Pathology

Cellular Hypertrophy: Mechanisms, Physiologic and Pathologic Types, Cardiac Remodelling and Clinical Consequences Hypertrophy is an increase in the size of individual cells, producing enlargement of the affected tissue or organ. It occurs when cells synthesise more structural proteins, cytoplasmic organelles and functional machinery in response to increased workload, mechanical stretch or trophic signalling. Hypertrophy is especially important in cardiac and skeletal muscle, where mature cells have limited ability to divide. It can preserve function when the stimulus is appropriate, but persistent hypertrophy can consume the oxygen reserve, cause fibrosis and progress to organ failure. Core distinction: hypertrophy increases cell size; hyperplasia increases cell number. An organ can enlarge through both, but the dominant mechanism depends on whether its cells can proliferate. Learning outcomes Define cellular hypertrophy and distinguish it from hyperplasia, dilation, pseudohypertrophy and neoplasia. Explain mechanotransduction, growth-factor, neurohormonal and metabolic pathways that produce hypertrophy. Compare physiologic versus pathologic hypertrophy and pressure versus volume overload. Describe cardiac, skeletal-muscle, smooth-muscle, renal and endocrine examples. Recognise when adaptive hypertrophy becomes maladaptive through ischaemia, fibrosis, electrical instability or pump failure. Interpret clinical findings, ECG/imaging patterns and treatment principles in hypertrophic remodelling. 1. Definition and related terms Term Definition How it differs from hypertrophy Hypertrophy Increase in individual cell size from increased synthesis of proteins and organelles. The defining change is cell enlargement, not primarily cell multiplication. Hyperplasia Increase in cell number through proliferation of cells capable of division. May accompany hypertrophy in tissues such as uterus; absent or limited in mature cardiac myocytes. Dilation Expansion of a cavity or organ, often due to volume load, wall thinning or failure. A dilated chamber may have enlarged cells, but dilation describes geometry, not the cellular mechanism. Pseudohypertrophy Apparent organ enlargement from fat, connective tissue, oedema or abnormal material rather than functional cell enlargement. Examples include muscular dystrophy with fatty replacement and organ enlargement from infiltration. Remodelling Integrated change in cell size, extracellular matrix, chamber geometry, vascularity and function after stress or injury. Hypertrophy is one component of remodelling. Neoplasia Clonal, autonomous abnormal proliferation. Hypertrophy remains stimulus-responsive and regulated; neoplasia is not a normal adaptive response. 2. Why cells hypertrophy The cell must increase its work output or tolerate a new physical/chemical environment. A sustained stimulus changes gene expression, cytoskeletal tension, protein synthesis and organelle content. The response includes both a proximal signal (for example stretch or angiotensin II) and a transcriptional programme that determines the phenotype. Stimulus Sensor/signalling Cellular response Increased mechanical load Integrins, focal adhesions, cytoskeleton, stretch-activated channels, YAP/TAZ, MAPK and calcium signalling. More contractile proteins, sarcomeres, mitochondria and structural support. Growth factors IGF-1/PI3K–AKT–mTOR, RAS–RAF–ERK and related receptor pathways. Increased translation, ribosome production, organelle biogenesis and cell volume. Neurohormonal stimulation Angiotensin II, endothelin, catecholamines and aldosterone with G-protein and kinase signalling. Growth plus extracellular-matrix synthesis, inflammation and fibrosis when chronic. Metabolic demand AMPK, mTOR, mitochondrial and redox sensors. Adjustment of ATP-generating machinery; excessive demand may produce oxidative stress. Hormonal trophic stimulation Oestrogen, TSH, ACTH or other receptor-dependent signals in target tissues. Increased functional organelle and protein mass; hyperplasia may coexist if cells can divide. 3. Molecular programme of hypertrophy 3.1 Protein synthesis and mTOR Growth-factor and nutrient signals activate PI3K–AKT–mTOR, increasing translation initiation, ribosomal biogenesis and synthesis of contractile/cytoskeletal proteins. This is prominent in physiologic skeletal-muscle growth. In pathologic cardiac hypertrophy, parallel calcium–calcineurin–NFAT and MAPK programmes may produce a different, less efficient phenotype. 3.2 Mechanotransduction Mechanical stress changes integrin tension, Z-disc signalling, titin strain, focal adhesions and stretch-sensitive ion channels. These signals alter transcription factors and fetal/embryonic gene programmes. The cell is not merely “swollen”; it is actively rebuilding its contractile and structural machinery. 3.3 Calcium, calcineurin and NFAT Sustained calcium signalling activates calcineurin, which dephosphorylates NFAT and allows nuclear entry. NFAT cooperates with other factors to increase hypertrophic gene expression. This pathway links abnormal workload to structural remodelling and is particularly relevant in pressure-overloaded myocardium. 3.4 Mitochondria and energetics More contractile work requires more ATP. Mitochondria may initially increase in number and oxidative capacity, but capillary growth and mitochondrial adaptation may lag behind cell growth. The resulting oxygen mismatch promotes reactive oxygen species, impaired relaxation, myocyte injury and fibrosis. 3.5 Extracellular matrix Fibroblasts respond to angiotensin II, TGF-beta, aldosterone and mechanical stress by producing collagen. Interstitial fibrosis stiffens tissue, separates electrical connections and reduces microvascular reserve. In cardiac hypertrophy, fibrosis is a major reason that a thick wall can become a poorly compliant and arrhythmogenic wall. 4. Physiologic versus pathologic hypertrophy Feature Physiologic hypertrophy Pathologic hypertrophy Stimulus Exercise, pregnancy, normal growth or a controlled trophic signal. Hypertension, valvular disease, chronic hypoxia, endocrine excess or abnormal loading. Signalling Predominantly IGF-1/PI3K–AKT–mTOR with coordinated vascular support. Mechanical stress, angiotensin II, endothelin, catecholamines, calcium-dependent and inflammatory pathways. Architecture Proportionate growth with preserved or improved function. Disproportionate growth, fibrosis, altered geometry and reduced reserve. Capillary/mitochondrial support Usually matched to workload. May fail to match growth, causing relative ischaemia and oxidative stress. Reversibility Regresses when the stimulus stops, such as after detraining. May regress after cause control, but fibrosis and myocyte loss can persist. Outcome Increased functional capacity. Diastolic/systolic dysfunction, arrhythmia, ischaemia, failure or sudden death risk in selected disorders. The terms “athlete’s heart” and “pathologic hypertrophy” cannot be assigned from wall thickness alone. Symptoms, blood pressure, family history, ECG, chamber geometry, diastolic function and imaging are needed. 5. Cardiac hypertrophy: the major clinical model 5.1 Pressure overload and concentric hypertrophy Pressure overload increases systolic wall stress. The ventricle adds sarcomeres in parallel, thickening the wall and initially reducing wall stress. Common causes include chronic hypertension, aortic stenosis and some congenital outflow obstructions. Early compensation Progressive maladaptation Thicker wall generates pressure with less wall stress. Increased muscle mass raises oxygen demand and compresses intramyocardial vessels. Stroke volume is initially preserved. Stiff ventricle relaxes poorly; filling pressures rise and pulmonary congestion develops. Contractile proteins and mitochondria increase. Capillary and mitochondrial supply may lag, causing subendocardial ischaemia and myocyte death. Neurohormonal support maintains output. Angiotensin, aldosterone and TGF-beta drive fibrosis, remodelling and electrical instability. 5.2 Volume overload and eccentric remodelling

Physiologic Stresses and Cellular Adaptations: How Cells Survive, Remodel and Fail Cells constantly adjust to changing workload, hormones, nutrients, oxygen, temperature, mechanical forces and environmental injury. A cellular adaptation is a reversible change in cell size, number, phenotype, metabolism or function that allows a viable cell to reach a new steady state when its environment changes. Adaptation is not the same as health: it may protect the cell initially, but persistent or excessive stress can exceed the adaptive reserve and progress to cell injury, cell death, fibrosis or neoplasia. Core pathology sequence: normal homeostasis → physiologic or pathologic stress → adaptive response → new steady state if the stress is tolerable → injury when the stress is severe, prolonged or unrelieved. Removing the stimulus may allow return toward baseline, but some changes leave a risk of recurrence or malignant transformation. Learning outcomes Define cellular stress, homeostasis, adaptation, injury and decompensation. Classify physiologic and pathologic stresses and explain how intensity, duration, cell type and reserve determine the outcome. Distinguish hypertrophy, hyperplasia, atrophy and metaplasia by mechanism, morphology and examples. Explain the roles of nutrient/growth-factor signalling, mechanotransduction, autophagy, the unfolded-protein response, antioxidant responses and proteostasis. Recognise dysplasia as disordered growth rather than a classic protective adaptation and understand its relationship to cancer risk. Apply the concepts to hypertension, pregnancy, disuse, airway irritation, liver adaptation, endocrine stimulation and clinical emergencies. 1. Homeostasis and cellular stress Homeostasis is the regulated maintenance of an internal environment compatible with cell survival. Each cell has a limited adaptive reserve determined by its differentiation, blood supply, energy stores, antioxidant capacity, ability to divide and capacity to repair damaged molecules. Term Meaning Clinical implication Physiologic stress An increased demand or normal hormonal signal that remains within an organised biologic range. Exercise increases skeletal-muscle workload; pregnancy stimulates uterine growth; adaptation is usually coordinated and reversible. Pathologic stress An abnormal, excessive, persistent or damaging stimulus. Hypertension overloads the left ventricle; smoking irritates bronchi; obstruction causes pressure-related remodelling. Adaptation A viable cell changes structure, function, metabolism or phenotype to tolerate the stress. May preserve function, but the new state can eventually become harmful. Cell injury The stress exceeds adaptive capacity, causing biochemical and structural dysfunction. Early injury may be reversible; severe or persistent injury can become irreversible. Decompensation Adaptive mechanisms can no longer maintain function. Hypertrophied myocardium develops ischaemia and failure; an exhausted beta-cell cannot maintain insulin output. 2. What determines the response? Determinant Examples Why it changes the outcome Type of cell Neurons and cardiac myocytes have limited replication; hepatocytes and many epithelia can proliferate. Post-mitotic cells generally enlarge or alter metabolism rather than increase cell number. Intensity and duration Brief exercise versus years of uncontrolled hypertension. A mild, short stimulus may be fully reversible; chronic stress may cause fibrosis, exhaustion or mutation. Oxygen and blood supply Renal medulla versus well-perfused cortex; anaemia or shock. Low oxygen limits ATP production and narrows the adaptive reserve. Nutrient and energy status Starvation, diabetes, obesity, mitochondrial disease. AMPK and mTOR balance catabolism and growth; energy shortage favours conservation/atrophy. Growth factors and hormones Insulin, IGF-1, oestrogen, TSH, erythropoietin, catecholamines. Receptors and downstream signals alter protein synthesis, proliferation or differentiation. Mechanical forces Pressure overload, stretch, shear stress, immobilisation. Integrins, cytoskeleton, ion channels and YAP/TAZ-linked pathways convert force to gene expression. Genetic background and prior injury Inherited enzyme defects, viral injury, previous infarction. Repair capacity, antioxidant reserve and baseline tissue architecture differ between patients. 3. Main forms of cellular adaptation Adaptation Primary change Typical stimulus Classic examples Hypertrophy Increase in individual cell size; organ enlarges without a primary increase in cell number. Increased workload, pressure/volume load, trophic hormones. Left-ventricular hypertrophy in hypertension; skeletal-muscle enlargement with resistance exercise; uterine smooth-muscle hypertrophy in pregnancy. Hyperplasia Increase in cell number by proliferation of cells capable of division; often accompanied by hypertrophy. Hormonal or growth-factor stimulation, compensatory demand, chronic irritation. Endometrial proliferation, liver regeneration, benign prostatic hyperplasia, callus-related epithelial proliferation. Atrophy Decrease in cell size and often organ mass and function; may involve fewer cells. Reduced workload, denervation, ischaemia, malnutrition, loss of endocrine stimulation, ageing. Muscle wasting in immobilisation; brain atrophy after chronic ischaemia; endometrial atrophy after menopause. Metaplasia Reversible replacement of one mature, differentiated cell type by another better able to tolerate the stress. Chronic irritation, inflammation, vitamin deficiency or altered signalling. Smoking-related ciliated columnar-to-squamous change; gastric/intestinal metaplasia; Barrett oesophagus. These categories can overlap. A tissue may enlarge through both hypertrophy and hyperplasia, and atrophy may combine reduced cell size, loss of cells and decreased function. Metaplasia is not the direct conversion of one mature cell into another; it usually reflects reprogramming of local stem/progenitor cells and altered differentiation. 4. How adaptation is switched on 4.1 Receptors and signal transduction Hormones, cytokines, growth factors and mechanical stimuli bind receptors or alter membrane/cytoskeletal tension. Signalling through PI3K–AKT–mTOR promotes protein synthesis and growth; RAS–RAF–MEK–ERK promotes proliferation; JAK–STAT transmits cytokine and hormone signals; calcium–calmodulin and calcineurin can reprogramme contractile cells. The resulting transcription factors alter thousands of genes rather than one isolated protein. 4.2 Mechanotransduction Stretch and pressure are sensed by integrins, focal adhesions, the cytoskeleton, ion channels and junctional complexes. Signals converge on YAP/TAZ, MAPK, calcium and growth-factor pathways. This explains why a chronically pressure-loaded ventricle enlarges and why reduced loading of a limb causes muscle loss. 4.3 Metabolic sensors mTOR: favours growth and protein synthesis when nutrients and growth factors are abundant; excessive activation contributes to pathologic growth. AMPK: senses low cellular energy and promotes ATP-generating pathways while restraining energy-consuming growth. HIF: responds to low oxygen and induces genes for glycolysis, angiogenesis and erythropoietic signalling. Nrf2: increases antioxidant and detoxification genes when reactive electrophiles/oxidants rise. UPR sensors (PERK, IRE1, ATF6): reduce translation and increase chaperones when misfolded proteins accumulate in the endoplasmic reticulum. 4.4 Proteostasis and quality control Cells continuously balance protein synthesis, folding, trafficking, ubiquitin–proteasome degradation and autophagy. When damaged proteins or organelles accumulate, selective removal can preserve viability. If the burden is excessive, these same stress pathways can contribute to apoptosis or other forms of cell death. 5.

Specimen Transportation: Safe Packaging, Cold Chain, Timing, Documentation and Quality Assurance Specimen transportation is the controlled movement of a clinical or pathology specimen from the point of collection to the testing laboratory while protecting the specimen, the patient, the carrier, the public and the environment. It is not simply “sending a sample.” The route must preserve the requested biological target, maintain the validated temperature and time window, prevent leakage or contamination, provide traceability and comply with biosafety and dangerous-goods rules. Golden rule: a specimen is only as good as the whole pre-analytical chain. Correct collection and preservation can still be defeated by a wrong route, a delayed rider, a broken cold chain, inadequate packaging, missing paperwork or a specimen delivered to the wrong laboratory. Learning outcomes After studying this post, the emergency medicine or laboratory student should be able to: Plan an appropriate transport route for blood, urine, stool, respiratory specimens, CSF, body fluids, tissue, cytology and referral samples. Explain the difference between internal hand transport, local courier transport and regulated shipment of infectious substances. Apply the primary receptacle–secondary packaging–rigid outer packaging principle and select absorbent, cushioning and temperature-control materials. Classify specimens conceptually as Category A, Category B, exempt human/animal specimen or another regulated material, and know when to stop and seek trained advice. Complete labels, request forms, temperature records, chain-of-custody documents and referral notifications. Respond safely to a spill, leakage, lost package, temperature excursion, delay or rejected specimen. 1. Why transport is a patient-safety process Transport objective What it means in practice Failure if ignored Biological integrity Use the validated time, temperature, light protection, medium and orientation for the requested test. Cell lysis, bacterial overgrowth, loss of viability, nucleic-acid degradation, altered chemistry or autolysis. Containment Use leak-proof, correctly closed receptacles, absorbent material and intact secondary/outer packaging. Exposure of staff, riders, patients and the environment; cross-contamination. Traceability Record patient identifiers, specimen source, collection time, dispatch/receipt time, sender, courier, destination and condition. Wrong-patient result, inability to investigate a delay or lost specimen. Timeliness Choose a route that meets the stability window and communicates urgency. Missed emergency diagnosis, invalid culture, altered blood gas or deteriorated CSF. Regulatory compliance Classify, package, mark, label and document according to current national and international rules. Unsafe shipment, legal breach, refusal by carrier or incident during transport. Continuity Use backup power, cool boxes, validated data loggers and contingency plans for traffic, weather, equipment or courier failure. Cold-chain loss and a specimen that cannot be replaced. The WHO Laboratory Quality Stepwise Implementation tool expects laboratories to define safe, timely and temperature-appropriate transport, and to monitor the process rather than assuming that a package arrived in good condition. The 2025 WHO guidance on infectious-substance transport also emphasises classification, packaging, marking, labelling, documentation, refrigeration and trained personnel. 2. Transport planning: the five questions What is the exact test and destination? Confirm whether the specimen is for chemistry, haematology, coagulation, microbiology, histopathology, cytology, immunology, molecular testing or a referral laboratory. What is the validated stability window? Record the collection time and the latest acceptable receipt/processing time. Critical specimens such as blood gas, CSF for meningitis, fresh tissue for flow or cultures require an urgent route. What temperature and physical conditions are required? Choose controlled ambient, refrigerated, frozen or another validated condition. “Put it on ice” is not a complete instruction. What is the biosafety and regulatory classification? Assess whether the material is Category A, Category B, exempt human/animal specimen or another dangerous good. If unsure, consult a trained biosafety/transport officer before dispatch. Who accepts responsibility at every hand-off? Confirm sender, courier, receiving laboratory and an after-hours contact. A specimen should never travel with no named destination or no way to report a delay. 3. Internal transport within a health facility 3.1 Preparing a specimen for a ward-to-laboratory journey Verify two patient identifiers against the request form at collection and again before dispatch. Label the primary receptacle immediately; include specimen type/site, date and time, and collector details as required. Close the cap securely and check for cracks, leakage, external contamination and adequate volume. Place the receptacle upright in a rigid, washable, closable transport box or leak-proof secondary container with absorbent material. Keep request forms in a separate dry compartment or pouch; never wrap paperwork around a potentially contaminated tube. Use a dedicated route. Do not carry open tubes in pockets, hand, food trays, public lifts without containment or ordinary paper envelopes. Deliver urgent samples by hand or the approved rapid system; follow local policy for pneumatic tube restrictions. At receipt, document time, condition, temperature where required and any discrepancy. Obtain a second sample when the first is unsuitable. 3.2 Pneumatic tube systems Pneumatic transport is facility-specific. It may be unsuitable for blood gases, blood cultures, fragile tubes, large tissue containers, CSF, specimens for platelet function or tests affected by vibration, pressure, delay or leakage. The laboratory and clinical service should validate which specimen types can travel in the system; a general assumption that “all blood can go by tube” is unsafe. 4. The triple-packaging system For infectious or potentially infectious material transported outside the immediate controlled area, the standard concept is three layers. National and international rules specify exact performance requirements, so training and a compliant package are essential. Layer Purpose Requirements and examples Primary receptacle Holds the specimen. Leak-proof tube, vial, bottle, swab tube or sealed tissue container. Use a screw cap or closure that remains secure. Wrap or separate multiple receptacles to prevent breakage and contact. The label must remain readable. Absorbent and cushioning Contains liquid if the primary receptacle leaks and protects it from shock. Enough absorbent material to take up the entire liquid volume; separate glass/fragile tubes; use cushioning that does not compromise closure or temperature. Secondary packaging Provides an additional leak-proof or sift-proof barrier. Rigid or flexible certified secondary container, sealed bag or canister as permitted. Place request paperwork outside the contaminated compartment. Include temperature-control material in the correct location. Rigid outer packaging Protects the package during handling and carries marks/labels. Strong, appropriately sized outer box

Specimen Preservation: Fixation, Stabilisation, Storage, Temperature and Quality Control Specimen preservation is the deliberate use of time, temperature, chemical fixatives, anticoagulants, transport media and other controls to keep a patient specimen as close as possible to its biological state until the requested examination is completed. Preservation is part of the pre-analytical phase; a perfectly performed assay cannot repair a specimen that was allowed to clot, haemolyse, dry, warm, freeze, autolyse, grow contaminating organisms or lose its cellular and molecular targets. Clinical safety principle: preservation is always test-specific. The correct condition for a culture may be harmful for a chemistry, cytology, coagulation, molecular or histology test. When a local laboratory SOP, referral laboratory or kit insert gives a different validated condition, follow that instruction, document it and do not improvise. Learning outcomes By the end of this lesson, a student should be able to: Define preservation and distinguish it from collection, transport, storage, fixation, stabilisation and processing. Choose an appropriate container, additive, preservative, temperature and maximum delay for common clinical specimens. Explain why blood, urine, stool, respiratory specimens, CSF, body fluids, tissue and cytology require different handling. Recognise when refrigeration, freezing, light protection, anticoagulation or immediate processing is required—and when it is contraindicated. Identify compromised specimens, record the effect on results, communicate with the clinician and apply laboratory acceptance/rejection policy. 1. Where preservation fits in the laboratory pathway Stage What must be controlled Typical failure Clinical consequence Clinical request Correct test, indication, specimen, timing and urgency “Blood test” without a defined test or timing Wrong container or un-interpretable result Collection Patient identity, asepsis, volume, tube order, site and timing Underfilled citrate tube; contaminated culture; wrong tube Clotting error, false-positive culture or rejection Initial preservation Correct additive/fixative, prompt mixing, protection from light or evaporation EDTA tube not mixed; tissue left dry; bilirubin exposed to light Clots, autolysis, analyte loss or poor morphology Transport Sealed secondary packaging, temperature, time, orientation and biosafety Leaking package, prolonged heat or inappropriate ice Danger to staff and unreliable results Receipt and processing Identification, integrity, volume, time, condition and suitability for each test Unlabelled or haemolysed specimen accepted without comment Result assigned to wrong patient or analytically biased Short/long-term storage Validated retention temperature, aliquots, monitoring and traceability Repeated freeze–thaw or unrecorded freezer failure Loss of diagnostic material and inability to verify a result The World Health Organization quality approach requires each laboratory to define written, test-specific instructions for collection, preservation, transport, acceptance, storage and disposal. A temperature label such as “keep cold” is not enough: the SOP should state the permitted range, time window, container, additive and action after a deviation. 2. Key preservation concepts Term Meaning Examples Important caution Fixation Irreversible chemical or physical preservation of cells/tissue, stopping autolysis and maintaining morphology. 10% neutral buffered formalin for routine histology; alcohol fixation for some cytology; glutaraldehyde for electron microscopy. Fixation prevents many downstream tests. Never place tissue intended for culture, flow cytometry, cytogenetics or many molecular assays in formalin unless the assay is validated for fixed material. Stabilisation Slowing or preventing change in an analyte, nucleic acid, cell or organism without necessarily fixing it. Fluoride-containing tube for glycolysis inhibition; RNA stabilisation reagent; validated urine preservative. Stabilisers are not interchangeable and can interfere with other assays. Anticoagulation Preventing clot formation so plasma, whole blood or cells remain available. EDTA for CBC; sodium citrate for coagulation; heparin for many plasma chemistry tests. The anticoagulant-to-blood ratio and correct mixing are essential; a clotted sample is not repaired by remixture. Transport medium Maintaining viability or nucleic-acid integrity during transit while limiting overgrowth or desiccation. Cary–Blair for enteric bacteria; viral/UTM medium for respiratory swabs; Amies medium for selected bacterial swabs. Transport medium is selected for the organism and test. It is not a general-purpose preservative. Cryopreservation Freezing at a validated temperature to slow degradation for later testing. Aliquoted serum/plasma, selected molecular specimens, viable cells with a cryoprotectant. Freeze–thaw cycles, frost-free freezers and poorly controlled thawing can destroy analytes or cells. Storage/retention Keeping a processed or unprocessed specimen for a defined period under monitored conditions. Retained serum, paraffin blocks, slides, residual urine or microbiology isolates. Retention duration is a local regulatory/SOP decision; it depends on specimen type, test, risk and clinical need. 3. Universal rules before preserving any specimen Confirm the test menu and urgency. Ask which discipline will examine it—chemistry, haematology, coagulation, microbiology, histopathology, cytology, immunology or molecular diagnostics. The same specimen may need separate portions. Identify the patient at the bedside. Use the required identifiers, label immediately and record collection date/time, collector, source/site, relevant treatment and time-sensitive clinical information. Use the validated container. Check tube colour, additive, expiry, sterility, volume, lot where required and compatibility with the analyzer or referral laboratory. Preserve promptly. Mix additive tubes by gentle inversion as specified; do not shake. Start fixation, cooling, light protection or transport-media placement at once. Protect specimen quality. Prevent haemolysis, clotting, evaporation, desiccation, contamination, dilution, exposure to oxygen or light, and contact with unsuitable surfaces. Separate when necessary. Centrifuge and aliquot serum/plasma only according to the validated SOP. Use clean, leak-proof, labelled aliquots to avoid repeated opening and freeze–thaw. Document deviations. If time, temperature, volume, container or integrity is outside limits, do not silently proceed. Consult the laboratory, record the limitation, and recollect when a valid result is not possible. Preserve safety as well as accuracy. Treat all unfixed specimens as potentially infectious. Use leak-proof primary and secondary packaging, absorbent material and appropriate PPE. Do not overgeneralise “refrigerate.” Refrigeration slows many chemical reactions but can damage cells, precipitate proteins, alter platelet function, reduce recovery of some organisms or change pH. A specimen for culture, CSF cell count, blood gas, cryoprotein, cold agglutinin or a specialised molecular assay may need a different condition. 4. Blood specimens 4.1 Whole blood and anticoagulant selection Specimen/handling Common use Preservation logic Errors to avoid EDTA whole blood (lavender/purple) Full blood count, blood film, reticulocytes, HbA1c and selected molecular/flow tests EDTA chelates calcium and preserves cellular morphology for a limited, test-specific period. Mix gently immediately after collection. Clots