Most regret over a blood gas analyser arrives months after the purchase order, not on the day of the demonstration. The device looked affordable, the screen was clear, the sales visit went smoothly. Then the first delivery of cartridges lands with a price that quietly doubles your running cost. Or a clinician queries an oxygen saturation that was never measured at all, only estimated from a formula. By then the contract is signed and the budget is committed for years.
Knowing how to choose a blood gas analyser means asking the uncomfortable questions before money changes hands. These nine separate a device that fits your service from one that becomes a standing cost and a clinical risk.
1. Which parameters are measured, and which are calculated?
This is the trap that catches the most buyers. A blood gas analyser directly measures only a small set of values through its sensors: pH, the partial pressure of carbon dioxide (pCO2) and oxygen (pO2), and, where the right electrodes are fitted, electrolytes such as sodium, potassium and chloride, plus glucose and lactate. Much of the rest of the printout is derived by calculation.
Bicarbonate and base excess are computed from pH and pCO2. Oxygen saturation, unless the device carries co-oximetry, is estimated from pO2 using an assumed dissociation curve. Calculated values are useful, but they inherit the error of every input and the assumptions built into the equation. Ask the supplier for a plain list: which results come from a sensor, and which from a formula. A specification sheet that blurs the two is telling you something.
2. Do you need true co-oximetry?
Co-oximetry is the clearest reason the measured-versus-calculated question matters. True co-oximetry uses spectrophotometry to measure the actual haemoglobin fractions: total haemoglobin, oxyhaemoglobin, carboxyhaemoglobin (COHb) and methaemoglobin (MetHb). A device without it calculates saturation from pO2 and assumes haemoglobin is behaving normally.
That assumption fails in exactly the situations where you most need the truth. In carbon monoxide poisoning, a calculated saturation can read reassuringly high while measured oxyhaemoglobin is dangerously low. The same gap appears with methaemoglobinaemia. If your service sees smoke inhalation, suspected poisoning, paediatric emergencies or critical care, co-oximetry is a requirement, not an upgrade. A low-acuity clinic that never meets these presentations can reasonably forgo it and save the cost. Decide deliberately, rather than discovering the limitation during a resuscitation.
3. What does a single test actually cost?
The headline device price is the least useful number in the quotation. The figure that shapes your budget is the fully loaded cost per reportable result, and it has several parts:
- The cartridge, cassette or sensor consumable, priced per test or per pack.
- Calibration materials: solutions, gas bottles or onboard calibrant.
- Quality-control material at each level you are required to run.
- The service contract, including parts and call-out.
- Wastage from expired cartridges and failed runs.
A cheap analyser with costly single-use cartridges often loses to a dearer device with affordable consumables once you multiply by annual volume. Build the sum over the whole contract term, typically four or five years, and ask for cartridge pricing in writing with the expiry dating you will actually receive. Short-dated stock that expires before you can use it is pure waste, and it is common.
4. How heavy is the quality-control workload?
Quality control is a recurring labour cost, not a one-off setup. Every device needs internal QC at defined intervals and participation in an external quality assessment scheme. The questions that reveal the real burden are practical ones. How many control levels must run, and how often? Is QC automatic from an onboard cartridge, or does a member of staff prepare and run it by hand? How long does each cycle take, and does it lock the analyser while it runs?
A device that demands manual three-level QC every shift can absorb hours of staff time each week that never appeared in the business case. Onboard automatic QC reduces that labour but adds consumable cost, so the saving is in time rather than money. Either way, count it. For building a defensible routine, our guide to point-of-care quality control goes deeper than there is room for here.
5. Is the throughput matched to your real volume?
Analysers fall into rough classes. Handheld units running single-use cartridges suit low and intermittent volumes, a handful of tests a day. Benchtop cartridge or cassette systems handle moderate, steady demand. Large floor-standing analysers are built for the continuous load of an intensive care unit or a busy emergency department.
The expensive mistake runs in one direction more than the other: a low-volume clinic buying an ICU-class machine. A high-throughput analyser often calibrates itself on a fixed schedule and consumes reagent whether or not you test, so a device sized for hundreds of samples a day will burn money sitting idle in a clinic that runs ten. Match the class to your genuine peak and average demand, not to the busiest site in the sales reference list.
6. What is the calibration and maintenance burden?
Tied to throughput is how the device keeps itself in tune. Some analysers auto-calibrate at set intervals using onboard fluid or gas, which is convenient but consumes reagent continuously. Others calibrate per cartridge, so cost tracks use more closely. Ask what routine maintenance the operator must perform, how often sensors or modules need replacing, and what a sensor pack costs. A device that is cheap to buy and frequently down for maintenance is not cheap. Ask, too, whether the analyser needs a settling or warm-up period from cold, because that idle time matters in a service that does not run around the clock.
7. How much downtime should you expect, and what happens then?
Every analyser fails eventually, and in acute settings a dead blood gas machine is an immediate clinical problem. Ask for the realistic mean time between failures and the support model behind it. What is the call-out response time written into your contract? Is a loan or backup device provided while yours is repaired? If you run a single analyser, you are running a single point of failure, so weigh a second smaller unit or a documented fallback against the cost of being without results during a busy night.
8. What does the operator workflow demand?
The best analyser on paper can still fail in practice if the workflow does not suit your staff. Check the sample type and minimum volume, which matters for paediatric and difficult draws. Look at how the device handles a clotted or under-filled sample, how long training and competency assessment take, and whether operator lockout can stop untrained or unauthorised users from releasing results. In a department with high staff turnover, a device that is forgiving and quick to teach pays back every week.
9. How will results be captured and governed?
A measured result has no value until it reaches the record, correctly and traceably. If your team reads numbers off a screen and types them into a patient record, you have introduced a transcription error waiting to happen, and an audit trail with a gap in it. Look for an analyser that works with the devices and systems you already use, so results, operator identity and quality-control status sit in one governed view rather than living on the instrument.
This is where day-to-day oversight is won or lost: knowing which operators are in date, which controls have passed, and which results are still waiting to be signed off, across every device in the service. If governing results across your analysers is the part keeping you up at night, Talk to POCTIFY about support shaped around how your clinic actually runs.
How to choose a blood gas analyser with confidence
Score each candidate device against all nine as a side-by-side comparison, with extra weight on the measured-versus-calculated answer, the fully loaded cost per test, and the quality-control workload, because those three drive both safety and budget for years. The cheapest quotation rarely wins once the cartridges, the calibrant and the staff hours are counted, and the most capable machine is wasteful in a clinic that does not need it. The right answer is the device that fits your acuity, your volume and your team, and that you can govern with confidence once it is installed.
This article is for educational and operational guidance only and is not medical advice.
Frequently asked questions
What is the difference between measured and calculated parameters on a blood gas analyser?
pH, pCO2 and pO2 are measured directly by sensors, along with electrolytes, glucose and lactate where those electrodes are fitted. Bicarbonate, base excess and, without co-oximetry, oxygen saturation are calculated from those measurements. Calculated values carry the error of their inputs and the assumptions in the equation, so it matters which is which.
Do I need a co-oximeter in my blood gas analyser?
If your service may see carbon monoxide poisoning, methaemoglobinaemia, smoke inhalation, paediatric emergencies or critical care, then yes, because a calculated saturation can read normal when the patient is not. Lower-acuity clinics that never meet these cases can reasonably choose a device without true co-oximetry and save the cost.
How do I work out the true cost per test?
Add the consumable cartridge or cassette, calibration materials, quality-control material at every required level, the service contract, and wastage from expired or failed cartridges. Multiply by annual volume across the full contract term. A low device price paired with costly cartridges often ends up dearer than a higher price with affordable consumables.
Why does quality control count as a running cost?
QC consumes both consumable material and staff time at defined intervals, plus external quality assessment scheme fees. Manual multi-level QC every shift can take hours a week. Automatic onboard QC saves time but adds consumable cost. Either way it belongs in the business case rather than being treated as a one-off setup.
How do I match an analyser to my clinic’s volume?
Handheld single-use cartridge devices suit low, intermittent demand. Benchtop systems suit steady moderate volumes. Floor-standing analysers suit continuous high-volume critical care. A high-throughput device that auto-calibrates on a schedule wastes reagent when idle, so avoid buying ICU capacity for a low-volume clinic.
