Study Notes on Chemical Pathology and Laboratory Testing

INTRODUCTION TO CHEMICAL PATHOLOGY

INTRODUCTION

• Instructor: Dr. S. Ametepe

OUTLINE OF THE SESSION

• Introduction to chemical pathology
• Specimen collection & handling
• Side room testing/point of care testing/near patient testing

OBJECTIVES

• Describe the biochemical and pathophysiological mechanisms of diseases and the biochemical principles underlying their treatment.
• Select appropriate laboratory tests and interpret the results to confirm or refute a provisional clinical diagnosis and to monitor progress during treatment.
• Understand the potentials and limitations of various laboratory tests.
• Collect the right type of specimens for laboratory investigations under the right conditions.

CHEMICAL PATHOLOGY

DEFINITIONS

• Chemical Pathology: The systematic study of biochemical processes associated with health and disease, and the measurement of constituents in body fluids or tissues to facilitate diagnosis of diseases.
• Clinical Biochemistry: Often used interchangeably with Chemical Pathology, focuses on the biochemical aspects of disease.
• Medical Biochemistry: Another related term that emphasizes the study of the chemistry of biological systems in health and disease.
• Pure Blood Chemistry and Physiological Chemistry are subfields under this spectrum.

ROLE OF CHEMICAL PATHOLOGY IN HEALTHCARE

• Diagnosis: Assists in differentiating between various diseases based on clinical history and examination.
• Monitoring: Evaluates disease progression or treatment response (e.g., monitoring diabetic patients).
• Screening: Detects diseases in healthy populations before they become symptomatic.
• Prognosis: Offers insights into disease susceptibility, such as cholesterol levels predicting coronary artery disease risks.
• Provides tools for clinicians in diagnosing and managing a variety of disorders.

IMPORTANCE OF CHEMICAL PATHOLOGY

• Provides consultation on appropriate testing for specific clinical scenarios.
• Interprets a broad spectrum of clinical laboratory tests.
• Advises on the limitations of laboratory tests in various conditions.
• Ensures quality laboratory testing through internal and external quality assurance.
• Trains medical students on proper testing selection and cost-effective laboratory use.
• Focuses on selecting the right test, at the right time, for the right patient while considering factors that might affect the test outcomes.

ANALYSES PERFORMED IN CHEMICAL PATHOLOGY LABORATORIES

Types of Bodily Fluids Analyzed:

• Whole blood, serum or plasma, urine, cerebrospinal fluid, faecal material, effusions, seminal fluid, sweat, and amniotic fluid.

Common Tests and Their Purposes:

• Whole Blood, Serum, or Plasma Tests:
  • Albumin: Investigates water balance disorders, liver diseases, and protein-energy malnutrition.
  • Urea & Creatinine: Assesses renal function.
  • Glucose: Diagnoses and monitors diabetes.
  • Bilirubin: Monitors jaundice, especially in newborns.
  • Amylase: Diagnoses acute pancreatitis.
  • Liver Enzymes (ALT): Evaluates liver disease status.
  • Electrolytes (Potassium & Sodium): Monitors electrolyte disturbances.
• Cardiac Markers: Detects cardiac damage.
• Endocrinology Tests: Assesses various hormone levels including pituitary, sex hormones, thyroid, and adrenal hormones.
• Inherited Metabolic Diseases: Evaluates metabolic disorders.
• Therapeutic Drug Monitoring: Ensures medication levels are within therapeutic ranges.
• Drug Abuse Testing: Identifies substance abuse.
• Specialized Testing: Environmental, occupational health, and insurance testing including tumor markers like PSA.

QUALITY ASSURANCE (QA) IN CHEMICAL PATHOLOGY

Definition and Importance:

• Quality Assurance is defined by WHO as a comprehensive process whereby the quality of laboratory reports and outcomes can be guaranteed.
• Ensures reliability, reproducibility, and relevance of laboratory test results.

Components of Quality Assurance Programs:

• Internal Quality Control (IQC): Daily checks to maintain accuracy and precision of test results.
• External Quality Assessment (EQA): Compares laboratory results with other institutions to ensure standardization and accuracy.

PRE-ANALYTICAL STAGE OF CHEMICAL PATHOLOGY TESTS

Factors Influencing Pre-analytical Quality:

• Proper preparation of patient, collection, and transport of specimens.
• Collection techniques (e.g., venipuncture, avoiding hemolysis).
• Specimen labeling and preservation conditions (e.g., protecting samples from light).

Common Issues Leading to Sample Rejection:

• Unlabeled specimens, incorrect specimens, leaking containers, contamination, delays in transport.

ANALYTICAL STAGE OF CHEMICAL PATHOLOGY TESTS

• Covers test principles, reagents, controls, equipment, and quality control procedures.

Types of Errors in Analysis:

• Random Errors: Inconsistent results due to uncontrollable variables.
• Systematic Errors: Predictable inaccuracies due to insufficient controls or faulty equipment.

POST-ANALYTICAL STAGE OF CHEMICAL PATHOLOGY TESTS

• Includes result reporting, verification, and interpretation.
• Maintain organization of test report information and ensure timely delivery to healthcare providers.

Trouble with Interpretation of Results:

• Continuous evaluation of test results alongside clinical findings.
• Reference ranges must be adhered to for meaningful interpretation of test outcomes.

Clinical Sensitivity and Specificity Definitions:

• Clinical Sensitivity: The percentage of true positives in a disease presence scenario.
• Clinical Specificity: The percentage of true negatives in a disease absence scenario.

Importance of Predictive Values:

• Positive Predictive Value (PPV): Assesses proportion of true positives among positive results.
• Negative Predictive Value (NPV): Assesses proportion of true negatives among negative results.

POINT-OF-CARE TESTING (POCT)

• Also referred to as near-patient testing or bedside testing. Used to perform tests outside the traditional laboratory setting—critical for acute patient needs.

Settings for Effective Use:

• Emergency departments, clinics, and patient self-testing environments.

Examples of POCT Tests:

• Glucose determination, hemoglobin testing, coagulation assessments.

Advantages and Disadvantages:

• Advantages include shorter turnaround times and immediate treatment; disadvantages focus on potential analytical performance issues and cost implications.

CONCLUSION

• Understanding Chemical Pathology is crucial for accurate diagnosis, monitoring, and effective patient management in healthcare settings.
  • Focus on Quality Assurance across all stages of laboratory processes to enhance reliability and patient outcomes.

INTRODUCTION

• Instructor: Dr. S. Ametepe

OUTLINE OF THE SESSION

• Introduction to chemical pathology
• Specimen collection & handling
• Side room testing/point of care testing/near patient testing

OBJECTIVES

• Describe the biochemical and pathophysiological mechanisms of diseases and the biochemical principles underlying their treatment.
• Select appropriate laboratory tests and interpret the results to confirm or refute a provisional clinical diagnosis and to monitor progress during treatment.
• Understand the potentials and limitations of various laboratory tests.
• Collect the right type of specimens for laboratory investigations under the right conditions.

CHEMICAL PATHOLOGY

DEFINITIONS

• Chemical Pathology: The systematic study of biochemical processes associated with health and disease, and the measurement of constituents in body fluids or tissues to facilitate diagnosis of diseases.
• Clinical Biochemistry: Often used interchangeably with Chemical Pathology, focuses on the biochemical aspects of disease.
• Medical Biochemistry: Emphasizes the study of chemistry in biological systems as it relates to health and disease.
• Pure Blood Chemistry and Physiological Chemistry are related subfields.

ROLE OF CHEMICAL PATHOLOGY IN HEALTHCARE

• Diagnosis: Assisting clinicians in differentiating between differential diagnoses (e.g., identifying causes of acute abdominal pain).
• Monitoring: Evaluating the effectiveness of therapy or disease progression.
  • Example: HbA1c for long-term glycemic control in diabetes.
• Screening: Detecting subclinical disease in seemingly healthy individuals.
  • Example: Newborn screening for phenylketonuria (PKU).
• Prognosis: Assessing the severity and future risk of a disease.
  • Example: Use of B-type Natriuretic Peptide (BNP) in heart failure.

IMPORTANCE OF CHEMICAL PATHOLOGY

• Provides clinical consultation on testing patterns.
• Detailed interpretation of complex test panels.
• Quality Assurance to ensure results are medically fit for purpose.
• Training healthcare professionals on cost-effective laboratory utilization.

ANALYSES PERFORMED IN CHEMICAL PATHOLOGY LABORATORIES

Types of Bodily Fluids Analyzed:

• Blood (Whole blood, serum, or plasma), Urine, Cerebrospinal Fluid (CSF), Effusions (Pleural, Peritoneal), Seminal fluid, Sweat, and Amniotic fluid.

Common Tests and Their Purposes:

• Renal Function Tests (RFTs):
  • Urea & Creatinine: Key markers for Glomerular Filtration Rate (GFR).
• Liver Function Tests (LFTs):
  • Albumin: Assesses synthetic function and nutritional status.
  • ALT/AST: Indicators of hepatocellular injury.
  • ALP/GGT: Markers for cholestasis.
• Carbohydrate Metabolism:
  • Glucose: Diagnosis of Diabetes Mellitus and investigation of hypoglycemia.
• Lipid Profile:
  • Cholesterol and Triglycerides to assess cardiovascular risk.
• Cardiac Markers:
  • Troponins (I or T) and CK-MB: Used to detect myocardial infarction (heart attack).
• Endocrinology:
  • Thyroid Stimulating Hormone (TSH), Free T4, and Cortisol.

QUALITY ASSURANCE (QA)

• Internal Quality Control (IQC): Monitors precision (reproducibility) on a daily basis using control materials with known values.
• External Quality Assessment (EQA): Monitors accuracy by comparing laboratory results against a peer group of other laboratories.

PRE-ANALYTICAL STAGE

• Patient Preparation: Fasting requirements (e.g., $12$ hours for lipids) and timing (e.g., diurnal variation for cortisol).
• Biological Factors: Age, sex, posture, and recent exercise.
• Specimen Handling: Immediate separation of serum from cells to prevent leakage of potassium (pseudohyperkalemia).
• Sample Rejection Criteria: Hemolysis, icterus (high bilirubin), or lipemia (fat-rich samples).

ANALYTICAL STAGE

• Focuses on the chemical reaction and measurement.
• Random Errors: Errors that vary without a predictable pattern (e.g., bubbles in reagents).
• Systematic Errors: Persistent errors due to calibration shifts or reagent deterioration.

POST-ANALYTICAL STAGE

• Critical Results: Immediate notification to clinicians for life-threatening values.
• Reference Ranges: Comparison of patient results to a standardized range derived from a healthy population.

CLINICAL PERFORMANCE METRICS

• Clinical Sensitivity: Ability of a test to correctly identify those with the disease.
  • $\text{Sensitivity} = \frac{\text{True Positives (TP)}}{\text{True Positives (TP)} + \text{False Negatives (FN)}} \times 100$
• Clinical Specificity: Ability of a test to correctly identify those without the disease.
  • $\text{Specificity} = \frac{\text{True Negatives (TN)}}{\text{True Negatives (TN)} + \text{False Positives (FP)}} \times 100$
• Predictive Values (PPV & NPV): Determine the probability that a positive or negative result truly represents the patient's state.

POINT-OF-CARE TESTING (POCT)

• Advantages: Improved clinical outcomes through "turnaround time" reduction.
• Disadvantages: Higher cost per test, potential for poor documentation, and variability in operator skill.
• Governance: Must be overseen by the central laboratory to ensure quality standards.