urine stayed too briefly in the bladder

Escherichia coli lacks nitrate reductase

The urine was tested too soon after collection

A 52-year-old woman with type 2 diabetes has dysuria. A fresh midstream urine tested at room temperature within 30 minutes gives: SG 1.016, pH 6.0, glucose negative, blood negative, nitrite negative, leukocyte esterase moderate. Sediment: 15-20 RBC/HPF, 20-30 WBC/HPF and many rods. Plasma glucose drawn at the same visit is 310 mg/dL [17.2 mmol/L], her kidney function is normal, and the culture later grows more than 10^5 CFU/mL of Escherichia coli. Strip QC this morning was acceptable. For a week she has been taking a high-dose vitamin supplement for a cold. The most likely cause of the negative pads is:

Ascorbic acid from the supplement

A urine too concentrated for the pads

Reagent strips damaged by moisture

Glucose consumed by the bacteria

A 78-year-old man with a long-term catheter and recurrent Proteus mirabilis infections has a urine collected from a newly placed catheter and tested within 20 minutes on a fully automated strip analyzer. Results: SG 1.014, pH 9.0, protein 1+ (30 mg/dL [0.3 g/L]), blood negative, nitrite positive, leukocyte esterase 2+. The sediment shows many WBCs, bacteria and coffin-lid crystals. A sulfosalicylic acid (SSA) test on the centrifuged supernatant is negative. He has had no recent imaging, and no antiseptic was used on the catheter. The most likely explanation for the protein pad result is:

Alkaline urine overriding the pad's acid buffer

Albumin below the detection limit of SSA

Light chains detected by the pad only

Contrast medium reacting with the pad

Chemical examination: reagent strips

38 ASCP MLS practice questions on Chemical examination: reagent strips, part of Urinalysis and Body Fluids. The first 25 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 31-year-old woman has severe abdominal pain, vomiting, constipation and weakness of both arms after several days of fasting. The laboratory is comparing two strip brands and tests her fresh urine on both at the same time. Strip A, whose urobilinogen pad uses p-dimethylaminobenzaldehyde (Ehrlich reagent), reads 8 EU/dL [about 135 µmol/L]. Strip B, whose urobilinogen pad uses a diazonium salt, reads 0.2 EU/dL [about 3.4 µmol/L]; the reference is below 1.0 EU/dL. Bilirubin is negative on both strips, serum bilirubin and ALT are normal, and her hemoglobin is normal with no sign of hemolysis. What best explains the different urobilinogen results?
1. APorphobilinogen reacting with the Ehrlich pad
2. BUrobilinogen oxidized before strip B was read
3. CMore urobilinogen from hidden hemolysis
4. DBilirubin blocking the diazonium pad reaction
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Answer: A · Porphobilinogen reacting with the Ehrlich pad
The Ehrlich reagent reacts with urobilinogen but also with other Ehrlich-reactive compounds, including porphobilinogen. A diazonium (azo-coupling) urobilinogen pad is more specific for urobilinogen and does not react with porphobilinogen. A high Ehrlich result with a normal diazonium result, normal bilirubin and no hemolysis therefore points to an Ehrlich-reactive substance other than urobilinogen. With abdominal pain and weakness after fasting, that substance is most likely porphobilinogen from an attack of acute intermittent porphyria. Neither strip is a reliable test for porphobilinogen, so a specific urine porphobilinogen test should be requested at once.
- B: Both strips were dipped at the same time, so oxidation cannot explain the difference between them.
- C: Hemolysis raises true urobilinogen, which the specific diazonium pad would also detect, and there is no hemolysis.
- D: Bilirubin is negative on both strips, so it cannot be interfering.
Question 2 · Hard
A 4-year-old girl with fever and urgency is passing small amounts of urine every 30 to 45 minutes. A clean-catch urine is tested within 15 minutes of collection: SG 1.008, pH 6.0, leukocyte esterase 2+, nitrite negative, blood trace, ascorbic acid screen negative. Sediment: 25-50 WBC/HPF and many bacteria, mostly rods. Culture grows more than 10^5 CFU/mL of Escherichia coli. Strip controls were acceptable, and she eats a normal diet that includes vegetables. The most likely reason for the negative nitrite result is:
1. AToo little nitrate in her diet
2. BEscherichia coli lacks nitrate reductase
3. CUrine stayed too briefly in the bladder
4. DThe urine was tested too soon after collection
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Answer: C · Urine stayed too briefly in the bladder
Gram-negative rods such as E. coli reduce dietary nitrate to nitrite, but they need about 4 hours in contact with bladder urine to make a detectable amount. A child voiding every 30 to 45 minutes gives the bacteria too little time, and the dilute urine (SG 1.008) lowers the nitrite concentration further. Ascorbic acid, faulty strips and a lack of dietary nitrate have all been excluded. This is why a first morning urine, or one held in the bladder for at least 4 hours, is preferred for nitrite screening. A negative nitrite never rules out infection when the esterase, microscopy and culture are positive.
- A: Her normal diet with vegetables supplies enough nitrate.
- B: E. coli and most other Enterobacterales reduce nitrate to nitrite.
- D: Prompt testing is correct; nitrite forms in the bladder, and delay causes false positives, not negatives.
Question 3 · Hard
A 52-year-old woman with type 2 diabetes has dysuria. A fresh midstream urine tested at room temperature within 30 minutes gives: SG 1.016, pH 6.0, glucose negative, blood negative, nitrite negative, leukocyte esterase moderate. Sediment: 15-20 RBC/HPF, 20-30 WBC/HPF and many rods. Plasma glucose drawn at the same visit is 310 mg/dL [17.2 mmol/L], her kidney function is normal, and the culture later grows more than 10^5 CFU/mL of Escherichia coli. Strip QC this morning was acceptable. For a week she has been taking a high-dose vitamin supplement for a cold. The most likely cause of the negative pads is:
1. AA urine too concentrated for the pads
2. BAscorbic acid from the supplement
3. CReagent strips damaged by moisture
4. DGlucose consumed by the bacteria
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Answer: B · Ascorbic acid from the supplement
Three pads are negative despite clear evidence of their analytes: glucose should spill into the urine at a plasma level of 310 mg/dL, red cells are seen, and E. coli normally makes nitrite. Ascorbic acid is a strong reducing agent; it uses up the peroxide or reduces the oxidized chromogen on the glucose and blood pads and interferes with the diazo reaction of the nitrite pad. High-dose vitamin C can put enough ascorbic acid in the urine to cause all three false negatives. The acceptable QC, the fresh specimen and the normal specific gravity rule out the other explanations. Many laboratories use an ascorbic acid pad or ask about supplements, and retest about 24 hours after the last dose.
- A: A specific gravity of 1.016 is not high enough to suppress the pads.
- C: Strip QC was acceptable this morning, so the strips are working.
- D: A specimen tested within 30 minutes has not lost this much glucose, and glycolysis would not explain the blood and nitrite pads.
Question 4 · Hard
A 78-year-old man with a long-term catheter and recurrent Proteus mirabilis infections has a urine collected from a newly placed catheter and tested within 20 minutes on a fully automated strip analyzer. Results: SG 1.014, pH 9.0, protein 1+ (30 mg/dL [0.3 g/L]), blood negative, nitrite positive, leukocyte esterase 2+. The sediment shows many WBCs, bacteria and coffin-lid crystals. A sulfosalicylic acid (SSA) test on the centrifuged supernatant is negative. He has had no recent imaging, and no antiseptic was used on the catheter. The most likely explanation for the protein pad result is:
1. AAlkaline urine overriding the pad's acid buffer
2. BAlbumin below the detection limit of SSA
3. CLight chains detected by the pad only
4. DContrast medium reacting with the pad
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Answer: A · Alkaline urine overriding the pad's acid buffer
The protein pad works by the protein error of indicators: at a pH held near 3 by the pad's buffer, protein accepts hydrogen ions from an indicator such as tetrabromphenol blue, and the color changes. A highly buffered alkaline urine, such as the pH 9.0 urine produced by urease-forming Proteus, can override the buffer, so the indicator changes color without protein. SSA precipitates protein in acid and is negative, which shows that the pad result is false. The struvite (triple phosphate) crystals fit the urease-driven alkaline urine. The protein result should be reported with a comment or measured by a method not affected by urine pH.
- B: SSA detects albumin at lower levels than the pad, so albumin seen only by the pad does not fit.
- C: Light chains react poorly with the pad and precipitate with SSA, the opposite of this pattern.
- D: Contrast media cause false-positive SSA results, not pad results, and he has had no imaging.
Question 5 · Medium
Refer to the protein results shown for four urines. Which urine's results point to a protein other than albumin, such as immunoglobulin light chains?
Figure: MedExams
1. AUrine 3
2. BUrine 2
3. CUrine 1
4. DUrine 4
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Answer: B · Urine 2
The strip protein pad relies on the protein error of indicators and is far more sensitive to albumin than to globulins or light chains. Sulfosalicylic acid precipitates all proteins, so a negative pad with a 3+ SSA in urine 2 means a non-albumin protein is present. Urine 3 is the reverse: a pH of 9.0 overcomes the pad's buffer and gives a false-positive strip, while SSA is negative. Urine 2 should go on to protein electrophoresis and immunofixation for a monoclonal light chain.
- A: Urine 3 is a false-positive strip from highly alkaline urine; SSA is negative.
- C: Urine 1 agrees on both tests, which fits albumin.
- D: Urine 4 shows a small amount of protein that both tests agree on.
Question 6 · Easy
The reagent strip results shown are from a random urine. Judged against the reference values, the abnormal result is:
Figure: MedExams
1. ASpecific gravity 1.030
2. BpH 7.5
3. CUrobilinogen 0.2 EU/dL
4. DProtein 30 mg/dL (1+)
Answer and explanation in LearnFree account
Question 7 · Medium
The protein pad on a urine reagent strip is most sensitive to which protein?
1. AImmunoglobulin G
2. BAlbumin
3. CBence Jones protein (free light chains)
4. DHemoglobin
Answer and explanation in LearnFree account
Question 8 · Hard
A woman brings a urine collected at home in a jar she had just cleaned. Glucose is 250 mg/dL [13.9 mmol/L] and blood is large with an even color, but no red cells are seen; her fasting serum glucose is 88 mg/dL [4.9 mmol/L]. What is the most likely cause?
1. AAn oxidizing cleaner left in the jar
2. BAscorbic acid left in the jar
3. CRenal glycosuria with hemoglobinuria
4. DMyoglobinuria with diabetes mellitus
Answer and explanation in LearnFree account
Question 9 · Hard
A patient receiving ifosfamide with mesna has a moderate urine ketone reaction. Serum glucose is 92 mg/dL [5.1 mmol/L], serum β-hydroxybutyrate is normal, and she is eating normally. What most likely explains the ketone result?
1. AEarly diabetic ketoacidosis
2. BStarvation ketosis from vomiting
3. CIfosfamide-induced tubular damage
4. DFree sulfhydryl groups in mesna
Answer and explanation in LearnFree account
Question 10 · Medium
A urine from a jaundiced patient sits on a sunny bench for 3 hours and then gives a negative bilirubin pad. The most likely reason is:
1. ABinding of bilirubin to albumin in the urine
2. BPhoto-oxidation of bilirubin to biliverdin
3. CPrecipitation of bilirubin as crystals
4. DBacterial conversion of bilirubin to urobilinogen
Answer and explanation in LearnFree account
Question 11 · Easy
The two indicators used on the reagent strip pH pad are:
1. ADiazonium salt and acid buffer
2. BTetrabromphenol blue and citrate
3. CMethyl red and bromthymol blue
4. DSodium nitroprusside and glycine
Answer and explanation in LearnFree account
Question 12 · Hard
A kidney transplant recipient's fresh urine shows 15-20 WBC/HPF, mostly small cells with a single round nucleus and scant cytoplasm. Leukocyte esterase, read at 2 minutes, is negative, and glucose is negative. What best explains the negative esterase?
1. ALymphocytes lack the esterase the pad detects
2. BThe pad was read too early to show color
3. CThe white cells lysed before the strip was dipped
4. DGlucose in the urine inhibited the reaction
Answer and explanation in LearnFree account
Question 13 · Hard
A woman with dysuria started a medicine two days ago. Her fresh urine is thick and orange; the nitrite and bilirubin pads show unusual positive colors, microscopy shows no bacteria or WBCs, and serum bilirubin is normal. The most likely cause of the pad results is:
1. AInfection with a nitrate-reducing organism
2. BConjugated bilirubin from liver disease
3. CBacterial growth in a stored specimen
4. DPigment from phenazopyridine
Answer and explanation in LearnFree account
Question 14 · Easy
The glucose pad of a urine reagent strip is based on:
1. ACopper reduction in alkali
2. BGlucose oxidase and peroxidase
3. CThe protein error of indicators
4. DHexokinase and NADPH formation
Answer and explanation in LearnFree account
Question 15 · Hard
A man with type 2 diabetes has a negative protein pad at every visit. His urine albumin is 5 mg/dL [50 mg/L] and his albumin-to-creatinine ratio is 60 mg/g [6.8 mg/mmol]. The best explanation is:
1. AThe protein pad detects globulins but not albumin
2. BHis albumin is below the protein pad's detection limit
3. CAlkaline urine suppresses the protein pad
4. DHigh urine glucose inhibits the protein pad
Answer and explanation in LearnFree account
Question 16 · Hard
An outpatient urine reached the laboratory after 7 hours at room temperature. Nitrite is positive and leukocyte esterase negative, microscopy shows many bacteria but no WBCs, and culture grows three organisms. The best interpretation is:
1. AEarly infection before white cells appear
2. BUpper urinary tract infection (pyelonephritis)
3. CPigment interference with the nitrite pad
4. DBacteria multiplied in the unrefrigerated specimen
Answer and explanation in LearnFree account
Question 17 · Medium
The reagent strip specific gravity pad responds to:
1. AAll dissolved solutes, including glucose
2. BIons that release H+ from a polyelectrolyte
3. CFreezing point depression of the urine
4. DThe refractive index of the urine
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Question 18 · Hard
A visually read strip shows a specific gravity of 1.015 on a urine with pH 7.5. After the manufacturer's correction for alkaline urine, the specific gravity to report is:
1. A1.015
2. B1.010
3. C1.020
4. D1.025
Answer and explanation in LearnFree account
Question 19 · Hard
First specimen: SG 1.004, pH 8.0, blood moderate with an even color, nitrite and leukocyte esterase negative, no red cells seen; plasma is clear, and serum CK and haptoglobin are normal. Next morning: SG 1.022, pH 6.0, speckled blood pad, 10-15 RBC/HPF. The first result is best explained by:
1. AMyoglobin from muscle injury
2. BBacterial peroxidases from a urinary infection
3. CRed cells lysing in dilute alkaline urine
4. DHemoglobin from intravascular hemolysis
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Question 20 · Hard
A jaundiced patient has urine bilirubin negative, urine urobilinogen 8 EU/dL, and serum total bilirubin 4.0 mg/dL [68 µmol/L], mostly unconjugated. Which condition fits best?
1. ADubin-Johnson syndrome
2. BHemolytic anemia
3. CBile duct obstruction
4. DAcute viral hepatitis
Answer and explanation in LearnFree account
Question 21 · Medium
Large amounts of ascorbic acid in urine can cause false-negative results on which pair of pads?
1. AGlucose and blood
2. BKetones and specific gravity
3. CProtein and specific gravity
4. DpH and protein
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Question 22 · Hard
A urine collected after the perineum was cleaned with a chlorhexidine wipe gives protein pad 2+, pH 6.0 and a negative SSA test. What is the most likely explanation?
1. AOrthostatic proteinuria
2. BAntiseptic in the specimen
3. CBence Jones proteinuria
4. DHighly buffered alkaline urine
Answer and explanation in LearnFree account
Question 23 · Medium
A random urine has a reagent strip pH of 9.0. What is the most likely explanation?
1. ABacterial urease in an old specimen
2. BMetabolic alkalosis from vomiting
3. CA strict vegetarian (alkaline-ash) diet
4. DDistal renal tubular acidosis
Answer and explanation in LearnFree account
Question 24 · Easy
How should an opened bottle of urine reagent strips be stored?
1. AIn the freezer until the next use
2. BTightly capped with its desiccant at room temperature
3. CUncapped on the bench for quick access
4. DIn a refrigerator at 2-8 °C, tightly capped
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Question 25 · Hard
A technologist dips a strip into the top of a urine that has stood for 40 minutes. Blood and leukocyte esterase are negative, but the sediment from the mixed specimen shows 20-30 RBC/HPF and 10-15 WBC/HPF. The most likely cause is:
1. AThe pads were read later than directed
2. BThe leukocytes present are all lymphocytes
3. CFormalin was added as a preservative
4. DThe specimen was not mixed before dipping
Answer and explanation in LearnFree account

13 more Chemical examination: reagent strips questions

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Chemical examination: reagent strips

Refer to the protein results shown for four urines. Which urine's results point to a protein other than albumin, such as immunoglobulin light chains?

The reagent strip results shown are from a random urine. Judged against the reference values, the abnormal result is:

The protein pad on a urine reagent strip is most sensitive to which protein?

A woman brings a urine collected at home in a jar she had just cleaned. Glucose is 250 mg/dL [13.9 mmol/L] and blood is large with an even color, but no red cells are seen; her fasting serum glucose is 88 mg/dL [4.9 mmol/L]. What is the most likely cause?

A patient receiving ifosfamide with mesna has a moderate urine ketone reaction. Serum glucose is 92 mg/dL [5.1 mmol/L], serum β-hydroxybutyrate is normal, and she is eating normally. What most likely explains the ketone result?

A urine from a jaundiced patient sits on a sunny bench for 3 hours and then gives a negative bilirubin pad. The most likely reason is:

The two indicators used on the reagent strip pH pad are:

A kidney transplant recipient's fresh urine shows 15-20 WBC/HPF, mostly small cells with a single round nucleus and scant cytoplasm. Leukocyte esterase, read at 2 minutes, is negative, and glucose is negative. What best explains the negative esterase?

A woman with dysuria started a medicine two days ago. Her fresh urine is thick and orange; the nitrite and bilirubin pads show unusual positive colors, microscopy shows no bacteria or WBCs, and serum bilirubin is normal. The most likely cause of the pad results is:

The glucose pad of a urine reagent strip is based on:

A man with type 2 diabetes has a negative protein pad at every visit. His urine albumin is 5 mg/dL [50 mg/L] and his albumin-to-creatinine ratio is 60 mg/g [6.8 mg/mmol]. The best explanation is:

An outpatient urine reached the laboratory after 7 hours at room temperature. Nitrite is positive and leukocyte esterase negative, microscopy shows many bacteria but no WBCs, and culture grows three organisms. The best interpretation is:

The reagent strip specific gravity pad responds to:

A visually read strip shows a specific gravity of 1.015 on a urine with pH 7.5. After the manufacturer's correction for alkaline urine, the specific gravity to report is:

First specimen: SG 1.004, pH 8.0, blood moderate with an even color, nitrite and leukocyte esterase negative, no red cells seen; plasma is clear, and serum CK and haptoglobin are normal. Next morning: SG 1.022, pH 6.0, speckled blood pad, 10-15 RBC/HPF. The first result is best explained by:

A jaundiced patient has urine bilirubin negative, urine urobilinogen 8 EU/dL, and serum total bilirubin 4.0 mg/dL [68 µmol/L], mostly unconjugated. Which condition fits best?

Large amounts of ascorbic acid in urine can cause false-negative results on which pair of pads?

A urine collected after the perineum was cleaned with a chlorhexidine wipe gives protein pad 2+, pH 6.0 and a negative SSA test. What is the most likely explanation?

A random urine has a reagent strip pH of 9.0. What is the most likely explanation?

How should an opened bottle of urine reagent strips be stored?

A technologist dips a strip into the top of a urine that has stood for 40 minutes. Blood and leukocyte esterase are negative, but the sediment from the mixed specimen shows 20-30 RBC/HPF and 10-15 WBC/HPF. The most likely cause is: