Exam

• What Clinical Chemistry Is
    - Clinical chemistry analyzes body fluids using chemical processes to diagnose, monitor, and treat disease.
    - Defined as: “Clinical chemistry uses chemical processes to analyze BFs and measure levels of specific analytes to help docs diagnose, monitor, treat disease.”

• Common Specimens
    - Serum: liquid after clotting
    - Plasma: liquid with anticoagulant
    - Other specimens: urine, cerebrospinal fluid (CSF), synovial fluid, pleural fluids

• Role of the Medical Laboratory Technician (MLT)
    - Quality Control (QC)
    - Calibration
    - Interpretation of critical values
    - Troubleshooting: Responsibilities include QC, calibration, result interpretation, and troubleshooting issues.

2. URINALYSIS BASICS

• Three Components
    1. Physical: Color, clarity, odour, volume
    2. Chemical: Analyzed using a dipstick
    3. Microscopic: Examination of cells, casts, crystals

• Why We Do Urinalysis
    - To diagnose and monitor diseases
    - To monitor treatment effectiveness
    - To screen for congenital and hereditary diseases: “Diagnoses and monitors disease; Screens population for asymptomatic conditions.”

3. PRE-ANALYTICAL REQUIREMENTS

• Collection Rules
    - Label specimen with name, ID, and date/time of collection.
    - Treat all specimens as potentially infectious.
    - Use a clean, dry container for collection.
    - First morning urine is preferred for testing: “Specimen is labelled; First specimen voided in morning is preferred.”

• Examine Within 2 Hours
    - Urine must be examined within 2 hours of collection to avoid changes:
      - Bacteria convert urea to ammonia, increasing pH, leading to the destruction of cells/casts: “Urea-splitting bacteria produce ammonia… increase in pH… casts/certain cells decompose.”

4. TYPES OF URINE SPECIMENS

• Random Urine Specimens
    - Most common type of urine specimen.
    - Can be dilute, leading to falsely low analyte results.

• First Morning Urine
    - Best specimen for routine urinalysis (UA) and microscopy.
    - Most concentrated specimen with the highest analyte/cell levels.

• Midstream Clean Catch
    - Best for cultures and sensitivities (C&S).
    - Reduces risk of contamination: “Specimen of choice for culture and sensitivity… reduced incidence of contamination.”

• 24-Hour Urine
    - Collected for analytes with diurnal variation (e.g., creatinine, urea, sodium, potassium, catecholamines).
    - Must be refrigerated during collection.

• Catheter, Suprapubic, and Pediatric (U-bag)
    - Used when patients cannot void normally.

5. PHYSICAL PROPERTIES

• Colour
    - Normal range: yellow to amber.
    - Key pigments:
      - Urochrome (yellow)
      - Uroerythrin (red)
      - Urobilin (orange-yellow)

• Clarity
    - Ranges from clear to turbid; cloudiness may indicate the presence of crystals, cells, mucus, yeast, or powders.

• Odour
    - Ammonia smell can occur if urine is left standing due to bacterial breakdown of urea.

• Specific Gravity (SG)
    - Normal range: $1.002–1.035$
    - Used to measure kidney concentrating ability and hydration status.
    - High SG: indicates dehydration or diabetes.
    - Low SG: suggests dilute urine.

• Osmolality
    - Considered more reliable than SG as it is not affected by glucose/protein levels.
    - Normal range: $500–800 ext{ mOsm/kg}$
    - In end-stage renal failure, osmolality approximates that of plasma: approximately $285 ext{ mOsm/kg}$.

6. CHEMICAL TESTS (DIPSTICK)

• pH
    - Normal range: $4.6–8.0$
    - Indicators used: Methyl red and bromothymol blue.
    - No major interferences reported.
    - Old urine can give false increased alkalinity.

• Protein
    - Clinical Meaning
      - Key indicator of renal disease.
      - Causes of proteinuria include:
        - Glomerular damage
        - Tubular damage
        - Pre-renal (Benign Jaffe Protein, hemoglobin)
        - Lower tract infection
    - Principle of testing: Protein error of indicators—albumin binds the indicator at constant pH, causing a colour change.
    - False Positives:
      - Alkaline urine
      - Quaternary ammonium compounds (quats) or cleaners
      - Blood substitutes
    - False Negatives:
      - Benign Jaffe Protein (BJP)
      - Globulins
      - Hemoglobin if no albumin present

• Blood (RBCs, Hgb, Myoglobin)
    - Clinical Meaning
      - Indicates bleeding from any point from the glomerulus to the urethra
      - Associated with kidney stones, tumors, infections.
    - Principle: Heme’s pseudo peroxidase activity oxidizes chromogen resulting in color change.
    - False Positives:
      - Bleach
      - Bacterial peroxidases
    - False Negatives:
      - Ascorbic acid
      - High specific gravity (SG)

• Nitrite
    - Meaning: Screens for urinary tract infections (UTIs) caused by gram-negative bacilli only.
    - Requires urine to sit in the bladder for at least 4 hours for accurate results.
    - False Negatives:
      - Non-nitrite-producing organisms (e.g., enterococci, yeast)
      - Insufficient bladder incubation time

• Leukocyte Esterase
    - Meaning: Detects white blood cells (WBCs) indicating UTI or inflammation.
    - False Positives:
      - Bleach
      - Formalin
    - False Negatives:
      - High glucose
      - High SG
      - Certain antibiotics

• Glucose
    - Meaning: Indicates diabetes or renal threshold issues.
    - Principle: Glucose oxidase reaction produces hydrogen peroxide (H₂O₂), leading to peroxidase reaction and color change.
    - False Negatives:
      - Vitamin C (ascorbic acid)
      - High SG
      - Old urine (if bacteria consume glucose)
    - False Positives:
      - Bleach
      - Other oxidizers

• Ketones
    - Meaning: Indicate fat metabolism (DKA, starvation, keto diet).
    - Principle: Nitroprusside reaction causes a purple color change.
    - False Positives:
      - Sulfhydryl drugs
      - High SG

• Bilirubin & Urobilinogen
    - Meaning: Associated with liver disease, biliary obstruction, and hemolysis.
    - Principles of testing:
      - Bilirubin: diazo reaction
      - Urobilinogen: Ehrlich reaction or diazo reaction (depends on test strip).
    - False Negatives:
      - Light exposure (bilirubin is converted to biliverdin)
      - Ascorbic acid
      - Nitrite affecting bilirubin results

7. COMMON DIPSTICK INTERFERENCES

• Highly Pigmented Urine
    - Can mask color changes, resulting in false positives (“Pigment stains the reagent pad… impossible to distinguish.”)

• Bleach
    - Triggers oxidation-based tests leading to false positive results.

• Run-off Between Pads
    - Protein pad acid buffer potentially lowers pH of surrounding pads affecting results.

• Vitamin C
    - Causes false negatives for glucose, blood, bilirubin, and nitrite results: “Ascorbic acid… reacts with peroxide before chromogen.”

8. MICROSCOPIC EXAM

• Triggered by detection of protein, RBCs, WBCs, or nitrites.
    - Casts identified during examination provide significant clinical relevant findings:
      - Hyaline casts: normal or due to dehydration
      - RBC casts: indicate glomerulonephritis
      - WBC casts: indicate pyelonephritis
      - Granular casts: associated with renal disease
      - Waxy casts: indicate chronic renal failure
      - Fatty casts: suggest nephrotic syndrome (“Waxy cast… severe CRF… Fatty cast… nephrotic syndrome.”)

9. QUALITY CONTROL (QC)

• Two Levels Required:
    - Normal and abnormal samples must be tested: “Two levels… one normal… one abnormal.”

• If QC Fails:
    - Required actions:
      - Re-run the analysis
      - Use a new vial
      - Check the analyzer
      - Do NOT release patient results: “If ALL fails, call the company (do not release PT results).”

• Westgard Rules:
    - Quality control guideline interpretations include:
      - 1₂s = warning
      - 1₃s = reject
      - 2₂s = systematic error
      - R₄s = random error
      - 4₁s = systematic error
      - 10x = shift

10. POCT (Point-of-Care Testing)

• Advantages:
    - Fast turnaround time (TAT)
    - Requires small sample volumes
    - Enables immediate clinical decisions

• Disadvantages:
    - Higher costs
    - QC/QA challenges
    - Operator variability: “Cost… reagents expire… hard to control inventory.”

• QC in POCT includes:
    - Internal controls (C-line)
    - External controls (liquid controls)
    - Daily quality control
    - New lot quality control

11. SPECTROPHOTOMETRY

• Beer-Lambert Law:
    - Relationship defined as: A=$\epsilon$lc

• - States that absorbance is proportional to concentration and path length: “Absorbance… proportional to its [ ] and path length.”

• Components of a Spectrophotometer:
    - Light source
    - Monochromator
    - Cuvette
    - Detector
    - Readout display

• Reflectance vs. Absorbance:
    - Absorbance: Light passes through sample.
    - Reflectance: Light reflects off the surface (used in dry slides and urinalysis strips).

12. TURBIDIMETRY & NEPHELOMETRY

• Turbidimetry:
    - Measures decrease in transmitted light.
    - Commonly used for quantifying proteins and bacterial growth.

• Nephelometry:
    - Measures scattered light.
    - Used for immunoglobulins and C-reactive protein (CRP): “Scattered light… proportional to insoluble complexes.”

13. CHROMATOGRAPHY & MASS SPECTROMETRY

• Chromatography:
    - Technique that separates analytes by their affinity for the mobile vs. stationary phase.
    - Types include:
      - Gas Chromatography (GC): Suitable for volatile compounds (e.g., toxic screens, alcohols).
      - Liquid Chromatography (LC): Ideally used for large/fragile molecules (e.g., vitamin D, hormones).

• Mass Spectrometry:
    - Measures the mass-to-charge ratio:
      - GC-MS: Analyzes small stable molecules.
      - LC-MS: Analyzes large fragile molecules: “Used to ID and weigh chemicals… measures mass:charge ratio.”

14. AUTOMATION

• Benefits:
    - Quicker turnaround times (TAT)
    - Less error margin
    - Requires smaller sample volumes
    - Improved safety: “Reduction in medical errors… reduced specimen volume… improves safety.”

• Analyzer Types:
    - Continuous flow analyzers
    - Centrifugal analyzers
    - Discrete analyzers (industry standard)
    - Vitros Analyzer: Uses dry slide technology combined with reflectance spectrophotometry: “Dry slide… spreading layer filters proteins/lipids.”

15. LEAN SIX SIGMA & QC

• Lean: Aim to eliminate waste, outlined by the acronym DOWNTIME:
    - Defects
    - Overproduction
    - Waiting
    - Non-utilized talent
    - Transport
    - Inventory
    - Motion
    - Extra processing

• Six Sigma: Focus on reducing variation, defined mathematically as:
  sigma=TEa-Bias/CV

        (TEa=total allowable error, bias= systematic error, CV=coefficient of variable)

  - A higher sigma indicates a more reliable test: “A 6-sigma assay is extremely stable… 3-sigma is unstable.”

16. METHOD EVALUATION

• Assessment criteria include:
    - Linearity
    - Precision
    - Accuracy
    - Recovery
    - Interference
    - Patient comparison: “Recovery… interference… patient sample comparison.”

17. REFERENCE INTERVALS & DIAGNOSTIC EFFICIENCY

• Reference Interval: Defined as the middle 95% of the healthy population.

• Diagnostic Terms:
    - Sensitivity: Proportion calculated as: Sensitivity= TP/TP+FN
    - Specificity: Proportion calculated as: Specificity= TN/TN+FP
    - Positive Predictive Value (PPV) and Negative Predictive Value (NPV): Important in diagnostic evaluations.

18. EXTERNAL QUALITY ASSESSMENT (eQA)

• Quality assessment includes:
    - Use of blind samples from organizations such as IQMH, CAP, OWA.
    - Standard Deviation Index (SDI) calculation defined as: SDI=lab mean - group mean/SD
    - Interpretation: SDI greater than 3 is deemed unacceptable: “SDI… > ±3.0 unacceptable.”