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The reagent strip: protein and glucose

18 min

Skills you'll build4 skills
  • Perform urine reagent strip testing with the specified read times and quality checks
  • Recognize the protein pad's albumin selectivity and its limits for nonalbumin protein
  • Choose a quantitative albumin-to-creatinine ratio to follow up a urine albumin screen
  • Tell which sugars the glucose oxidase pad detects and which need copper reduction

At the bench: Read urine chemistry and perform the indicated confirmation

Try first

Try first

To save time, a laboratory professional reads every pad of a manual urine strip at 60 seconds. On a strip whose leukocyte esterase pad is labeled for 120 seconds, what happens to that pad?

Keep going to see the reasoning.

Right. Keep going to follow the reasoning.

Keep going to see the reasoning.

Keep going to see the reasoning.

Get the idea

Use the explanation to check your first decision.

Read each pad at its own time

  1. Check the strip lot, expiration date, pad appearance and control results.
  2. Use fresh, well-mixed urine at room temperature.
  3. Dip every pad, withdraw the strip at once and start timing as it leaves the urine. Remove excess urine as the product instructions specify.
  4. Read each pad at its stated time, by eye against the chart or in the validated reader.1

On one common strip, read times run from 30 seconds for glucose and bilirubin to 120 seconds for leukocyte esterase. A color read outside its window has no validated meaning.2

The protein pad

The protein pad works by the protein error of indicators, and albumin gives the strongest color. Globulins and immunoglobulin light chains can be present with a weak or negative pad. A very dilute urine can contain clinically important albumin below the pad's detection limit. Highly alkaline or buffered urine, some disinfectants and a long dip can make the pad falsely positive.1,2

Sulfosalicylic acid (SSA) precipitates a wider range of proteins, light chains included. A strong SSA reaction with a weak pad calls for quantitative protein and electrophoresis. Contrast media can also cloud SSA.4

Albumin screens and the UACR

Albumin-sensitive strips report product-specific screening categories. The urine albumin-to-creatinine ratio (UACR) classifies albuminuria: A1 below 30 mg/g, A2 30 to 300 mg/g, A3 above 300 mg/g.3

UACR (mg/g) = urine albumin (mg/dL) ÷ urine creatinine (mg/dL) × 1,000

A random UACR of 30 mg/g or more is confirmed on a first-morning specimen when feasible. Exercise, fever, infection, menstruation and marked hyperglycemia raise it for a short time. Chronic kidney disease needs an abnormality that persists for at least 3 months.3

The glucose pad

Glucose oxidase turns glucose into gluconic acid and hydrogen peroxide, and peroxidase uses the peroxide to color a chromogen. Galactose, fructose and lactose leave the pad negative. A copper-reduction tablet detects reducing sugars in general, and sucrose is nonreducing. Ascorbic acid and delayed testing can lower the glucose pad.1

Follow the bench demonstration

Sources for this step
References
  1. Kouri TT, Hofmann W, Falbo R, et al. The EFLM European urinalysis guideline 2023. Clin Chem Lab Med. 2024;62(9):1653-1786. doi:10.1515/cclm-2024-0070
  2. Siemens Healthineers. Multistix 10 SG Reagent Strips: Instructions for Use. 11306392 Rev A; 2017. Accessed September 27, 2026. https://doclib.siemens-healthineers.com/rest/v1/view?document-id=401929
  3. Kidney Disease: Improving Global Outcomes CKD Work Group. KDIGO 2024 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney Int. 2024;105(4S):S117-S314. doi:10.1016/j.kint.2023.10.018
  4. Strasinger SK, Di Lorenzo MS. Urinalysis and Body Fluids. 7th ed. F.A. Davis; 2021.

Watch one

Read each decision and its explanation.

Gordon Agar, 58, has type 2 diabetes. An albumin-sensitive strip on his random urine reads positive, and his physician orders a quantitative ratio on the same urine.

What does the laboratory report, and what does a single result show?

TestResultReference intervalFlag
Urine albumin4.2 mg/dL
Urine creatinine60 mg/dL
Nitrite, stripNegativeNegativeNegative
Leukocyte esterase, stripNegativeNegativeNegative

Specimen: Not measured on urine. Random urine, collected 10:40

  1. Treat the strip as a screen: the positive result starts the workup and does not classify albuminuria.

    Strip categories differ between products and cannot assign an albuminuria category.

  2. Calculate: UACR = 4.2 mg/dL ÷ 60 mg/dL × 1,000 = 70 mg/g.

    Dividing by creatinine corrects for urine concentration.

  3. Classify it: 70 mg/g falls in the A2 range of 30 to 300 mg/g.

    KDIGO categories use the quantitative ratio.

  4. Look for a transient cause in the urinalysis: nitrite and leukocyte esterase are negative.

    Infection and other short-term causes raise albumin temporarily.

  5. Consider the single result: it needs a first-morning specimen for confirmation.

    One high random value can be transient, and persistence defines kidney disease.

Report the UACR as 70 mg/g, in the A2 range. A first-morning specimen confirms it before it is interpreted as persistent albuminuria.

Practice this skill

Your turn

Problem 1 of 3 · Hints available

Sulfosalicylic acid (SSA) is strongly reactive and the routine protein pad is weak. Which explanation fits?

Incorrect. Highly alkaline or heavily buffered urine falsely increases the protein-pad reaction.

Correct. The pad responds most strongly to albumin, and SSA also precipitates globulins and light chains. Quantitative protein measurement and electrophoretic testing are used to investigate the discrepancy. Check the SSA tube for turbidity from contrast media or a drug as well.

Incorrect. SSA precipitates albumin, globulins, and light chains, and contrast media can also cause turbidity. Electrophoresis and immunofixation identify a monoclonal protein.

Hint
  1. The two tests detect protein by different chemistry.
  2. Consider which proteins give the pad its strongest color and which additional proteins SSA detects.

Review Nonalbumin protein

Problem 2 of 3 · Hints available

Urine from a 3-week-old infant gives a negative glucose pad and a positive copper-reduction tablet. The infant has had no medications or vitamin supplements. What do the two results show together?

Sucrose is nonreducing, so it leaves the copper-reduction tablet negative.

The enzyme pad is specific for glucose. That specificity is why it misses galactose and the other reducing sugars the tablet found.

Used the glucose pad to screen for all reducing sugars

Glucose oxidase reacts only with glucose, so galactose, fructose, lactose, and other reducing substances leave the pad negative. Reading a negative pad as no reducing sugar can miss a sugar that copper reduction detects.

Glucose oxidase reacts only with glucose. Copper reduction detects any reducing sugar, so a positive tablet with a negative pad indicates another reducing sugar such as galactose. Specific testing identifies it.

Hint
  1. The glucose pad works through one enzyme with one substrate.
  2. Consider which sugars the copper-reduction reaction detects.

Review Glucose

Problem 3 of 3 · On your own

Put these steps of a manual strip test in order.

  1. Remove excess urine the way the product instructions specify.
  2. Mix the room-temperature urine well.
  3. Confirm acceptable control results for this strip container.
  4. Read the glucose pad at its 30-second time.
  5. Read the leukocyte esterase pad at its 120-second time.
  6. Dip every pad and withdraw the strip, starting the timer as it leaves the urine.
Show the answer

Confirm acceptable control results for this strip container., Mix the room-temperature urine well., Dip every pad and withdraw the strip, starting the timer as it leaves the urine., Remove excess urine the way the product instructions specify., Read the glucose pad at its 30-second time., Read the leukocyte esterase pad at its 120-second time.

Controls come first, so no patient is tested on a failing container. The urine is mixed just before the dip, timing starts as the strip leaves the urine, excess urine is removed, and each pad is read at its own time, glucose early and leukocyte esterase last.

Review Strip workflow and quality control

Use it

Read the case evidence, then make each decision. The step is complete without it.

  • Early shift at the urinalysis bench. The strip container was found uncapped this morning.
  • The positive control reads negative on the protein and glucose pads.
  • Four patient urines are waiting. One is from Hal Geller, 66, who has diabetes. His urine is pale, with a refractometer specific gravity of 1.004.
Decision 1 of 3

What do you do before testing the waiting urines?

Controls check the whole test. With the positive control failing, patient results from this container cannot be reported.

Each pad has its own read time, and a late read has no validated meaning. These pads were exposed to moisture overnight, and extra time does not restore them.

Read every pad at one convenient time

Each pad has its own read time. On one common strip, they run from 30 seconds for glucose and bilirubin to 120 seconds for leukocyte esterase, and a color read after its window is not a valid result. Reading all pads at once misreports the early pads and undercalls a slowly developing leukocyte esterase.

Moisture damages the pads of an open container. Acceptable controls on a properly stored container show the strips are working.

Review Strip workflow and quality control

Decision 2 of 3

On a strip from the new container, Hal's protein pad reads negative. Can his report say he has no proteinuria?

At a specific gravity of 1.004, albumin can be below the pad's detection limit. The pad result is reported as negative, and a negative pad does not exclude proteinuria.

Passing controls shows the strips work. It does not extend the pad's detection to albumin below its limit or to nonalbumin proteins.

Excluded proteinuria from a negative routine protein pad

The protein pad responds most strongly to albumin, so globulins and immunoglobulin light chains can be present with a weak or negative pad, and in a very dilute specimen albumin can fall below the pad's detection limit. Reporting no proteinuria from the pad can miss light-chain protein that sulfosalicylic acid (SSA) precipitation or a quantitative protein test would show.

A second strip uses the same chemistry on the same dilute urine and meets the same limit.

Review Routine protein pad

Decision 3 of 3

His physician asks whether Hal has albuminuria. Which test answers that?

SSA precipitates many proteins and gives a turbidity grade. It cannot give an albumin amount relative to creatinine.

The UACR measures albumin and corrects for urine concentration, and its result places him in an albuminuria category.

Albumin strips report product-specific screening categories. KDIGO categories come from the quantitative UACR.

Assigned an albuminuria category from an albumin strip

Albumin-sensitive strips report product-specific screening categories. Assigning an A2 or A3 category from the strip skips the quantitative urine albumin-to-creatinine ratio (UACR) that classifies albuminuria. One high value can also be transient after exercise, fever, infection, or menstruation.

Review Albumin-to-creatinine ratio

The first problem is the failed positive control on an uncapped container, so no strip from it could be used. After the controls passed, Hal's specific gravity of 1.004 showed why a negative protein pad could not answer his physician's question.

For reference

Sources checked