Urinalysis 2

MLTD 1207 Clinical Chemistry I: Urinalysis Lecture Notes

Introduction

  • Lecture on urinalysis as part of the Clinical Chemistry I course at Nova Scotia Community College.

  • Emphasizes the importance of the content for students in clinical laboratory sciences.

  • Copyright information stating that unauthorized reproduction, storage, transmittal, or distribution is prohibited.

Reagent Strips

  • Major Brands:

    • 1. Multistix (Bayer)

    • 2. Chemstrip (Roche)

How Reagent Strips Work

  • Reagent strips consist of chemical-impregnated absorbent pads attached to a plastic strip.

  • A color-producing chemical reaction occurs upon contact with urine.

  • Reaction times vary by test, ranging from immediate reaction (e.g., pH) to up to 120 seconds (e.g., leukocyte esterase).

  • Refrigerated specimens need to warm to room temperature (RT) before testing due to the temperature dependence of enzymatic reactions.

Care of Reagent Strips

  • Storage Guidelines:

    1. Store in a cool, dry place.

    2. Protect from moisture and excessive heat.

    3. Keep the cap tightly on the container except when retrieving strips.

    4. Avoid touching impregnated areas with fingers to prevent contamination.

Multistix 10 SG - Visual Observation

  • Steps for testing:

    1. Immerse all reagent areas in urine specimen briefly and remove immediately.

    2. Run the edge of the strip along the rim of the container to remove excess urine.

    3. Compare the colors to the color chart according to the indicated times.

Chemical Examination of Urine Components

  • Components assessed include:

    • pH

    • Specific Gravity

    • Protein

    • Glucose

    • Ketones

    • Blood

    • Nitrite

    • Leukocyte Esterase

    • Bilirubin

    • Urobilinogen

pH Control Systems

  • Three systems regulate body pH:

    1. Kidneys

    2. Lungs

    3. Acid-base buffers

  • Bodily production of net acid (e.g., carbonic acid, lactic acid, keto acids) daily, which must be excreted by the kidneys.

Kidneys' Role in Acid-Base Balance

  • Key functions include:

    • Reabsorption of bicarbonate.

    • Excretion of ammonium ions.

    • Excretion of free hydrogen ions and weak organic acids.

Acid-Base Status Evaluation

  • Utilizes the bicarbonate-carbonic acid buffer system to assess the acid-base status using pH and pCO2 measurements.

  • The calculated HCO3 parameter helps differentiate between metabolic and respiratory conditions.

Measurement of Urine pH

  • Depends on tubular secretion of hydrogen ions and ammonia production by distal convoluted tubule cells.

  • Normal pH Range:

    • Random samples: 4.5 - 8.0

    • First morning specimen: slightly acidic (5.0–6.0)

    • Post-meal: more alkaline (alkaline tide)

    • Lowest pH possible: 4.4; highest pH: 8.5

  • High-protein diets lead to more acidic urine, while vegetarian diets yield more alkaline urine.

  • pH variations measured in 0.5 increments using two indicators (methyl red and bromthymol blue).

Clinical Significance of pH

  • Helps determine the origin of acid-base disorders (respiratory vs. metabolic).

  • Indicates kidney’s function regarding acid/base secretion and reabsorption.

  • Urinary crystals may precipitate based on urinary pH, affecting calculi risk (e.g., calcium oxalate forms in acidic urine).

  • Maintenance of acidic pH aids in UTI treatment (through diet and medications).

  • Bacterial growth at room temperature can raise urine pH, indicative of poor sample preservation.

Specific Gravity Assessment

  • Definition: The density of urine compared to distilled water at similar temperature.

  • Influenced by the number and size of particles (e.g., urea, Na, Cl).

  • Reflects kidneys’ ability to reabsorb essential chemicals and water.

Testing and Reading Specific Gravity

  • Methods include:

    • Urinometer

    • Refractometer

    • Reagent strip

    • Automation systems

  • Refractometry Principle: Measures concentration of dissolved particles by assessing the refractive index.

Specific Gravity Results Interpretation

  • Interpretation Standards:

    • Specific gravity < 1.002 may not be urine.

    • High specific gravity indicates kidney function issues; dilution factor may be considered.

    • Subtraction of high-molecular-weight substances (e.g., protein, glucose) for accurate kidney concentration ability measurement.

Protein as a Key Indicator

  • Importance of Protein Testing:

    • Best indicator of renal disease.

    • Types of proteinuria identified include:

    • Prerenal: Not due to kidney disease; e.g., hemoglobin, myoglobin, overload conditions (overflow proteinuria).

    • Renal: Due to damage or disease to glomeruli or tubules, such as glomerular nephritis.

    • Postrenal: Result of infections, trauma, or contamination.

Protein Testing Methodologies

  • Error Sources: Protein error of indicators, false positives, and negatives relative to substance concentration and urine pH.

  • Microalbumin Testing: Essential for early diabetic nephropathy detection and cardiovascular risk assessment.

Glucose in Urine

  • Significance: Indicates possible diabetes or other metabolic disorders.

  • Glucose typically filtered and reabsorbed in the proximal convoluted tubule until renal threshold (approximately 8.9-10.0 mmol/L).

  • Testing methods include glucose oxidase method and Clinitest (copper reduction method).

Guidelines and Interferences in Testing

  • Clinitest: Targets reducing sugars but not glucose-specific.

  • Hematological and physiological interferences influence results; precautions must be taken to ensure accuracy.

Ketone Testing

  • Definition: Measures acetone, acetoacetic acid, and beta-hydroxybutyric acid levels reflecting fat metabolism.

  • Ketones emerge primarily in diabetes, starvation, heavy exercise, or malabsorption conditions.

  • Reagent strips utilize the sodium nitroprusside method to detect ketones and may produce false positives due to certain dyes.

Interpretation of Blood in Urine

  • Types:

    • Hematuria: Presence of intact RBCs.

    • Hemoglobinuria: Free hemoglobin resulting from RBC lysis.

    • Myoglobinuria: Presence of myoglobin post muscle injury or necrosis.

Nitrite Testing for Infections

  • Utilized in detecting urinary tract infections by identifying nitrite presence from nitrate-reducing bacteria.

  • Methodology includes the Greiss reaction and assessing sensitivity against bacterial cultures.

Leukocyte Esterase (LE) Testing

  • Detects presence and quantity of leukocytes in urine as an indicator of urinary tract infection.

  • Positive LE results typically correlate with other infection markers like nitrite testing.

Bilirubin and Urobilinogen Testing

  • Bilirubin indicates liver disease or bile duct obstruction, while urobilinogen can signify liver function deficits.

  • Testing methodologies include diazo reactions and specific assays for urobilinogen.

Automation in Urinalysis

  • Clinitek System: Employs reflectance photometry for urinalysis, aiming for improved reproducibility and standardized reporting.

  • Discusses advantages and weaknesses of both manual and automated testing.

Conclusion and References

  • Notes conclude with alerting students to the importance of accuracy and methodology consistency in urinalysis.

  • References cited include "Urinalysis and Body Fluids, 6th Edition" by Strasinger and DiLorenzo, confirming the importance of this knowledge for clinical laboratory practice.