Instruments and Analytical Techniques

General Considerations

Sample Handling

• Patient ID: Ensure proper identification of the patient for accurate result attribution.

• Sample Collection:

  • Use appropriate anticoagulants/preservatives as necessary.

  • Handle sample transport and storage with care to maintain integrity.

• Evaluation/Accessioning: Verify sample quality upon receipt in the laboratory.

• Processing and Storage: Follow protocols for processing samples appropriately and managing their storage.

Sample Analysis

• Key Characteristics:

  • Accurate: Measurements should reflect the true value.

  • Precise: Consistency across measurements.

  • Sensitive: Detects low concentrations of analytes.

  • Specific: Distinguishes between different analytes efficiently.

  • Ideal Characteristics:

  • Cost-effective, easy to perform, and quick turnaround.

Instrumentation and Measurement

• Instrumentation/Method: How equipment affects results.

• Accuracy of Measurement: Factors to consider include calibration and linearity, as well as sources of error.

• Quality Assurance and Quality Control: Procedures to ensure reliable results.

• Reference Intervals (Reference Ranges): Set by population studies; essential for interpreting patient results.

• Patient Variables: Factors affecting test results include collection timing, age, pregnancy status, posture, exercise, and nutritional status.

Interpretation of Results

• Reference Interval Checks:

  • Verify results against established reference ranges.

  • Compare with previous results to identify significant changes (delta check).

• Biological vs. Analytical Variation: Understanding the differences between variations originating from biological factors and those arising from analytical processes.

• Clinical Consistency: Results should align with the patient's clinical presentations.

• Critical Values: Identification of values that indicate severe clinical conditions (panic values).

• Reporting Requirements: Results presented in SI units, e.g., mole/L, with additional conversion guidelines provided in Appendix D.

Advantages of Automation in Clinical Chemistry

• Increased precision, sensitivity, and specificity of methods.

• Improved throughput: More samples can be processed per hour.

• “Walk-away” capabilities reduce manual labor and associated costs.

• Minimizes variability in results between laboratories and between different technicians.

• Reduces manual errors in processes such as pipetting and calculations.

• Limited sample and reagent requirements lead to lesser waste.

Steps in Automation

1. Specimen Preparation: Initial handling and processing of samples for analysis.

2. Specimen Identification: Ensuring that each sample is correctly identified throughout the analysis process.

3. Specimen Measurement and Delivery: Automated processes to measure and transport samples.

4. Reagent Systems/Reagent Delivery: Automated dispensing of necessary reagents.

5. Chemical Reaction Phase: Involves mixing, separation of interferences, incubation, and managing reaction time.

6. Measurement: Finalizing the analytical process through measurement.

7. Signal Processing and Data Handling: Converting raw results into interpretable data.

8. Calibration, Reporting, and Monitoring: Ongoing adjustment and documentation of results to ensure accuracy.

Chemistry Specimens

• Common specimen types include:

  • Serum

  • Plasma

  • Urine

  • Body Fluids: e.g., cerebrospinal fluid (CSF), pleural fluid, peritoneal fluid, amniotic fluid.

  • Feces

Definitions related to Clinical Chemistry

General Terms

• Core Lab: Central laboratory handling a wide range of tests.

• Automation: Use of machines to perform tests with minimal human intervention.

• Batch Analysis: Performing the same test across multiple samples simultaneously.

• Continuous Flow: Processes where multiple tests occur simultaneously.

• Centrifugal Analysis: Techniques that involve centrifugal forces to separate materials.

• Discrete Analysis: Each test is conducted in separate, isolated cuvettes.

• Random Access: Ability to load samples on demand, including urgent (STAT) tests.

• Barcode: Automated data entry method utilized to track specimens.

• Carry-over: Transfer of sample residue from one specimen to another, potentially leading to contamination.

Specific Terms

• Throughput: Maximum number of samples processed per hour.

• Dead Volume: The volume of fluid that remains in a system after processing.

• Dwell Time: Time from sample collection to obtaining analytical results.

• Incubation: Time allowed for reactions to occur under controlled conditions.

• Test Repertoire: Types of tests a laboratory offers.

• Open System: Instruments that can use reagents from different vendors.

• Closed System: Instruments that utilize manufactured reagents exclusively.

Quality Assurance in Automation

• Factors affecting quality assurance in automated settings:

  • Risk of human error during sample loading.

  • Ensuring sample integrity and proper prioritization.

  • Verification processes to confirm pipetting accuracy.

  • Management of carryover through means like wash stations and air scrubbing.

  • Maintaining optical clarity and cleanliness of reusable reaction vessels.

  • Implementing effective inventory control measures.

Analytical Techniques

Basic Disciplines

• Spectrometry:

  • Includes methods like spectrophotometry and mass spectrometry.

• Luminescence:

  • Various forms, including fluorescence and chemiluminescence.

• Electroanalytical Methods:

  • Comprising techniques like electrophoresis, potentiometry, and amperometry.

• Chromatography:

  • Types include gas chromatography, liquid chromatography, and thin-layer chromatography.

• Emerging Methods:

  • Developments in point-of-care (POC) testing.

CSMLS Competencies for Analytical Techniques in Chemistry

• Laboratory analyses must apply principles across:

  • Microscopy - including staining, light measuring systems like absorption, emission, and reflectometry.

  • Electrochemical systems, electrophoresis, chromatography, osmometry, and immunoassays as stated in competencies 4.01 to 4.07.

Examples of Analytical Techniques

Previously Learned Techniques

• Manual Measurement Techniques:

  • e.g., Spectrophotometry for total protein, albumin, creatinine, urine total protein (UTP).

• Semi-automated Measurement:

  • Reflectance photometry, osmometry, and pH measurements.

• Automated Measurement:

  • Methods include spectrophotometry and electrochemical measurement, as exemplified by the Beckman DXC.

Analyzers in the Lab

• Potentiometry / Ion Selective Electrode:

  • Types include Beckman DXC (indirect) and Radiometer ABL 90 Flex (direct).

• Absorption Spectrophotometry:

  • Analyzer type: DXC.

• Reflectometry and Turbidimetry:

  • Analyzers include Siemens Clinitek and DXC respectively.

• Osmometry:

  • Analyzer: Advanced Instruments Osmometer.

• Chemiluminescence:

  • Analyzer: Centaur.

Absorption Spectrometry

Fundamental Principles

• Definition: An analyte generates color upon a chemical reaction, visible light is absorbed as it passes through a solution containing that analyte.

• Key Terms:

  • Absorbance: The amount of light absorbed by a sample.

  • Transmittance: The ratio of the light that passes through the solution compared to the incident light.

Absorbance Relationship

• The relationship between light transmitted and solute concentration is both inversely proportional and logarithmic.

• Formula:
  $A = 2 - ext{log}_{10}( ext{T})$
  where (A) is absorbance and (T) is percent transmittance.

Beer-Lambert Law

• Equation: $A = ext{ε}bc$

  • Where:

  • (A) = Absorbance

  • (ε) = Molar absorptivity

  • (b) = Path length of light through the solution (typically 1 cm)

  • (c) = Concentration of the solution.

• Molar absorptivity can change based on the wavelength (λ).

Calibration and Usage

• Calibration Curves: Determine unknown concentrations using a sample curve derived from known standards.

  • Calibration curve plotting: Concentration on the x-axis vs absorbance on the y-axis.

  • Maintain uniform increments to ensure linearity and accurate readings.

One Point Calibration

• When conditions are stable:

  • $C<em>u = A</em>u C<em>s / A</em>s$

  • Where:

  • (C_u) = Concentration of unknown

  • (A_u) = Absorbance of unknown

  • (A_s) = Absorbance of standard

  • (C_s) = Concentration of standard.

Spectral Absorbance and Calibration

Characteristics of Calibration Curves

• Calibration curves require plotting standard concentrations and their corresponding absorbances but should not include patient absorbances or control absorbances.

• A best-fit line through the origin without extending past the last standard should be applied. Proper labeling of concentration values, units, analyte name, wavelength, instrument, and method used is essential.

Use of Calibration Curves

• Perform control and unknown tests in the same manner as standards.

• Determine unknown concentration by visualizing its absorbance against the calibration curve.

• An example includes determining the concentration for an absorbance of 0.400.

Sample Handling and Cuvette Usage

Cuvette Types

• Square cuvettes: Most accurate due to lower refraction and consistent orientation.

• Round cuvettes: Simple but can cause inconsistencies due to inconsistent diameters.

• Disposable options available, with materials varying based on wavelength applications (glass, plastic, or quartz).

Proper Use of Cuvettes

• Ensure complete cleanliness of cuvettes to minimize errors.

• Orientation of cuvettes in the holder should be consistent.

• Rinse flow cells to eliminate carryover from previous samples.

Photodetectors and Signal Processing

Photodetector Types

• Function: Convert electromagnetic radiation into an electrical signal proportional to photon counts.

• Types of Detectors Include:

  • Photocell

  • Phototube

  • Photodiode array

  • Photomultiplier tubes (PMT) which enhance sensitivity significantly.

• PMT functionality: Light strikes a cathode, emitting electrons which are amplified through dynodes before producing a readable current.

Signal Processing

• The process involves amplifying electrical signals, removing unwanted noise, and converting signals from analog to digital forms.

• Algorithms and calculations may include converting percent transmittance to absorbance values.

• Blanking Procedures: Set blank controls for reference analysis to ensure accuracy in readings.

  • Types of blanks include reagent blanks and sample blanks.

Quality Assurance in Spectrophotometry

• Importance of regular checks on accuracy, stray light, and linearity to maintain instrument integrity.

• Implement standard solutions to verify wavelengths and identify any interferences affecting transmittance and absorbance.

Emission Spectrophotometry

Applications

• Examples include fluorometry, luminometry, chemiluminescence, and bioluminescence.

Fluorometry Details

• Processes involve compounds absorbing light at specific wavelengths and re-emitting it at higher wavelengths.

• Loss of energy due to collision or heat is significant, impacting fluorescent measurements.

Chemiluminescence vs Fluorescence

• Chemiluminescence does not necessitate excitation radiation and generally features a simple setup more advantageous in terms of speed and simplicity.

• Fluorescence has precise detection systems handling voltage transitions and requires careful manipulation of excitation sources.

• Advantageous applications include immunoassays, DNA probe assays, and point-of-care diagnostics.

Turbidimetry and Nephelometry

Basic Functions

• Turbidimetry: Measure light blockage in a sample with suspended particles.

• Nephelometry: Measures scattered light instead of transmitted light, improving sensitivity.

Measurement Principles

• Turbidimetry measures light intensity decrease due to concentration of particles.

• Nephelometry detectors focus on light scatter at various angles to capture specific particle interactions.

Reflectance Photometry

• Measures light reflected off colored reactions using chromophores in solid areas.

• Ratio of reflected light determines concentration, needing mathematical adjustments for accurate responses.

Point-of-Care Testing (POCT)

Overview

• POCT encompasses miniaturized, portable analytical methods for healthcare environments, emphasizing speed, accessibility, and less invasive procedures.

• Limitations may include cost, accuracy compared to laboratory settings, and operational issues with non-laboratory personnel.

POC Test Types

• Common examples include glucometers, electrolyte and blood gas assessments, pregnancy tests, and fecal occult blood tests.