Urine Reagent Strip (Chemical Examination) - Vocabulary Flashcards

Vocabulary flashcards covering key terms, concepts, tests, principles, interpretations, and interferences in the chemical examination of urine using reagent strips. Cards focus on definitions to aid memory for exam preparation.

Reagent strip (dipstick)

A narrow plastic strip with attached pads containing reagents for multiple urine tests; used for simultaneous chemical screening; read against a brand color chart.

Pad (on reagent strip)

Individual test pad on the strip that contains reagents for a specific urine analyte.

Color chart

Brand-specific guide used to compare pad colors and determine negative/positive results; results must be read within the specified time.

Hold horizontally

Position the strip so the pads remain horizontal during testing to prevent erroneous results.

Dipping time

Dip the strip into urine briefly; do not exceed 1 minute for immersion.

Canister storage

Store reagent strips at room temperature; viable below 30°C; check expiration date to prevent discrepancies.

Expiration date

Date after which the reagent strips may give unreliable results; always check before use.

Reading time frame

Read and interpret each pad within its specified time window as different tests have different time frames.

Quality control (QC)

Use positive and negative controls at least once every 24 hours and when opening a new bottle to assure accuracy.

Glycosuria (urine glucose)

Presence of glucose in urine; indicates possible hyperglycemia/diabetes; detected via enzyme reactions on a strip.

Glucose oxidase

An enzyme used in reagent strips to oxidize glucose, initiating a color-changing reaction.

Peroxidase (in glucose test)

An enzyme that reacts with the oxidized glucose product to yield a color change via a chromogen.

Chromogen

A color-producing compound in the test pad; examples include potassium iodide and tetramethylbenzidine.

Buffer

Part of the test pad chemistry that maintains pH during the reaction in glucose testing.

Reading colors (glucose test)

Results are reported as negative, trace, 1+, 2+, 3+, or 4+ based on color intensity.

Glycosuria clinical significance threshold

Generally occurs when blood glucose exceeds ~160–180 mg/dL, indicating renal threshold is exceeded.

Causes of glycosuria

Hyperglycemia (diabetes), pancreatitis, acromegaly, Cushing syndrome, pheochromocytoma, gestational diabetes, and related conditions.

Interferences in glucose test (false positives)

Hydrogen peroxide and detergents can cause false positives; other reducing sugars do not typically cause false positives.

Interferences in glucose test (false negatives)

Ascorbic acid, high ketones, high specific gravity, low temperatures, and prolonged standing can cause false negatives.

Benedict’s test

Copper-reduction test for reducing substances in urine; older method to detect glucose (not used with strips today).

Clinitest tablet

A copper-based tablet (copper sulfate, sodium carbonate, sodium citrate, NaOH) used with water/urine to produce a color change upon heating.

Urine proteins

Presence of increased protein in urine; an indicator of renal disease; normal urine has low protein content.

Albumin

Most sensitive urine protein; normally present in trace amounts; elevated levels indicate potential renal pathology.

Tamm-Horsfall protein (uromodulin)

A normal urine protein contributed by the kidney; part of the baseline protein detected in dipstick testing.

Protein error of indicators

A principle where proteins change the pH indicator’s color, allowing detection of protein (often with acid buffer around pH 3.0).

Protein indicators (pads)

Indicators such as tetrabromophenol blue, tetrachlorophenol, or tetrabromosulfonphthalein used in the protein pad.

Protein color change (pad)

In the presence of protein, indicator shifts from yellow (acidic) to green/blue (alkaline).

Three categories of proteinuria

Pre-renal, Renal (glomerular), and Tubular; plus Orthostatic (postural) and Microalbuminuria as subtypes.

Pre-renal proteinuria

Proteinuria due to plasma abnormalities before reaching the kidneys (e.g., hemolysis, inflammation, multiple myeloma).

Renal (glomerular) proteinuria

Proteinuria from glomerular damage (e.g., lupus, glomerulonephritis) causing impaired filtration.

Tubular proteinuria

Proteinuria from tubular dysfunction (e.g., Fanconi syndrome, heavy metal poisoning) with failed reabsorption of low-molecular-weight proteins.

Orthostatic (postural) proteinuria

Benign proteinuria occurring after several hours of standing and resolving with recumbency.

Microalbuminuria

Small increases in albumin in urine; early sign of diabetic nephropathy and cardiovascular risk.

Urine ketones

Ketone bodies as an alternative fuel source when carbohydrate utilization is impaired; includes acetoacetate, acetone, and beta-hydroxybutyric acid.

Ketone testing reagents

Sodium nitroprusside reagent on strips; reacts with acetoacetate to yield a purple color; Acetest tablet contains glycine to detect acetone.

Ketone testing (false positives/negatives)

False positives: phthalein dyes, pigmented urine, levodopa; false negatives: prolonged standing urine.

Acetest tablet test

Tablet test using sodium nitroprusside and glycine to detect urine ketones; color graded as negative, small, moderate, large.

Urine bilirubin

Conjugated bilirubin (B2) detected by a diazo-based reaction; indicates liver or biliary disease when present.

Unconjugated bilirubin (B1)

Bilirubin bound to albumin and not excreted in urine; not present unless liver dysfunction allows leakage.

Diazo reaction (bilirubin)

Reaction of conjugated bilirubin with a diazonium salt on the test pad to produce a pink/purple azodye.

Bilirubin detection interferents

False positives: indicans, highly pigmented urine, phenazopyridine; false negatives: exposure to sunlight, ascorbic acid.

Ictotest tablet

Tablet test to confirm bilirubin; uses SSA, boric acid, diazonium salt to produce blue-purple color in urine.

Urobilinogen

Product of bilirubin metabolism; normally present in small amounts; tested by Chemstrip (diazo) or Multistix (Ehrlich’s reagent).

Urobilinogen clinical significance

Increased with liver disease, hemolytic anemia; normally <1 mg/dL; recirculation between intestine and liver.

Urobilinogen testing methods

Chemstrip uses diazo reaction; Multistix uses Ehrlich’s aldehyde reaction to produce color.

Interferences in urobilinogen test

False positives: porphobilinogen, indicans, some drugs; false negatives: prolonged standing urine, formalin, high nitrite.

Urine occult blood

Dipstick test capable of detecting small amounts of RBCs or free Hb/myoglobin; color change indicates presence.

Hematuria vs hemoglobinuria vs myoglobinuria

Hematuria: intact RBCs in urine; Hemoglobinuria: free Hb from lysed RBCs; Myoglobinuria: myoglobin from muscle breakdown.

Occult blood testing principle

Pseudoperoxidase activity from heme catalyzes oxidation of a chromogen (e.g., tetramethylbenzidine) producing color change.

Interferences in occult blood test

False positives/negatives from drugs, high oxidants, recent meals, or improper timing.

Leukocyte esterase (LE)

An enzyme from neutrophils detected in urine indicating pyuria/UTI; reported as negative to 4+.

Leukocyte esterase clinical significance

Positive LE suggests urinary tract infection or inflammation; not definitive without culture.

Leukocyte esterase interferences

False positives: strong oxidants, formalin, highly pigmented urine; false negatives: high protein or certain antibiotics.

Nitrite test in urine

Detects nitrate-reducing bacteria; requires bladder time (about 4 hours) for nitrite to form; positive LE+nitrite suggests UTI.

Nitrite testing principle

Greiss reaction; nitrite forms with a diazonium salt to yield a pink color.

Nitrate/nitrite clinical significance

Positive nitrite indicates bacterial infection; helps diagnose cystitis; may prompt culture.

Urine pH (indicator system)

Double indicator system using methyl red and bromothymol blue to determine pH range (pH 4-9).

Urine specific gravity (SG)

Indicator system using polyelectrolyte ions; changes color with SG; read with pH indicators; reject at pH 9.0.

pH and SG relationship in dipsticks

Higher SG shifts indicator color; pH affects readings; separate readings for pH and SG are provided.

Reject pH 9.0

Discard specimen if urine pH reads 9.0 or higher due to unreliability.

Reagent strip chart (LE)

Guides the color change of leukocyte esterase on the strip and is used with other Urine RBC tests.

Vitamin C interference on strips

Vitamin C can cause interferences affecting up to 11th pad (and across several parameters) leading to false results.