Measurements in Healthcare

Measurements

Importance of Measurements in Healthcare

• **Patient Safety: **

  • Accurate measurements are crucial in healthcare, impacting patient safety directly.

  • Medication dosage errors as small as a few milligrams can lead to serious consequences.

  • Measurements include patient weight and laboratory test results that influence diagnosis and treatment.

  • Precision is essential.

Significance of Laboratory Measurements

• Accurate Diagnosis:

  • Laboratory results provide objective data confirming or ruling out suspected conditions.

  • Example: A blood glucose level of 250 mg/dL indicates diabetes.

• Treatment Monitoring:

  • Regular measurements track patient responses to treatments.

  • Example: Declining white blood cell counts may signal successful chemotherapy.

• Patient Safety:

  • Measurements can detect dangerous changes before symptoms arise.

  • Example: Rising cardiac enzymes may indicate heart damage prior to chest pain.

Physical Quantities Measured in Laboratories

• Length:

  • Measured in meters; examples include cell size, tissue samples, and bacterial growth zones.

• Volume:

  • Blood samples, reagent solutions, and culture media are measured in liters.

• Time:

  • Reaction durations, centrifugation, and growth periods are tracked in seconds.

• Mass:

  • Mass is the measure for reagent preparation and sample weight.

• Temperature:

  • Influential in incubation conditions, sample storage, and reaction kinetics.

• Light Properties:

  • Measured parameters include absorbance, fluorescence, turbidity, pH, and conductivity.

Seven Basic SI Units

• The SI system defines seven fundamental units forming the basis of measurements in science and medicine:

  • Length: Meter (m)

  • Mass: Kilogram (kg)

  • Time: Second (s)

  • Temperature: Kelvin (K)

  • Amount of Substance: Mole (mol)

  • Electric Current: Ampere (A)

  • Luminous Intensity: Candela (cd)

Understanding Metric Prefixes in Medicine

• Micro- (μ):

  • Used for very small measurements like medication doses (e.g., 250 μg of vitamin B12).

• Milli- (m):

  • Common for liquid medications and lab values (e.g., 5 mL of cough syrup, 100 mg of aspirin).

• Base Unit:

  • Standard measurement without prefix (e.g., 1 gram of tissue sample, 2 liters of IV fluid).

• Kilo- (k):

  • Used for larger measurements like body weight (e.g., 70 kg patient weight).

Importance of Understanding Units

• Laboratory results convey crucial information only when units are understood properly.

• Tests use different units based on substance type and measurement method.

• Fluency in both SI and conventional units is essential for accurate clinical measurements.

Concentration Units

• Units used to express the amount of substance dissolved in a fluid:

  • mol/L or mmol/L:

  • Commonly used for electrolytes, glucose, lactate.

  • mg/dL:

  • Used for glucose, cholesterol.

  • μg/dL:

  • Applied for hormones, lead levels.

Cell Counts

• Used to quantify blood cells or expressed proportions:

  • Cells/μL:

  • For white blood cells (WBCs), red blood cells (RBCs).

  • %:

  • For hematocrit, lymphocyte differential.

  • g/dL:

  • For hemoglobin.

Enzyme & Protein Units

• Used to measure enzyme activity or protein concentration:

  • IU/L:

  • Common for liver enzymes (ALT, AST, ALP).

  • g/L:

  • For total protein, albumin.

  • ng/mL:

  • For troponin, PSA.

Converting Between Metric and English

• Key conversions:

  • 1 kilogram = 2.2 pounds

  • 1 meter = 3.28 feet

  • 1 centimeter = 0.394 inches

  • 1 liter = 1.057 quarts

  • 1 gram = 0.035 ounces

• Example: Patient weight conversion from pounds to kilograms (150 lbs = 68 kg) and height conversion from feet/inches to centimeters (5 ft 8 in = 173 cm).

Errors in Measurement

• Systematic Errors:

  • Consistent, predictable deviations often due to calibration issues, reagent deterioration, or methodological flaws.

• Random Errors:

  • Unpredictable variations caused by environmental fluctuations or human variability (e.g., pipetting technique differences).

• Pre-analytical Errors:

  • Occur before testing begins; issues like patient preparation, improper sample handling, etc.

• Post-analytical Errors:

  • Occur after testing; include transcription errors, incorrect interpretation, or reporting delays.

Introduction to Lab Measurement Tools

• Manual Instruments:

  • Pipettes: Glass, adjustable, multi-channel.

  • Balances: Analytical (0.0001g), precision (0.01g).

  • Glassware: Volumetric flasks, graduated cylinders.

  • Thermometers: Digital, infrared, temperature probes.

  • Microscopes: Bright-field, phase-contrast, fluorescence.

• Automated Systems:

  • Analyzers: Chemistry, hematology, immunoassay.

  • Mass Spectrometers: LC-MS/MS, GC-MS.

  • Flow Cytometers: Cell sorting and characterizing.

  • Automated Liquid Handlers: High-throughput pipetting.

  • Automated Microscopy: Digital imaging systems.

Spectrophotometry

• A quantitative lab technique to measure light absorption at specific wavelengths.

• How It Works:

  • A light source emits a beam at a chosen wavelength.

  • The beam passes through a cuvette containing the solution.

  • A detector measures how much light is transmitted vs. absorbed.

  • The absorbance value calculates analyte concentration using Beer’s Law.

Blood Gas Analyzers

1. pH Measurement:

   • Utilizes a hydrogen ion-selective glass electrode for blood acidity assessment.

   • Normal range: 7.35-7.45.

   • Critical for determining acid-base balance.

2. Oxygen Partial Pressure (pO₂):

   • Measures dissolved oxygen via Clark electrode with an oxygen-permeable membrane.

   • Normal arterial range: 80-100 mmHg, essential for evaluating respiratory function.

3. Carbon Dioxide Partial Pressure (pCO₂):

   • Severinghaus electrode measures CO₂ via pH change in bicarbonate solution.

   • Normal arterial range: 35-45 mmHg, a key indicator of ventilation adequacy.

4. Electrolytes & Metabolites:

   • Modern analyzers measure Na⁺, K⁺, Cl⁻, Ca²⁺, glucose, and lactate simultaneously using ion-selective electrodes and enzymatic sensors for comprehensive assessments.

Cell Counters and Pulse Oximetry

Automated Hematology Analyzers

• Employ multiple technologies:

  • Electrical Impedance: Measures cell size as they pass through an aperture disrupting current.

  • Light Scatter: Differentiates cell types by size and granularity.

  • Fluorescence Flow Cytometry: Labels specific cell markers for detailed classification.

• Parameters measured include RBC, WBC, platelets, hemoglobin, hematocrit, and differential WBC counts.

• Advanced systems flag abnormal cells for microscopic review.

Pulse Oximetry

• Non-invasive method measuring oxygen saturation (SpO₂):

  • Utilizes two light-emitting diodes (660 nm red and 940 nm infrared).

  • Photodetector measures light absorption differences.

  • Normal SpO₂: 95-100%. Values below 90% indicate significant hypoxemia requiring intervention.

Electrophoresis and PCR

Electrophoresis

• Separates molecules based on size and charge in an electric field.

• Applications include:

  • Serum protein electrophoresis

  • Hemoglobin electrophoresis

  • Lipoprotein electrophoresis

  • DNA/RNA gel electrophoresis

Polymerase Chain Reaction (PCR)

• Amplifies specific DNA sequences exponentially for detection and quantification.

• Measurement parameters:

  • Qualitative PCR

  • Quantitative PCR

  • Digital PCR

  • Cycle threshold

Measuring Glucose and Hemoglobin A1c

• Glucose Measurement:

  • Reference range (fasting): 70-99 mg/dL (3.9-5.5 mmol/L).

• Hemoglobin A1c Measurement:

  • Reported as a percentage of total hemoglobin and estimated average glucose (eAG).

  • Diagnostic criteria:

  • < 7.0% (normal)

  • 7.0-8.0% (controlled diabetes)

  • > 8.0% (uncontrolled diabetes).

Enzyme Assays in the Clinical Lab

• Liver Function Enzymes:

  • Normal Ranges:

  • ALT (Alanine aminotransferase): 7-56 U/L

  • AST (Aspartate aminotransferase): 5-40 U/L

  • ALP (Alkaline phosphatase): 44-147 U/L

  • GGT (γ-glutamyl transferase): 8-61 U/L

Water Grades

• Impact of Water Quality in Medical Labs:

  • Analytical results can be significantly compromised by trace impurities, leading to incorrect diagnoses and harmful treatment decisions.

  • Contaminants inhibit enzymatic reactions, alter chemical equilibria, and create background signals that mask true results in sensitive diagnostic assays.

  • Diagnostic integrity is crucial; poor water quality is a risk to patient care and safety.

Water Types Overview

• Type I Water:

  • Ultra-high purity for critical applications. Rigorous quality control.

• Type II Water:

  • High quality for most laboratory analyses; less stringent than Type I but maintains excellent purity.

• Type III Water:

  • Moderate purity; used for less sensitive procedures and as feed water for Type I systems.

• Type IV Water:

  • Basic laboratory grade; minimal purification for non-critical applications.

Applications of Different Water Types

• Type I Water:

  • Molecular diagnostics and PCR, sensitive enzyme assays, trace element analysis.

• Type II Water:

  • General laboratory testing, media and reagent preparation, clinical chemistry analyzers, microbiological culture media.

• Type III Water:

  • Glassware rinsing, feed water for Type I/II systems, basic solution preparation, water bath applications.

• Type IV Water:

  • Basic cleaning procedures, initial feed water for higher-grade purification, non-critical laboratory processes.

Water Purification Systems

1. Pretreatment:

   • Removes particulates, chlorine, and hardness minerals.

2. Primary Purification:

   • Reverse osmosis can remove up to 99% of contaminants.

3. Secondary Purification:

   • Deionization or distillation further removes ions.

4. Polishing Technologies:

   • Address specific contaminants (e.g., UV oxidation, ultrafiltration).

Distillation Process and Properties

• Distillation:

  • Involves boiling water and condensing the steam into a clean container, effectively removing most common minerals.

Reverse Osmosis Water Purification

• The semi-permeable membrane technique removes contaminants larger than water molecules, including bacteria, colloids, and particulates.

Challenges in Water Storage and Distribution

• Quality degrades over time due to:

  • CO₂ absorption from air.

  • Contaminant leaching from storage materials.

  • Bacterial growth and biofilm formation.

  • Accumulation of environmental particles.

• Usage Recommendations: Type I/Grade 1 water should be used immediately or stored under controlled conditions for minimal time.

Impact of Poor Water Quality

• Analytical Interference:

  • Increased background readings in assays, false results, shifting calibration curves.

• Equipment Damage:

  • Mineral scale buildup, corrosion, clogging of instrument pathways.

Chemical Grades

Definition

• Chemical Grades:

  • Refers to the purity levels of reagents in testing; determines suitability for specific uses.

Determining Factors

• Purity Standards:

  • Governing bodies like ISO maintain specifications for chemical grades.

• Certification Documentation:

  • Manufacturers provide quality certificates detailing purity and testing methods.

Most Common Chemical Grades

• Technical Grade:

  • Lowest purity; for industrial use.

• Laboratory Grade:

  • Suitable for general lab work.

• CSC Grade:

  • High purity standards for clinical applications.

• Analytical Grade:

  • Essential for precision in clinical chemistry.

• Pharmaceutical Grade:

  • For research and testing.

• Specialty Grades:

  • For molecular biology.

Effects of Grade on Laboratory Results

• Low-Grade Reagents:

  • Can introduce variability and noise leading to false results.

• High-Grade Reagents:

  • Enhance consistency, reproducibility, and accurate quantitation.

Regulatory Standards for Medical Labs

CLIA Requirements

• Documentation for reagent quality and evidence of compliance with manufacturer’s claims.

• Records of reagent handling and verification of quality.

ISO 15189 Standards

• Procedures must be documented, reagents tracked, and performance verified to ensure accuracy and reproducibility in test results.

Reagents in Clinical Labs

Definition

• A reagent:

  • A substance added to a system to cause or test for a chemical reaction.

Roles of Reagents

• Identification:

  • React with specific substances to identify diseases or conditions.

• Quantification:

  • Determine precise concentrations of substances in samples.

• Quality Control:

  • Verify that instruments and processes function correctly for reliable results.

Organic vs Inorganic Reagents

• Organic Reagents:

  • Carbon-based, used in organic chemistry and biochemical assays.

• Inorganic Reagents:

  • Mineral-based compounds for basic reactions and tests.

Reagent Storage and Handling

• Temperature Control:

  • Store at recommended temperatures and prevent light exposure.

• Contamination Prevention:

  • Use airtight containers and never return unused reagents.

• Labeling System:

  • Clearly mark date, concentration, and preparer's initials.

Types of Laboratory Reagents

• Acids & Bases:

  • pH adjustment and digestion agents.

• Salts:

  • Used in buffers, culture media.

• Solvents:

  • Dissolve samples for analysis.

• Buffers:

  • Maintain stable pH in reactions.

• Biological Stains:

  • Visualize cells in microscopy.

• Commercial Kits:

  • Pre-packaged and quality-controlled for consistency.

Common Reagents

70% Alcohol

• Properties:

  • Mixture of ethanol and purified water; optimal for microbial killing.

• Laboratory Applications:

  • Disinfecting surfaces, skin antisepsis, preserving specimens.

Acid Alcohol

• Composition:

  • 3% hydrochloric acid in ethanol; used as a decolorizer in staining procedures.

Solvents in Medical Labs

• Water:

  • Universal solvent; various grades used based on requirements.

• Ethanol:

  • Used for disinfection and extraction; common for fixing specimens.

• Acetone:

  • Strong solvent for cleaning glassware; highly flammable.

Lot-to-Lot Reagent Variation

• Sources of Variation:

  • Variability can arise from differences in raw materials or storage.

• Validation Procedures:

  • New lots should be tested alongside existing ones to ensure result accuracy.

Essential Solution Terminology

• Solution:

  • Homogeneous mixture created by combining solute and solvent.

• Solute:

  • Substance dissolved in a solution, usually in smaller quantities.

• Solvent:

  • Dissolving agent, typically water in the lab.

• Dilution:

  • The process of making a solution less concentrated by adding solvent.

Controls and Standards

Reconstitution

• Quality controls are provided as lyophilized reagents needing reconstitution with the correct reagent water for accurate use.

Buffers

Definition

• A buffer resists pH changes when acids or bases are added, critical for maintaining test integrity.

  • Composed of weak acid or base with its conjugate, stabilizing pH.

Importance in Laboratory

• Enzyme Functionality:

  • Most enzymes need stable pH for activity; deviations can denature proteins and coat assay reliability.

• Result Accuracy:

  • Consistent pH leads to reliable test results crucial for clinical decisions.

• Method Standardization:

  • Buffers ensure procedures can be compared reliably across laboratories.

Chemistry of Buffer Systems

• Acidic Buffers:

  • Pair of weak acid and conjugate base.

  • Example: Acetic Acid (CH₃COOH) + Sodium Acetate (CH₃COONa).

• Basic Buffers:

  • Pair of weak base and conjugate acid.

  • Example: Ammonia (NH₃) + Ammonium Chloride (NH₄Cl).

Buffer Capacity

• Buffer Capacity:

  • The amount of acid/base a buffer can neutralize before pH changes significantly.

• Preparing a Buffer Solution:

  • Steps include selecting components, calculating concentrations, weighing/dissolving, checking pH, and final volume adjustments.

pH Measurement

Definition

• pH:

  • Measurement of hydrogen ion concentration, ranging from 0 to 14:

  • 0-6.9: Acidic

  • 7.0: Neutral

  • 7.1-14: Alkaline/Basic

pH Measurement Techniques

• Litmus Paper:

  • Provides qualitative pH estimates through color changes.

• pH Meters:

  • Delivers accurate, quantitative readouts.

• Electrodes:

  • Measure electrical potentials correlated with hydrogen ion concentration.

Accumet AB pH Meters

• The Accumet AB series, especially the AB315 model, is favored in labs for its accuracy and functionality.

Temperature Compensation in pH Measurement

• pH measurements are temperature-dependent affecting electrode sensitivity and ionic movement.

• Accurate calibration is needed for reliable results in clinical applications.

Performing pH Measurement

1. Calibration:

   • Use appropriate buffer solutions for calibration.

2. Preparation:

   • Rinse electrode with deionized water, do not wipe.

3. Measurement:

   • Immerse electrode in sample and ensure it is covered.

   • Document values meticulously following protocols.

Upcoming Quiz

• Next Week: Quiz in Clinical Laboratory Science, Chapter 4 planned.