Overview
Clinical Biochemistry deals with the study of biochemical events or parameters in the body. It covers the enzymes routinely measured in serum, the liver and renal function panels used to assess organ health, and the pre-analytical steps of specimen collection that determine whether a laboratory result can be trusted.
This lesson also introduces general laboratory practice β equipment calibration, Standard Operating Procedures (SOPs) and safety measures β that every medical laboratory technologist must follow to produce accurate, reproducible and safe results.
Learning Objectives
After this lesson you will be able toβ¦- Describe clinically important plasma enzymes and their diagnostic applications.
- Explain the components and interpretation of liver function tests (LFTs).
- Explain the components and interpretation of renal function tests.
- Describe correct specimen collection and pre-analytical variables for blood and urine samples.
- Describe general laboratory techniques, SOPs and safety measures.
Clinical Story
Why This MattersA 52-year-old man with long-standing alcohol use presents with yellowing of the eyes and fatigue. The physician orders a full liver function panel. The lab technologist must know that a raised GGT together with AST>ALT strongly suggests alcohol-related liver injury, and must ensure the bilirubin critical value is communicated promptly.
Core Concepts
Functional plasma enzymes such as lipoprotein lipase, pseudocholinesterase and coagulation proenzymes perform physiological functions in blood; most are synthesised in the liver. Non-functional plasma enzymes leak from damaged tissue and are used diagnostically:
- ALT (Alanine aminotransferase): mainly hepatic; higher in hepatocellular disorders than obstructive ones. Normal: Male <45 U/L, Female <34 U/L.
- AST (Aspartate aminotransferase): liver, skeletal muscle, heart, erythrocytes; rises 6β8h after AMI, peaks 24h. Normal: Male <35 U/L, Female <31 U/L.
- Ξ±-Amylase: pancreatic and salivary origin; small enough to pass into urine; elevated in acute pancreatitis. Normal: 28β100 U/L.
- Lipase: pancreas-specific; elevated in acute pancreatitis and pancreatic carcinoma. Normal: 40β200 U/L.
- GGT (Ξ³-glutamyl transferase): marker of alcohol abuse and hepatobiliary disease; higher in men. Normal: Male <55 U/L, Female <38 U/L.
- LDH (Lactate dehydrogenase): widely distributed, non-specific marker of cell damage; useful with isoenzymes. Normal: 180β360 U/L.
The hepatic function panel typically evaluates ALT, AST, ALP, total and direct bilirubin, albumin and total protein. Bilirubin, a haemoglobin breakdown product, rises in liver disease causing jaundice. Total bilirubin: 0.1β1.0 mg/dL; direct bilirubin: 0.0β0.3 mg/dL; critical adult value: >1.2 mg/dL (newborn: >15 mg/dL). Albumin, the major protein synthesised by the liver, falls when hepatic synthetic function is impaired (normal: 3.2β5.4 g/L).
Renal function is assessed with urine tests (routine urinalysis, creatinine clearance, urea clearance, urine osmolality, urine protein) and blood tests (BUN, creatinine, uric acid). Creatinine clearance is a specific measure of glomerular filtration since creatinine is filtered at a constant rate proportional to muscle mass and is not reabsorbed. Normal creatinine clearance: 90β139 mL/min (males <40y), 80β125 mL/min (females <40y), decreasing ~6.5 mL/min per decade after 40. Normal BUN: 8β20 mg/dL; creatinine: 0.8β1.2 mg/dL (male), 0.6β0.9 mg/dL (female).
Correct venous blood collection requires meticulous skin disinfection (10% povidone iodine or 70% isopropyl alcohol applied concentrically), avoiding re-palpation after disinfection, prompt labelling, and safe sharps disposal. Blood culture bottles and tubes should be transported upright, cushioned to prevent haemolysis, and processed within 24 hours where possible.
Midstream urine collection minimises contamination from urethral and skin organisms; samples should reach the laboratory within 2β3 hours, or be refrigerated at 4β8 Β°C if delayed, in leak-proof containers.
Every laboratory should maintain calibrated equipment, an equipment log book, and readily available Standard Operating Procedures (SOPs) describing who can perform each test, the analytical steps, and safety precautions. Safety measures include documented safety policies, hand hygiene and PPE, eye-wash facilities, biohazard labelling, and trained response to spills, fires and gas leaks, with accident/incident records reviewed periodically.
Laboratory Principle
Most clinical enzyme assays are kinetic photometric methods: the enzyme in the patient's serum catalyses a reaction whose product (or the disappearance of a co-substrate such as NADH) is measured at a specific wavelength over a fixed time interval. The rate of absorbance change is directly proportional to enzyme activity, allowing the result to be reported in international units per litre (U/L).
Equipment Required
Reagents & Materials
| Reagent / Material | Concentration / Grade | Purpose | Storage |
|---|---|---|---|
| ALT/AST kinetic reagent kit | IFCC-standardised | Aminotransferase assay | 2β8 Β°C |
| Diazo reagent | Working reagent | Bilirubin (van den Bergh reaction) | 2β8 Β°C, protect from light |
| Jaffe / enzymatic creatinine reagent | Working reagent | Serum/urine creatinine | 2β8 Β°C |
| 70% isopropyl alcohol / 10% povidone iodine | Antiseptic grade | Skin disinfection before venepuncture | Room temperature |
Step-by-Step Procedure
Apply tourniquet briefly, disinfect the site concentrically, and perform venepuncture without re-palpating the cleaned area.
Transfer blood into the correct tube (plain for most chemistry tests), label immediately with the patient identifier, and transport upright.
Allow to clot 20β30 minutes, centrifuge at 3000β4000 rpm for 10 minutes, and separate serum promptly to avoid analyte degradation.
Load serum onto the automated analyzer for the requested enzyme/chemistry panel; the instrument performs kinetic or endpoint measurement automatically.
Check results against QC and delta-check history before releasing; flag critical values for immediate clinician notification.
Flow Diagram
Quality Control
Run normal and abnormal control sera at the start of each shift and after every calibration or reagent lot change; apply Levey-Jennings/Westgard rules and document all corrective actions.
Enrol in a recognised EQAS/proficiency testing scheme for clinical chemistry and review the performance report each cycle to identify systematic bias against peer laboratories.
Reference Values
Normal Rangesβ οΈ Reference ranges may vary between laboratories. Always apply your laboratory's established reference intervals.
Clinical Interpretation
| Finding | Possible Significance | Action / Follow-up |
|---|---|---|
| ALT >> AST, both elevated | Hepatocellular injury (e.g. viral hepatitis) | Order viral hepatitis serology |
| AST > ALT with raised GGT | Alcohol-related liver injury | Correlate with alcohol history; monitor trend |
| Raised ALP with normal transaminases | Cholestatic/obstructive or bone pathology | Fractionate ALP or check GGT to localise source |
| Raised BUN and creatinine | Renal impairment | Calculate eGFR; correlate with urine output |
| Raised amylase and lipase | Acute pancreatitis | Urgent clinical correlation and imaging |
Common Errors & How to Avoid Them
Cause: Intracellular LDH, AST and potassium leak into serum on red cell lysis, causing falsely high results.
Prevention: Use gentle technique, correct needle gauge, and reject grossly haemolysed samples.
Cause: Prolonged contact of serum with cells alters glucose, potassium and enzyme levels.
Prevention: Centrifuge and separate serum within the recommended time window (usually within 1β2 hours).
Cause: Some anticoagulants interfere with specific chemistry assays.
Prevention: Always confirm the correct tube colour/additive for each requested test before collection.
Laboratory Tips from the Bench
A raised GGT alone, without hepatocellular damage, should never be used to label a patient as an alcoholic β always correlate with the full clinical picture.
Amylase is small enough to be filtered by the glomerulus, so urinary amylase can help differentiate macroamylasaemia from true pancreatitis.
Remember "AST is in the heArt and muscle Too" β AST is less liver-specific than ALT because it is also found in cardiac and skeletal muscle.
Important Notes
A bilirubin greater than 1.2 mg/dL in an adult (or >15 mg/dL in a newborn) is a critical value requiring immediate physician notification.
Standard Operating Procedures can only be modified with the approval of the laboratory quality manager or Head of Laboratory, and must always be readily available at the bench.
Interactive Quiz
Test Your KnowledgeFlashcards
Tap to flipClick or tap any card to reveal the answer.
Clinical Case Study
Apply Your KnowledgeLong-standing heavy alcohol use, presenting with yellowing of the sclera and generalised fatigue for two weeks.
An AST:ALT ratio greater than 1 with a markedly elevated GGT and raised bilirubin, in a patient with a heavy alcohol history, is a classic pattern of alcohol-related hepatocellular injury.
- βAST>ALT is characteristic of alcoholic liver disease, unlike viral hepatitis where ALT>AST.
- βGGT alone should never label a patient an alcoholic without clinical correlation.
- βElevated bilirubin above 1.2 mg/dL is a critical value requiring urgent communication.
Frequently Asked Questions
Recent food intake can transiently alter glucose, triglycerides and some enzyme levels, so fasting reduces variability and ensures results reflect the patient's baseline state.
In macroamylasaemia, amylase binds to plasma proteins forming a complex too large to be filtered by the glomerulus, so urinary amylase is inappropriately low relative to a high plasma amylase.
An SOP ensures every test is performed the same way regardless of the operator, improving consistency, training, safety and traceability of results.
Quick Revision
10-Minute ReviewKey Takeaways
- Plasma enzyme patterns (ALT, AST, GGT, ALP, amylase, lipase, LDH) point to specific organ pathology.
- Liver function tests evaluate hepatocellular integrity, biliary flow and synthetic function.
- Renal function tests evaluate glomerular filtration and tubular function using blood and urine markers.
- Correct specimen collection is essential to obtain a reliable laboratory result.
- SOPs and documented safety practices are core to a compliant, high-quality laboratory.
- Critical values must be recognised and communicated urgently.
Competency Checklist
Track Your MasteryReferences
- Vasudevan DM, Sreekumari S, Vaidyanathan K. Textbook of Biochemistry for Medical Students. 8th ed.
- Burtis CA, Ashwood ER, Bruns DE. Tietz Textbook of Clinical Chemistry.
- NIOS Medical Laboratory Technology curriculum β Biochemistry Module, Lesson 13: Clinical Biochemistry.