Point of Care Testing

Whether it's an ABG machine in ED, a CRP testing machine in a GP surgery, or an iSTAT used in a community-based service (high-octane PHEM or high-impact admission-alternative community frailty/"Hospital At Home" schemes) or in the RATs area of the ED, Point of care testing (POCT) use is gaining ground in unscheduled care.

Now, in my opinion, POCT is fantastic - I am a fan. It seems to be engrained into British culture that "urgent blood tests" are part of the package that comes with "going into hospital". But shipping a patient off to hospital just because you need to know their U&E means they fall into the gravitational pull of the hospital's black hole; they and their family/carers expect an admission; and a drama quickly becomes a crisis that escalates into an avoidable admission. Being able to stop that bandwagon before it gathers pace using your "lab in a bag" to supplement your clinical assessment within minutes, rather than hours ("Your GP referred your mum to us as s/he wanted to make sure your mum weren't dangerously dehydrated - she isn't, there's no need to go to hospital, instead we'll do...") is near-miraculous.

But have you ever stopped for a moment to learn how to use the POCT you have access to ... or have you only learned how to process a sample in the machine(s) you use?

This is important stuff, but until - on secondment - I started to talk to our clinical biochemists more regularly, I was largely oblivious (either unknown unknowns, or stuff long-forgotten) to some of the crucial information included on this infographic created in partnership with our Principal Clinical Biochemist Sharman Harris. (If clicking on that link or the photo doesn't work, you can download the full-resolution PDF from the Downloads page)

For example:

• I had no idea that the haemoglobin result on most ABG samples is typically calculated, not measured.

• I didn't know that very high bilirubin can interfere with formal laboratory measurement of creatinine (using the JAFFE method).

• And if I'm being honest, I have never remembered to correct a sodium result in a patient with hyperglycaemia unless their sodium results were below the reference range.

But there's another aspect to using POCT... not the measurement and technical aspects, but psychological aspects for the clinician. Just as a near-instant results can disarm a family gearing up to admit granny, it can also disarm your diagnostic and clinical thought-process. When there's a 90-120 minute (or next day, as in GP) turnaround to getting your lab results, your little grey cells will have pondered over the patient, even if you never realised they were. Getting a result so quickly will deprive you of that thinking time. Be aware of this!

Sharman and I are up for creating a "Point Of Care testing II" if our infographic here inspires the #Medtwitter hive mind comes up with a batch of other crucial snippets - please do participate using the hashtag #POCT.

Update history

• Downloadable PDF updated to v1.1 at 19.50 on 29/11/2019 to re-word the creatinine information on Enzymatic methods.