GC158 Point-of-care Testing (POCT)
Point-of-care testing is diagnostic testing performed at or near the site of patient care, outside the central laboratory, to provide rapid results that facilitate immediate clinical decision-making.
Point-of-Care Testing (POCT)
This lecture (GC 158) covers the principles, advantages, limitations, quality requirements, and clinical applications of Point-of-Care Testing (POCT) – laboratory tests performed at or near the site of patient care to enable rapid clinical decision-making. The lecture is Chemical Pathology-heavy and directly examinable in MCQ and SAQ formats. It connects to multiple other GC and CFB lectures: DM management (glucometers), pregnancy (urine hCG), drug screening, blood gas analysis, urine dipstick interpretation, and laboratory interferences.
Learning Objectives (Inferred from Slide Content)
- Define POCT and understand its rationale.
- List the general considerations for governance of POCT (SOP, training, QA, QC, EQA, documentation, maintenance, safety).
- Enumerate advantages and desirable characteristics of POCT devices.
- Know the common examples of POCT in clinical practice.
- Interpret urine dipstick results, including false positives/negatives.
- Understand the urine pregnancy test – mechanism, hCG variants, causes of elevated hCG, false positives.
- Understand the blood glucose meter – methods, interferences (especially GDH-PQQ), limitations in altered perfusion and at extreme values, and when laboratory confirmation is required.
- Know the basics of POCT blood gas analysis – specimen handling, timing, avoiding pre-analytical errors.
- Know about drug-of-abuse testing as POCT.
"Any test performed at the time at which the test result enables a decision to be made and an action taken that leads to an improved health outcome." — Tietz (as cited in GC 158 slide) [1]
The CFB lecture (MED10) adds: "POCT is clinical laboratory testing conducted close to the site of patient care where care or treatment is provided. POCT provides rapid turnaround of test results, enabling prompt and timely instigation of appropriate patient management." [2]
Why does POCT exist?
Traditional central laboratory testing follows a long chain: clinician orders test → phlebotomy → specimen transport → specimen receipt/registration → analysis → result authorisation → result communication. Each step adds turnaround time (TAT). In time-critical situations (e.g., hypoglycaemia, DKA, acute MI, massive haemorrhage), waiting for central lab results may delay life-saving interventions. POCT collapses the chain by putting the test where the patient is.
Key Principle
The benefit of POCT is ONLY realised if the result is accurate and reliable. A fast but wrong result is worse than a slow correct one because it may lead to harmful clinical decisions.
The lecture explicitly lists these governance pillars [1]:
| Governance Element | Why It Matters |
|---|---|
| Standard Operating Procedure (SOP) | Ensures every operator performs the test identically – reduces inter-operator variability |
| Training and Certification | Non-laboratorians (nurses, doctors, patients) operate POCT devices; they need formal training to avoid pre-analytical and analytical errors |
| Quality Assurance (QA) | The umbrella term for all activities that ensure test quality |
| Internal Quality Control (IQC) | Running known-value control samples at regular intervals on the device to detect drift/malfunction |
| External Quality Assessment (EQA) | Blinded proficiency testing samples sent by an external body to compare your device's results against other sites – detects systematic bias |
| Documentation and Reporting | Results must be recorded in the patient record; traceability is critical for medicolegal and clinical continuity |
| Identification and traceability | Positive patient identification plus operator ID, device ID, reagent lot/expiry, date/time and result prevent a fast test becoming an untraceable result |
| Maintenance | Regular calibration checks, cleaning, battery/reagent replacement |
| Safety | Sharps disposal (lancets), biohazard handling (blood/urine), infection control |
Exam Trap
Students often forget that POCT devices require the same quality framework as central lab analysers. The fact that a test is "bedside" does NOT excuse it from IQC/EQA requirements.
Standards update: the slide is historical
Slide 7 reproduces ISO 22870:2006. ISO later issued ISO 22870:2016, but both editions are now withdrawn; the ISO catalogue identifies ISO 15189:2022 as the replacement. The practical lesson remains current: POCT sits inside the medical laboratory's quality-and-competence system rather than outside it. [7]
3. Advantages of POCT
Lecture slide: "Benefit is based on the accuracy and reliability of the POCT results." [1]
| Advantage | Explanation |
|---|---|
| Reduced TAT | The single biggest selling point; enables real-time clinical decisions |
| Improved patient management | Faster diagnosis → faster treatment → better outcomes |
| Fewer transport and hand-off steps | The sample need not travel through the central-lab chain, but the order, positive patient ID, operator/device/lot traceability and result documentation remain mandatory |
| Minimised delay in sample collection | Operator collects and tests simultaneously |
| Minimal sample requirement | Finger-prick capillary blood, urine drop – less painful, less volume |
| Reduced transport delay | No pneumatic tube / porter needed |
| Reduced registration delay | No lab log-in step |
| Reduced time entering complex facility | Bypasses multi-step automated analyser queue |
"Transportation – disconnection between time, individual, specimen, laboratory and physician" [1]
Traditional testing introduces a "disconnection": the specimen is separated from the patient and travels a physical and administrative journey. POCT keeps specimen and patient together.
| Feature | Why |
|---|---|
| Portable | Can go to bedside, ambulance, rural clinic |
| Dry, stable, unit-dose device | No liquid reagents to spill/expire; each test strip is self-contained |
| Robust (storage and usage) | Tolerates temperature variation, jostling |
| Simple to use | Non-lab staff can operate reliably |
| Clinically comparable with the reference method | Agreement must be assessed at relevant decision limits; matrix, calibration and method bias can produce predictable differences from a central-lab result |
| Safely operated | Minimal biohazard risk |
| Built-in / integrated calibration / QC | Self-calibrating reduces operator steps and error |
| Ambient storage temp for reagents | No refrigeration needed → simpler logistics |
| Low instrument cost | Cost-effective deployment at scale |
| Record keeping | Electronic connectivity to hospital information system (HIS) for automatic result upload |
From the lecture slide [1]:
| POCT Device | Common Clinical Use |
|---|---|
| Blood gas analysers | ICU, ED, operating theatre – pH, pO₂, pCO₂, HCO₃⁻, lactate, electrolytes |
| Blood gas/electrolyte/metabolite handheld meters | Rapid K⁺ in hyperkalaemia, Na⁺ in hyponatraemia |
| Haemostasis analysers | ACT in cardiac surgery (heparin monitoring), TEG/ROTEM in massive transfusion |
| Cardiac marker analysers | Troponin at bedside in acute chest pain |
| Urine test strips (visual and readers) | UTI screening, proteinuria, glycosuria, ketonuria, haematuria |
| Glycated haemoglobin (HbA1c) analysers | Same-visit diabetes monitoring; diagnostic use depends on an appropriately certified/approved method and the local diagnostic pathway |
| Whole blood glucose and lactate meters | DM monitoring, hypoglycaemia detection, sepsis (lactate) |
| Pregnancy tests | Urine hCG – ED, obstetrics, GP |
| Faecal occult blood | CRC screening |
| HIV testing | Rapid HIV antibody/antigen screening in outreach settings; a reactive screen enters a diagnostic algorithm rather than standing alone |
| Drug-of-abuse testing | ED, occupational health, forensic |
5. Urine Dipstick Testing – Detailed Interpretation
The lecture devotes several slides to urine dipstick analysis. This is a revision topic but highly examinable because it tests understanding of the chemistry behind each pad.
Slides 8–9 show the reagent bottle beside its colour comparator. After briefly immersing the strip, remove excess urine, start the timer, and compare each pad at its specified time under good lighting (or use the validated reader). In the illustrated chart, glucose and bilirubin are read at 30 seconds, ketone at 40 seconds, specific gravity at 45 seconds, most other chemistry pads at 60 seconds, and leukocyte esterase at 2 minutes. These times and even pad order are product-specific: use the current bottle insert, check expiry/storage/desiccant, and never interpret a dried strip later.
The blood pad also carries a visual discriminator: a speckled reaction suggests intact erythrocytes, whereas a uniform colour change reflects free haemoglobin or myoglobin. Dipstick protein is mainly albumin-sensitive, so a negative pad does not exclude light-chain or low-molecular-weight proteinuria.
Principle: Nitroprusside reaction-based methods. Detects Acetoacetate >> Acetone. β-Hydroxybutyrate is NOT measured. [1]
Why this matters clinically:
In diabetic ketoacidosis (DKA), the predominant ketone body is β-hydroxybutyrate (β-OHB), which can comprise up to 75% of total ketones. The urine dipstick uses the nitroprusside (sodium nitroferricyanide) reaction, which reacts with acetoacetate and (weakly) with acetone, but does NOT detect β-OHB at all.
Clinical implication:
- At presentation of severe DKA, the urine dipstick may paradoxically show only moderate ketones because most ketones are β-OHB.
- During treatment of DKA (with insulin and fluids), β-OHB is converted back to acetoacetate. The urine dipstick may then show increasing ketones even as the patient is improving — this is a well-known trap in clinical practice and exams.
- A serum/whole-blood β-OHB meter (also a POCT device) is superior for monitoring DKA.
High Yield – DKA Monitoring Trap
Do NOT use the urine ketone dipstick to monitor DKA treatment progress. The dipstick misses β-hydroxybutyrate and may show "worsening" ketones during successful treatment as β-OHB converts to acetoacetate. Use a blood β-OHB POCT meter instead.
Slide 10 deliberately separates physiology/context from pathology. Examples include transient protein after fever/exercise or orthostatic proteinuria versus renal disease; glycosuria from a lowered renal threshold versus diabetes/Fanconi syndrome; menstrual/exercise blood versus glomerular, stone, tumour or urinary-tract causes. A pad result is therefore a screening observation, not the final diagnosis; confirm persistent or clinically important abnormalities with microscopy and/or quantitative laboratory testing.
The lecture references Patel et al. Pediatr Clin N Am 2006 for a table of false positives and negatives [1]
The lecture references Patel et al. Pediatr Clin N Am 2006 for a table of false positives and negatives [1]
Key examples to know for exams:
| Dipstick Pad | False Positive | False Negative |
|---|---|---|
| Glucose | Strong oxidising agents (e.g., bleach contamination) | High ascorbic acid (vitamin C) intake |
| Protein (albumin) | Highly alkaline urine (pH > 8), concentrated urine, contamination with antiseptics (chlorhexidine) | Dilute urine, non-albumin proteins (Bence Jones protein / light chains in myeloma) |
| Blood / Haemoglobin | Myoglobin (rhabdomyolysis), semen, menstrual contamination, oxidising agents | High ascorbic acid, high specific gravity, captopril |
| Leukocyte esterase | Vaginal contamination, oxidising agents, Trichomonas | High glucose/protein or specific gravity and some drugs; vitamin-C effects are pad/brand dependent |
| Nitrite | Contamination or a specimen standing too long | Organisms that do not reliably reduce nitrate (classically Enterococcus and some staphylococci), low dietary nitrate, frequent voiding/short bladder dwell, dilute urine and some pad-specific chemical interferences |
| Ketones | Captopril, mesna, highly pigmented urine | β-OHB predominance (as in DKA) |
Vitamin C interference is chemistry-dependent
Ascorbic acid is a reducing agent and can cause false-negative glucose, blood or nitrite reactions on susceptible strips. It is not a universal rule for every pad or manufacturer: newer strips may include an iodate layer or a separate ascorbate pad. Resolve a clinic–dipstick mismatch using the current product insert and confirmatory testing.
6. Urine Pregnancy Test (hCG)
Lower limit of detection of urine hCG: 25 mIU/mL (varies in different test kits). Blood hCG concentrations: Non-pregnant < 5 IU/L. [1]
The test uses a lateral flow immunochromatographic assay (a "sandwich" immunoassay):
- Urine is applied to an absorbent pad.
- hCG in the urine binds to colloidal gold-conjugated anti-hCG antibody (mobile phase).
- The hCG–antibody complex migrates along the membrane and is captured by a second anti-hCG antibody immobilised at the test line → visible line appears.
- Excess conjugated antibody migrates further and is captured by an anti-mouse antibody at the control line → visible line confirms the test worked.
- Control line only = negative at that device's detection limit
- Test + control lines = positive; a faint test line read within the manufacturer's time window still counts
- No control line = invalid, irrespective of whether a test line is visible
In pregnancy, hCG immunoreactivity is due to many variants: intact hCG, hCG-h (hyperglycosylated hCG), hCGn (nicked hCG), free β-hCG subunit [found in urine & serum], and hCGcf (core fragment of hCG) [urine only]. [1]
"Different POCT devices may recognise different variants" — "Negative does NOT mean patient is NOT pregnant." [1]
Why this is critical: Each POCT kit uses a particular capture/detection antibody pair, so variant recognition differs. Slide 19 demonstrates this directly: the devices all detected the intact/nicked preparations in that experiment but differed markedly for free β and the urinary β-core fragment. It is therefore unsafe to assume that all devices share one sensitivity profile.
Slide 17 contrasts two sandwich-assay failures:
- High-dose hook effect: an extreme concentration of antigen saturates the mobile and fixed antibodies separately, preventing formation of the labelled antibody–hCG–capture antibody sandwich.
- Hook-like/variant effect: a urinary hCG variant (notably β-core fragment in the cited series) is recognised by one assay antibody but not the other; in excess it occupies one side of the assay and blocks intact hCG sandwich formation.
The five ED cases shown on the slide had negative urine devices despite ultrasound-confirmed pregnancies and serum hCG from about 134,000 to 420,000 IU/L. This is a case series, not a false-negative rate. Dilution can reveal a hook phenomenon in the laboratory, but a clinician with a discordant bedside result should obtain a quantitative serum hCG and appropriate imaging rather than improvising strip dilution. [13]
From lecture slide [1]:
| Cause | Mechanism |
|---|---|
| Normal pregnancy | Trophoblast produces hCG |
| Abnormal pregnancy (ectopic, miscarriage) | Trophoblast tissue present but in abnormal location/state |
| Gestational trophoblastic disease (hydatidiform mole, choriocarcinoma) | Abnormal trophoblast proliferation → very high hCG |
| Germ cell tumours | Non-gestational tumours (e.g., testicular) producing hCG |
| Ectopic hCG-producing tumours (e.g., Ca lung) | Paraneoplastic hCG secretion |
| Pituitary hCG | Low-level hCG-like material from pituitary, especially post-menopause (shares α-subunit with LH/FSH/TSH) |
| Previous injection of hCG (athletes, bodybuilders) | Exogenous hCG for performance enhancement or infertility treatment |
| Immunoassay interferences | Heterophilic antibodies (e.g., HAMA) causing false-positive on lab assay |
| Cross-reactivity with LH | Unlikely with modern 2-site immunometric assays (historical issue) |
From lecture slide [1]:
| Cause of False Positive | Explanation |
|---|---|
| Biochemical pregnancy (very early pregnancy loss) | A true biological hCG signal, not an analytical false positive |
| Missed reaction time / incorrect reading time | Reading the test too late allows non-specific migration → faint "positive" line |
| Drugs (e.g., hCG shot for infertility) | Exogenous hCG in the system |
| Evaporation/indent lines | A dried strip read after the allowed interval may show a colourless/grey line that is misread as positive |
| Mislabelled specimens | Administrative error |
High Yield – Negative UPT ≠ Not Pregnant
A negative urine pregnancy test does NOT definitively exclude pregnancy. Causes include very early testing, dilute urine, device-specific variant recognition and rare hook/hook-like effects. If the clinical consequences matter—pain/bleeding, suspected ectopic pregnancy, teratogenic treatment or imaging—obtain a quantitative serum hCG and follow the clinical/ultrasound pathway. Heterophile-antibody interference is mainly a problem in serum immunoassays; a negative urine result can help the laboratory investigate a persistently low discordant serum hCG.
The lecture shows urine drug-of-abuse POCT devices [1]
These are also lateral flow immunoassay strips, but they work via a competitive inhibition format (opposite to pregnancy tests):
- No drug in urine → labelled antibody–drug conjugate binds to the test line → line appears = NEGATIVE
- Drug present in urine → drug in the sample competes with the conjugate → test line does NOT appear = POSITIVE (i.e., absence of a line is positive)
Important points:
- A visible control line is mandatory. On a competitive card, a faint test line usually still means “below the cutoff”; read the device insert.
- These are presumptive screening tests, not proof of intoxication, dose or timing. Confirm by a validated mass-spectrometric method when the result is disputed or will drive a high-consequence clinical, employment, legal or safeguarding decision. [11]
- Cross-reactivity is common (e.g., pseudoephedrine causing false positive for amphetamines, poppy seeds for opiates).
- Chain of custody and specimen integrity are critical for medicolegal purposes.
8. Blood Glucose Meter (Glucometer)
"To determine the approximate blood glucose by a small drop of blood, pricking from skin by a lancet. The blood is placed on the test strip. For home monitoring of blood glucose in patients with diabetes mellitus and hypoglycaemia." [1]
The lecture lists three enzymatic methods [1]:
| Method | Enzyme | Cofactor | Key Point |
|---|---|---|---|
| Glucose Oxidase (GOx) | Glucose oxidase | O₂ | Glucose-selective, but some electrochemical designs are affected by oxygen tension |
| GDH-PQQ | Glucose dehydrogenase | Pyrroloquinoline quinone | Older non-glucose-specific systems can react with maltose, galactose or xylose |
| GDH-FAD / GDH-NAD | Glucose dehydrogenase | FAD or NAD | Generally more glucose-selective, but safety still depends on the exact strip's validated interference profile and intended use |
The slide abbreviates the interference as “icodextrin or immunoglobulins.” More precisely, maltose produced from icodextrin and maltose present in some immunoglobulin/drug formulations can be misread as glucose by susceptible GDH-PQQ systems. The polymer or immunoglobulin protein itself is not the analyte. [8]
Why is this dangerous?
- Patients on peritoneal dialysis use icodextrin-containing dialysate (e.g., Extraneal). Icodextrin is metabolised to maltose and maltotriose. A GDH-PQQ glucometer will falsely overestimate the blood glucose → the patient (or staff) may give insulin for a falsely high reading → fatal hypoglycaemia.
- Patients receiving intravenous immunoglobulin (IVIG) formulated with maltose face the same risk.
Critical Safety Point – GDH-PQQ and Icodextrin
Never use a GDH-PQQ or glucose-dye-oxidoreductase system that is susceptible to maltose in a patient using icodextrin. Check the exact meter/strip label for any maltose-containing drug or biologic. Use a validated glucose-specific system; do not infer safety from an enzyme acronym alone. [8]
The lecture's “2.5–28 mmol/L” range is an illustrative legacy range, not a universal specification. Current devices have model-specific reportable ranges and performance claims.
Why? Slide 27 plots proficiency-testing performance: central-laboratory glucose CVs cluster around roughly 1–3%, whereas many POCT systems are around 3–7% with conspicuous outliers above 10%. The figure supports the direction of the comparison, not a single universal CV. Accuracy can worsen near reportable limits and with shock/poor peripheral perfusion, oedema, haematocrit extremes, contaminated fingers, wrong strip storage or interfering medicines. [9]
The slide says to “always send a concomitant fluoride-oxalate” sample. That is a useful warning against over-trusting a low bedside value, but not a universal current rule for every routine meter check.
Repeat a surprising result immediately after checking patient ID, sample quality, strip/lot/expiry and technique. Obtain a promptly processed venous plasma glucose using the local laboratory's accepted tube and handling protocol when the repeat remains inconsistent with the patient, is at/outside the device range, or a definitive value will change high-risk treatment. Sodium fluoride inhibits enolase only after an initial delay, so “fluoride tube” does not replace prompt processing. ADA 2026 likewise recommends laboratory confirmation for a repeated POCT result that does not fit the clinical state. [9]
"Take concomitant blood samples for Insulin, C-Peptide, Cortisol, GH, etc., if hypoglycaemia is clinically evident; but don't delay any clinical interventions to await the results – treat the hypoglycaemia straightaway after the blood sampling." [1]
Clinical reasoning: If unexplained hypoglycaemia is strongly suspected, draw the appropriate critical sample before carbohydrate only when this can be done immediately and safely. Never delay treatment in an impaired, seizing or otherwise unstable patient. A low capillary value in shock should be treated on the clinical risk while a venous/plasma sample is obtained; waiting for confirmation must not postpone rescue glucose.
The slide mentions "Calibration" as a key point [1]
- Many current meters are factory-coded/no-code; older systems may use a strip code or calibration chip. Follow the exact device instructions rather than entering a code by habit.
- Whole blood vs. plasma calibration: Capillary blood glucometers measure whole blood glucose, but many are factory-calibrated to report plasma-equivalent values (roughly 11% higher than whole blood). This can cause confusion if compared directly to a central lab plasma glucose.
From the interferences lecture [3], additional factors affecting glucometer accuracy include:
- Haematocrit: Values outside the meter's validated range can bias a result; the direction and magnitude depend on the strip technology, so use the device interference table rather than memorising a universal arrow.
- Peripheral hypoperfusion/shock: Capillary blood does not reflect arterial glucose.
- Altitude, temperature, humidity: affect electrochemical reactions on test strips.
From the lecture slide [1]:
Specimen Handling Rules
| Rule | Rationale |
|---|---|
| Choose the right specimen | Arterial blood is required when accurate oxygenation assessment is needed; a venous gas can answer selected acid–base questions but venous pO₂ must not be used as arterial oxygenation |
| Expel air and cap promptly | Air drives pO₂ toward ambient, usually lowers pCO₂, and the size/direction of the pO₂ error depend on the starting sample and exposure time |
| Positive patient identification | Use the institution's approved label at the bedside; “GUM label” is local historical wording, not a universal specimen standard |
| Mix gently and analyse immediately | Balanced dry heparin must be distributed and clots avoided; delay permits cellular O₂ consumption and CO₂/lactate production |
| Do not rely on the slide's 90-minute rule | For a modern plastic syringe, CLSI-derived guidance is room-temperature analysis within about 30 minutes (about 15 minutes when pO₂ is critical); routine icing/refrigeration of plastic syringes can itself alter gases. Follow the validated local/device protocol. [10] |
The cartridge drawing on slide 28 shows the sample well feeding a sealed channel containing sensors and electrical contact pads; the handheld reader converts the sensor signals while a downloader/connectivity system transfers the result. This is why correct fill volume, bubble-free loading, cartridge storage and electronic traceability are part of analytical quality—not merely “operator convenience.”
Pre-analytical Errors – The Biggest Threat to ABG Accuracy
Most errors in blood gas results are pre-analytical: air bubbles, delayed analysis, wrong patient label, venous instead of arterial, insufficient sample volume, and clotted specimens. These are all avoidable with proper training – which is why the lecture emphasises SOP, training, and certification.
10. Other POCT Applications (Brief Notes)
- A validated troponin POCT assay can shorten chest-pain pathways when it meets the institution's analytical and timing requirements.
- Do not apply a high-sensitivity troponin algorithm to a device that is not validated as a high-sensitivity assay; use assay-specific cut-offs and serial intervals.
- Activated Clotting Time (ACT): used in cardiac catheterisation lab and cardiac surgery to monitor heparin effect.
- Thromboelastography (TEG) / ROTEM: used in massive transfusion protocols, liver transplant, obstetric haemorrhage.
- Enables same-visit DM management in primary care.
- Use a method with appropriate certification/traceability. Diabetes diagnosis is based on standard A1c or plasma-glucose criteria and generally requires confirmation unless unequivocal hyperglycaemia is present; not every clinic device is authorised for diagnosis. [14]
- Guaiac-based (older) vs. faecal immunochemical test (FIT, newer and more specific for lower GI bleeding).
- 4th generation: detects both HIV-1/2 antibodies and p24 antigen.
- Reduces window period compared to antibody-only tests.
- A reactive screen is followed by an HIV-1/HIV-2 antibody differentiation assay; if that is negative or indeterminate, perform diagnostic HIV-1 NAT. Western blot is historical and no longer the routine supplemental step in the current CDC/APHL algorithm. [12]
| Feature | POCT | Central Lab |
|---|---|---|
| TAT | Minutes | Hours (may be 30 min to several hours) |
| Sample volume | Very small (capillary) | Larger (venous) |
| Operator | Nurse, doctor, patient | Laboratory scientist |
| Accuracy | Device-, matrix- and context-dependent; may be adequate for its intended decision but vulnerable to identifiable interferences | Higher analytical precision for most measurands; still subject to pre-analytical and method error |
| Precision (CV%) | Higher CV (less precise) | Lower CV (more precise) |
| Menu | Limited (single analyte or small panel) | Comprehensive |
| QC/QA | Required but often less rigorously implemented | Stringent, continuous |
| Cost per test | Higher (reagent cartridges) | Lower (economies of scale) |
| Connectivity | May not auto-upload to EMR | Fully integrated with LIS/EMR |
| Best suited for | Time-critical decisions, remote settings | Definitive diagnosis, monitoring, complex panels |
| Topic | Relevant GC/CFB Lecture | Connection |
|---|---|---|
| Laboratory test interpretation | CFB MED10 (Use of Laboratory Test) [2] | POCT as one modality; understanding sensitivity/specificity applies equally |
| Interferences | Chemical Pathology Seminar on Interferences [3] | Haematocrit, drugs, oxygen tension affecting glucometers |
| DKA monitoring | GC 157 (Paediatric Chemical Pathology) | β-OHB meters superior to urine ketone dipstick |
| Infection diagnosis | GC 101 (Diagnosis of Infections) | RADT, rapid lateral-flow assays for HIV, COVID-19, TB urine LAM |
| Pregnancy | CFB OGPAE01-1 | Urine/serum hCG in early pregnancy |
| Pharmacogenomics | Intro to Clinical Pharmacology (I) [6] | VerifyNow assay (POCT for platelet function) to detect clopidogrel resistance |
Exam Intelligence
| Trap | How to Avoid |
|---|---|
| "Urine dipstick ketones are negative, so no DKA" | Remember dipstick misses β-OHB, the predominant ketone in DKA |
| "Negative urine pregnancy test excludes pregnancy" | No – can be falsely negative due to dilute urine, early pregnancy, variant-specific antibodies |
| "Glucometer reading of 2.5 mmol/L must be exact" | Check technique and repeat; if still discordant/extreme, obtain a promptly processed venous plasma glucose without delaying rescue treatment |
| "GDH-PQQ glucometer is interchangeable with GOx" | Susceptible GDH-PQQ systems detect maltose formed from icodextrin → dangerous in PD patients |
| "POCT doesn't need QC because it's just bedside" | POCT requires IQC and EQA just like central lab |
| "A faint line on pregnancy test = negative" | A faint test line within the read window, with a valid control, is positive |
| "Wait for lab confirmation before treating hypoglycaemia" | If a critical sample can be drawn immediately, take it; never delay rescue treatment |
- UPT format: pregnancy devices are sandwich assays (test line present = positive); drug screens are usually competitive (test line absent = presumptive positive). Both require a control line.
- Glucose confirmation: the key is a promptly processed venous plasma sample using the local laboratory pathway; fluoride does not instantly stop glycolysis.
- GDH-PQQ vs GOx: susceptible GDH-PQQ systems react with maltose/other sugars; icodextrin causes danger through maltose metabolites. GOx is glucose-selective but some designs are oxygen-dependent.
- Blood gases: air moves pO₂ toward ambient and lowers pCO₂; modern plastic syringes should generally be analysed at room temperature within 30 minutes, sooner when pO₂ is critical—not routinely refrigerated for 90 minutes.
High Yield Summary
-
POCT
- = Any test at bedside enabling immediate clinical action → key benefit is reduced TAT but ONLY if results are accurate and reliable.
-
Governance
- SOP, competency, IQC/EQA, patient/operator/device/lot traceability, documentation, maintenance, connectivity and safety are mandatory. The slide's ISO 22870:2006 is historical; POCT is now covered within ISO 15189:2022.
-
Urine dipstick ketones
- Nitroprusside method detects acetoacetate/acetone but NOT β-OHB (the predominant ketone in DKA) → use blood β-OHB meter for DKA monitoring.
-
Urine pregnancy test
- Threshold varies by kit; different antibody pairs detect hCG variants differently. Early/dilute urine and rare hook/hook-like effects mean negative does not exclude pregnancy. A clinic–result mismatch requires quantitative serum hCG plus the appropriate ultrasound pathway.
-
Glucometer
- Susceptible GDH-PQQ devices misread maltose from icodextrin or some drug formulations as glucose. Reportable range and interferences are device-specific. Repeat/confirm unexpected or extreme readings, but never delay hypoglycaemia treatment; obtain a critical sample first only if immediately safe.
-
ABG POCT
- Use arterial blood when oxygenation is required, expel air, mix heparin, label correctly and analyse promptly. The slide's routine refrigeration/90-minute rule is obsolete for modern plastic syringes; follow the validated local protocol (usually ≤30 minutes at room temperature, sooner for pO₂).
-
Drug of abuse POCT
- Competitive immunoassay: with a valid control, absence of the drug test line is a presumptive positive. Confirm when the result is disputed or carries high clinical/legal consequence.
Active Recall - POCT Lecture Notes
[1] Lecture slides: GC 158. Point-of-care testing (POCT).pdf [2] Lecture slides: CFB (MED10) The use of laboratory test in clinical medicine.pdf (p.45-46) [3] Lecture slides: Chemical Pathology Seminar_Interferences in laboratory testing 20240912.pdf [4] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p.131) [5] Senior notes: Ryan Ho Respiratory.pdf (p.51) [6] Senior notes: Introduction to Clinical pharmacology (I) (Pharmaco- Genomics, Precision Medicine).pdf (p.3) [7] ISO 22870:2016 catalogue entry — withdrawn and revised by ISO 15189:2022 [8] FDA-approved Extraneal labelling: glucose-specific testing and GDH-PQQ/glucose-dye-oxidoreductase warning [9] ADA Standards of Care in Diabetes—2026: diabetes care in hospital, POCT glucose limitations and confirmation [10] Preanalytical considerations in blood gas analysis (CLSI/IFCC synthesis) [11] FDA: drugs-of-abuse home/rapid tests provide preliminary or presumptive results [12] CDC HIV diagnostic algorithm: antibody differentiation followed by NAT for discordant results [13] Griffey et al. Hook-like effect in false-negative urine hCG POCT, J Emerg Med 2013 [14] ADA Standards of Care in Diabetes—2026: diagnosis and classification
GC157 Paediatric Chemical Pathology
Paediatric chemical pathology is the subspecialty of clinical biochemistry focused on the diagnosis and monitoring of metabolic, endocrine, and biochemical disorders in neonates, infants, and children.
GC159 Research Ethics (notes)
Research ethics is the framework of principles and regulatory guidelines—including informed consent, beneficence, non-maleficence, justice, and institutional review—that govern the conduct of biomedical and clinical research involving human subjects.