Point of Care Testing
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Direct answer
A glucometer reading is only as good as the strip chemistry, the operator's technique and the quality control behind it — which is the whole governance problem of point-of-care testing: diagnostic assays performed outside the laboratory, at or near the patient, by non-laboratory staff. The devices are genuinely powerful: glucose oxidase or glucose dehydrogenase strips with amperometric readout give results in seconds from a finger-prick; urine pregnancy and dengue and malaria rapid cards, blood gas analysers, INR coagulometers and handheld haemoglobinometers bring the laboratory to the bedside and the camp. But each device imports laboratory obligations — training and certification of operators, two-level quality control at defined intervals, calibration verification, results comparable to the central laboratory (the plasma-versus-whole-blood 10-12 per cent gap on glucose meters), and a record trail — because an unmanaged POCT programme simply relocates errors closer to the patient, where they are acted on faster.
What you must remember
- Glucometer chemistry: glucose oxidase (sensitive to oxygen tension and interfering reducing substances) or glucose dehydrogenase (PQQ variants affected by maltose, icodextrin dialysate — the classic false-high) — amperometric strips read whole blood, calibrated to plasma-equivalent values roughly 10-12 per cent higher.
- Clinical limitations: haematocrit extremes distort readings, as do paracetamol overdose levels on some strips, poor perfusion, and expired or mishandled strips (heat and humidity in Indian conditions shorten strip life once vials are opened).
- Quality control discipline: two-level liquid controls at the manufacturer's frequency (commonly daily per device per operator shift), immediate lockout on failure, and lot verification whenever a new strip lot opens.
- Comparability exercises: periodic parallel testing of POCT results against the central laboratory method, with acceptable bias criteria, so ward and laboratory numbers tell one story.
- Governance under quality systems: a POCT committee or coordinator, device inventory, operator training and re-certification records, and NABL/ISO 15189 treatment of POCT as part of the laboratory's scope where results enter patient records.
- Programme uses: malaria and dengue rapid tests at peripheral facilities, glucometry at diabetes camps, urine pregnancy testing — POCT as the first rung of the public health laboratory ladder.
Governing a ward glucometer
An intensive care sister reports ward glucose readings disagreeing with the laboratory's by 60 mg/dL. Strip lot and expiry in date; both control levels in range — the device is not broken. The technique audit finds the cause: the finger was not dried after alcohol swabbing and the first drop was not wiped — pre-analytical technique, not chemistry, is the commonest POCT error. Re-training logged, comparison now acceptable.
The second scenario is the chemistry trap: a peritoneal dialysis patient on icodextrin shows glucometer readings above 400 mg/dL while clinically euglycaemic — the glucose dehydrogenase-PQQ strip mistakes icodextrin's maltose for glucose. Switch to a glucose-oxidase method or laboratory hexokinase and flag the chart: a textbook interference that has caused insulin overdoses.
The ownership question
Viva examiners ask who owns POCT: the answer under quality systems is the laboratory — or a committee it sits on — even though the devices live on wards, because results entering patient records demand method validation, training and audit regardless of location. The second question is what can go wrong at each layer: strip (expiry, storage, lot), device (calibration, battery, software), operator (technique, timing, transcription), and patient (haematocrit, interferents, perfusion) — asked as a four-layer list. The comparison question: why glucometer and laboratory values differ (whole blood versus plasma, capillary versus venous, method bias) and what gap is acceptable — commonly within 15 per cent, tighter in the critically ill. And the Indian programme angle — malaria and dengue rapid tests at sub-centre level feeding programme surveillance — earns the mark: POCT in India is the only testing some populations will ever reach.
Frequently asked questions
What is point of care testing and what are its advantages?
Laboratory testing performed at or near the patient by non-laboratory staff, giving rapid results that speed decisions — at the cost of governance obligations in training, quality control and comparability.
What interferences affect glucometer readings?
Haematocrit extremes, maltose or icodextrin (with glucose dehydrogenase-PQQ strips), high oxygen tension effects on glucose oxidase strips, wet fingers diluting samples, and expired or heat-damaged strips.
Why do glucometer and laboratory glucose values differ?
Meters read whole blood calibrated to plasma-equivalent values (roughly 10-12 per cent higher), capillary samples differ from venous, and method biases add discrepancies — acceptable difference criteria govern comparison.
How is quality control maintained for POCT devices?
Two-level controls at defined frequency (per device and operator), automatic lockout on failure, verification of each new strip lot, operator training and certification records, and periodic comparison against central laboratory methods.
Who is responsible for POCT quality under a laboratory quality system?
The laboratory or a POCT committee it anchors — owning device selection, method validation, operator training and audit — because POCT results enter patient records and must meet laboratory standards.