Clinical Chemistry Case Study

Clinical Chemistry Case Study (7103406, 2CHs)

• Course covers biochemical and molecular basis of human diseases using case study approach.
• Clinical findings and diagnostic investigations are presented along with thorough discussion of underlying pathophysiological mechanisms.
• Diagnostic and therapeutic approaches used by clinical chemistry laboratory investigations will be discussed.

Introduction to the Course

• Introduces course content.
• Discusses the concept of health and disease, including the WHO definition of health (1948).
• Details the concept of disease by covering etiology, pathogenesis, morphology/histology, clinical manifestations, diagnosis, and disease course.

Etiology

• Etiologic factors are the causes of diseases.
• Categorized as biologic agents (bacteria, viruses), physical forces (trauma, burns, radiation), chemical agents (poisons, alcohol), and genetic inheritance.
• Most disease-causing agents are nonspecific and can affect multiple organs.
• Some diseases result from a single agent or traumatic event affecting multiple organs.
• Examples include cystic fibrosis, sickle cell anemia, and familial hypercholesterolemia.
• Most disease states are multifactorial (cancer, heart disease, diabetes).
• Risk factors are multiple factors predisposing to a disease.
• Types of diseases: congenital (present at birth), acquired (after birth) genetic (caused by genetic mutations), and hereditary (passed down genetically)
• Latrogenic: caused by medical intervention
• Idiopathic: an unknown cause

Pathogenesis

• Explains the sequence of cellular and tissue events in response to an etiologic agent until the disease's expression.
• Understanding the pathogenesis explains how a disease evolves.
• Etiology and pathogenesis differ, though often used interchangeably.
• Atherosclerosis is often cited as the etiology of coronary artery disease; in reality, the inflammatory process describes the pathogenesis.

Morphology

• Morphology refers to the fundamental structure and form of cells and tissues.
• The study of morphology includes gross (visible) and microscopic structure changes characterizing a disease.
• A lesion is pathologic or traumatic discontinuity of body organ(s) or tissue(s).
• Examining lesions often involves radiographs, ultrasonography, and biopsy for histological study.

Clinical Manifestations

• Diseases manifest in various ways; some produce symptoms like fever, while others are silent at onset.
• Signs are observable characteristics (elevated temperature, swollen extremities).
• Symptoms are subjective complaints (pain, difficulty breathing).
• Manifestations relate to the primary disorder or represent compensatory mechanisms by the body.
• Syndromes are groups of signs and symptoms characteristic of a particular disease.
• Complications are adverse extensions of a disease or treatment outcomes.

Clinical Course

• Examines how diseases evolve.
• Diseases can have acute, subacute, or chronic courses.
• Acute disorders are relatively severe and self-limiting.
• Chronic implies continuous long-term processes.
• Subacute diseases are intermediate in severity and duration.
• Clinical disease is characterized by signs and symptoms.
• Subclinical disease is not apparent clinically but is identified via tests (antibodies, cultures).
• Preclinical stage: disease not yet clinically apparent but progressing to clinical disease (examples: prediabetes, prehypertension, Hepatitis B).
• Patient can be a carrier if harboring organism but no clinical manifestations. Carrier status can be limited or chronic.

Diagnosis

• Diagnosis is identifying the nature of a disease.
• The diagnostic process involves:
• Careful history taking (symptoms, progression, contributing factors).
• Careful physical examination.
• Ordering diagnostic tests (validate suspected problems, rule out other problems, check progress/symptoms).

Clinical Biochemistry Laboratory and Test Parameters

• Discusses the role of the laboratory in medicine and diagnosing diseases.
• Laboratory tests are medical procedures that analyze blood, urine or body fluid samples.
• Common tests include screening tests (congenital hypothyroidism), diagnostic tests, preventative tests and monitoring tests (drug therapy effects).
• Core tests involve biochemistry (frequently requested).
• Specialized tests are less common and are used for rare diseases or referral centers.
• Lists common tests.

Specimen Collection

• Blood specimens.
• Whole blood (analyzed quickly)
• Serum
• Plasma (anticoagulants such as EDTA or lithium heparin)
• Urine: preservative added, size appropriate for 24-hour collection.
• Other specimens are required for other tests. Specific protocols are required.

Test Request Priorities

• Stat (immediately): Life-threatening emergencies.
• Urgent (ASAP): Results within 3 hours.
• Timed: Collected at specific time.
• Routine: Collected at regular times, 8–24 hours; no priority required.

Laboratory Testing Cycle

• The entire process of ordering a test, performing the tests, collecting results, interpreting the results, and reporting.
• Consists of pre-analytical, analytical, and post-analytical phases.

Blood Sampling Errors

• Errors that can happen during obtaining patient specimens.
• Prolonged stasis, improper collection technique, inappropriate sampling site, insufficient specimen, incorrect specimen containers, storage or transport issues.

Urine Specimens

• Specimens, preservatives, and collection considerations.

Performance of a Test

• Validation involves comparing test results to a "gold standard."
• Test characteristics include sensitivity (correctly identifies affected individuals) and specificity (correctly identifies non-affected individuals), and positive/negative predictive values in assessing prevalence effect on the accuracy of results.
• Understanding factors like disease prevalence and population composition is important for interpreting test results; predictive values vary with these factors
• Test outcomes can be positive or negative
• Sensitivity, specificity, positive predictive value, negative predictive value
• Community sample sizes

Data Interpretation & Predictive Values

• Data is used to interpret test performance.
• Positive predictive value (PPV): Proportion of patients with positive test results who actually have the disease.
• Negative predictive value (NPV): Proportion of patients with negative test results who actually do not have the disease.
• Prevalence of a disease has a significant impact on predictive values (example: HIV in low and high risk populations).