Reagent Strips for Urine Testing

Reagent Strips

• Reagent strips provide a rapid method for routine urine chemical testing.
• Single and multiple-test strips are available, with the choice determined by laboratory preference.
• Strips consist of chemical-impregnated absorbent pads on a plastic strip.
• A color-producing reaction occurs when the pad contacts urine.
• Results are interpreted by comparing the color to a manufacturer-provided chart.
• Several shades of color indicate semi-quantitative readings (negative, trace, 1+, 2+, 3+, or 4+).
• Some charts also give estimations in mg/dL.
• Automated readers use SI units.
• Proper technique involves dipping the strip briefly into the specimen, removing excess urine, blotting the edge, and waiting the specified time before reading.
• Properly mixed urine is crucial to avoid errors; elements like blood cells might settle to the bottom.
• A reliable light source is essential for accurate color interpretation.
• Visual inspection of the strip for discoloration or deterioration before testing is necessary.
• Avoid using strips past their expiration date.

Quality Control of Reagent Strips

• Run positive and negative controls at least once per 24 hours, or more frequently.
• Run additional controls when questions arise or when a new strip bottle is opened.

Reporting of Bacteria and Amorphous Crystals

• Reporting categories for bacteria and crystals are light, moderate, and heavy.

Urine pH

• Urine pH is regulated by the lungs and kidneys.
• A healthy specimen's pH is usually slightly acidic (5.0-6.0) in the morning, and may be more alkaline after a meal.
• The normal range is 4.5 to 8.0.
• Factors influencing pH include blood acid-base balance, renal function, UTI, diet, and specimen age.
• Standing urine tends to be alkaline.
• A pH exceeding 8.5 suggests an aged or incorrectly stored specimen.

Confirmatory Testing

• Confirmatory tests use different methods to detect substances with similar or higher sensitivity/specificity than reagent strips.
• Chemical tests using tablets and liquids are options for problematic results.
• These additional tests must be validated using their own positive and negative controls.

Urine Protein

• Normal urine contains minimal protein (<10 mg/dL).
• Proteinuria may suggest various conditions, including prerenal, renal, and postrenal causes.
• Excessive protein in urine may indicate damage to the glomeruli (glomerular proteinuria), tubules (tubular proteinuria), or issues beyond the kidneys (postrenal proteinuria).
• Prerenal proteinuria is due to increased filtration from conditions like exercise and fever.
• Renal proteinuria results from damage to the glomerular membrane or tubules.
• Postrenal proteinuria is due to conditions after the kidneys.
• Microalbuminuria is a critical indicator, especially in diabetes mellitus, where it indicates reduced glomerular filtration and eventual renal failure.

Creatinine

• Reagent strips for creatinine measure its concentration in the urine.
• The principle is based on a peroxidase reaction involving creatinine, forming colorimetric changes, using copper sulfate as an active component which converts the creatinine to a detectable color.
• Elevated results may indicate factors like hematuria or specific medication use.

Glucose

• Glucose is a frequent urine test, used in physical exams, mass screenings, and diabetes detection.
• The renal threshold for glucose is 160 to 180 mg/dL; exceeding it causes glycosuria in urine.
• Glycosuria can also be seen in non-diabetic conditions.

Ketones

• Ketones, produced by fat metabolism, appear in urine during insufficient carbohydrate metabolism, such as in diabetes, starvation, or dehydration.
• Clinical importance includes detecting diabetes mellitus, metabolic abnormalities, and monitoring treatment efficacy.
• Ketone levels are often reported as negative, trace, small, moderate, or large.

Blood

• Hematuria denotes the presence of intact red blood cells, indicating various urinary tract issues—kidney stones, glomerular disease, tumors, and trauma, amongst other causes.
• Hemoglobinuria arises from damaged red blood cells and appears as clear, reddish urine.
• Hemosiderinuria is seen as yellow-brown sediment due to iron deposits.
• Myoglobinuria is red-brown urine due to muscle tissue breakdown.

Bilirubin

• Bilirubin, a byproduct of red blood cell breakdown, is usually not present in urine.
• Elevated levels may suggest liver damage, like hepatitis or cirrhosis, or blockages in the biliary tract.

Urobilinogen

• Urobilinogen is a product of bilirubin metabolism.
• High levels often indicate liver or biliary tract issues.
• Low levels might occur in bile duct obstruction.

Nitrite

• Nitrite in urine arises from the reduction of nitrates by bacteria.
• Positive nitrite commonly indicates a urinary tract infection.
• Reporting categories are negative or positive.

Leukocyte Esterase

• Leukocyte esterase is a diagnostic marker for urinary tract infections (UTIs).
• A positive result indicates the presence of white blood cells in the urine.
• Reporting categories are negative, trace, small, moderate, or large.

Specific Gravity

• Specific gravity reflects the concentration of solutes in the urine, not a direct measure of hydration.
• Normal fluctuations occur throughout the day.
• Specific gravity is related to the pKa of a polyelectrolyte in an alkaline environment.

This quiz explores the use of reagent strips for routine urine chemical testing. Participants will learn about the types of strips available, the importance of proper technique, and how to interpret results accurately. Key aspects like color changes and the need for reliable lighting also feature prominently.