Clinical chemistry

Clinical chemistry, also referred to as chemical pathology, clinical biochemistry, or medical biochemistry, is a specialised division within pathology and medical laboratory sciences concerned with the qualitative and quantitative analysis of biologically significant compounds in bodily fluids and tissues. These compounds, known as analytes or biochemical markers, are measured using a variety of analytical techniques and dedicated laboratory instruments. The field integrates principles from medicine, biology, chemistry, biomedical engineering, informatics, and applied biochemistry. Emerging in the late nineteenth century with the introduction of basic chemical reactions to test components of blood and urine, it has evolved into a technologically advanced discipline essential to modern diagnostic medicine.

Historical Development and Scope

Clinical chemistry originated with simple manual laboratory tests such as colour changes in the presence of specific chemical reagents. These early methods provided rudimentary assessments of glucose, proteins, and nitrogenous waste products. Progress during the twentieth century led to more sophisticated qualitative and quantitative assays, which revolutionised diagnostic capabilities. By the mid-twentieth century, automated analysers became a defining feature in clinical laboratories. These instruments enabled high-throughput processing of specimens, rapid turnaround times, and enhanced accuracy.
Today, clinical chemistry laboratories employ a broad range of technologies, including spectrometry, chromatography, photometry, optics, and potentiometry, to detect subtle changes in the biochemical properties of naturally occurring analytes. Such advances permit the identification of enzymes, ions, electrolytes, metabolites, and molecular markers that reflect organ function and overall health status. Clinical chemists serve as essential intermediaries between laboratory data and clinical decision-making, advising clinicians on appropriate test selection, interpretation of abnormal findings, and the implications of laboratory results for diagnosis, prognosis, monitoring, and therapeutic guidance.

Common Analytes and Diagnostic Applications

Clinical chemistry routinely evaluates a diverse array of analytes that provide diagnostic insights into multiple organ systems. Common categories include:

• Electrolytes: Sodium, potassium, chloride, and bicarbonate, all vital for fluid balance, neuromuscular function, and acid–base homeostasis.
• Renal function markers: Urea and creatinine, which indicate kidney filtration efficiency and are used to monitor acute and chronic kidney disorders.
• Liver function tests: Including the albumin–globulin ratio, bilirubin (total, direct, indirect), alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl transferase (GGT), and alkaline phosphatase (ALP).
• Cardiac markers: Such as B-type natriuretic peptide (BNP), used in the evaluation of heart failure.
• Endocrine markers: For example adrenocorticotropic hormone (ACTH).
• Metabolic and miscellaneous indicators: HbA1c for long-term blood glucose control; blood gas measurements including partial pressures of carbon dioxide and oxygen; and markers relevant to toxicology, such as drugs and chemical toxins.
• Oncology-related markers: For instance neuron-specific enolase (NSE).
• Stool-based screening tests: Faecal occult blood testing (FOBT) for gastrointestinal pathology.

Blood and urine remain the most commonly analysed specimens, with serum and plasma forming the principal sample types. The selection of a specific biological matrix is guided by the biochemical nature of the analyte being tested.

Test Panels and Their Clinical Importance

Physicians frequently request panel tests, which involve groups of related assays performed on a single specimen. These panels provide broader clinical information than individual tests and enhance diagnostic accuracy and efficiency. Panel tests tend to deliver high predictive value and are considered cost-effective for screening, monitoring, and disease confirmation.

Metabolic Panels

A metabolic panel (MP) is widely used for routine health evaluation, hospital monitoring, and the investigation of suspected systemic disorders. It assesses kidney and liver function, electrolyte balance, and acid–base status.
There are two principal forms:

• Basic Metabolic Panel (BMP): A standard panel consisting of eight analytes measured in plasma. It typically includes sodium, potassium, chloride, bicarbonate, blood glucose, urea, creatinine, and calcium. These measurements collectively illuminate kidney function, metabolic status, hydration, neuromuscular activity, and acid–base equilibrium.
  • Electrolytes: Sodium, potassium, chloride, and carbon dioxide regulate the distribution of fluids, acid–base balance, and neuromuscular activity.
  • Calcium: Essential for bone integrity, muscle contraction, nerve function, and coagulation. Abnormal calcium levels may indicate bone disease, endocrine disorders, or metabolic dysfunction.
  • Glucose: A critical energy source. Persistently elevated levels may reflect diabetes mellitus or insulin resistance.
  • Urea and Creatinine: Waste products filtered by the kidneys. They offer insight into renal function, metabolic disorders, and dialysis effectiveness, and are valuable in monitoring patients on diuretic therapy.
• Comprehensive Metabolic Panel (CMP): An expanded panel of 14 tests, which includes all BMP components plus total protein, albumin, alkaline phosphatase, ALT, AST, and bilirubin. These additions provide a deeper evaluation of hepatic function, nutritional status, and systemic metabolic integrity.

Specimen Processing

Before analysis, blood specimens often require processing to isolate plasma or serum. Centrifugation is the principal method used, separating cellular components from the liquid fraction. Plasma is obtained when anticoagulated blood is centrifuged prior to clotting, while serum is produced after clot formation. Modern automated analysers frequently incorporate pre-analytical functions such as specimen identification, aliquoting, and centrifugation, thereby minimising handling errors and enhancing laboratory workflow.

Laboratory Instruments and Automation

Contemporary clinical laboratories depend heavily on highly automated analysers capable of processing hundreds of different tests and handling large daily workloads. While large institutions may offer extensive test catalogues, certain specialised or low-demand assays are often referred to external reference laboratories. Continuous quality control ensures accuracy, reproducibility, and compliance with regulatory standards. Automation also extends to data management systems, sample routing, and integration with electronic medical records.

Subspecialities in Clinical Chemistry

The field encompasses several subspecialised domains, each addressing particular diagnostic needs:

• General or Routine Chemistry: Analysis of common analytes, often focused on assessing renal and hepatic function.
• Special Chemistry: Advanced or manual techniques, including protein electrophoresis, specialised enzymatic assays, and unique biochemical markers.
• Endocrinology: Hormone analysis and the diagnosis of endocrine disorders.
• Toxicology: Detection and quantification of drugs of abuse, poisons, and chemical agents.
• Therapeutic Drug Monitoring (TDM): Ensuring optimal dosing of medications with narrow therapeutic ranges.
• Urinalysis and Body Fluid Chemistry: Chemical evaluation of urine, cerebrospinal fluid, and serous effusions for metabolic and infectious diseases.
• Faecal Analysis: Assessment for gastrointestinal disorders, including occult bleeding.