Artefactual hyperkalemia - dangerous, expensive. And preventable.

Potassium is part of a renal profile, the most commonly ordered test in pathology. 
In N Devon we do just over 100000 primary care tests per year for a population of 160000
Assuming we are similar to others, that would be about 40 million primary care tests per year in the UK.

Most potassium in a blood sample sits inside the blood cells, and there is a large concentration gradient across the cell membranes. This is maintained through the the Na/K ATPase, which uses energy to drive sodium out of the cell, in return for potassium entering the cell. Because this is an enzymatic process it is extremely sensitive to environmental conditions. For instance, as temperature rises then the enzyme works faster, pumping more potassium out of the serum into the cell. Conversely, when it is cold the pump doesn't work well and potassium leaks out of the cells. All this means that the level of potassium in the serum can be affected by the conditions in which a non-stabilised sample is kept. When the ambient temperature is low, serum potassium will tend to rise.  We can see the effect of this when we look at the percentage of specimens from primary care with high and low potassiums throughout the year. 

In the winter (cold) the percentage of specimens with high potassiums rises markedly. 

Conversely the percentage of specimens with low potassiums rises in the summer months.
From this, we can work out the "true level" of high potassiums should be roughly between 1.5 and 2%. We can then estimate the number of spuriously raised potassiums across the year, and in N Devon this works out at about 8500. If this is replicated across the country, then that would be about 2 million spuriously raised potassiums across the UK from primary care every year.

Why does this matter? High potassium is potentially a life threatening medical emergency. It is very hard to manage these patients in the community.  With mildly elevated rises in potassium it is often appropriate to repeat the test. So at best, this generates unnecessary repeat work ("failure demand") with associated anxiety for patients. At worst, and particularly with higher levels of potassium, patients need to be admitted to hospital for assessment. We know from coding that this happens frequently (and this will be included in the GIRFT report). And this assumes that coding is accurate. We know that this may not always be the case and so may significantly underestimate the true scale of the problem. For instance, we have just reviewed a case of a patient who was admitted with an incidental finding of a potassium of 6.1 on routine bloods. Her creatinine at the time was 100.  By the time her bloods were repeated on the medical assessment unit her potassium was normal - but her creatinine was 122, and this generated an Acute Kidney Injury label. She was admitted - and the coded reason for admission was AKI. This shows how medicine has a tendency to generate its own problems - she was probably just dehydrated following the disruption to her daily pattern of life. 

For admitting hospitals this is clear unnecessary work and we can see how it even results in the occasional patient being admitted for overnight stays.  But for patients all of this this creates enormous amounts of anxiety and real logistical problems - we have just shot a video of a patient talking about how it feels to be told you have a potentially life threatening condition, and the consequences of having to try to arrange transport to hospital, with no idea how to look after your seriously ill parents at the same time. Or just thinking about who will look after the dog. Things that might not bother us in hospital, but can be catastrophic for citizens.

All of this is avoidable. A simple way to do this is to separate the blood cells and the serum, and this can be done easily be centrifugation of samples that are taken in serum-separating tubes (SST) - the standard gold tops used by most labs for biochemistry analysis. Usually this is done on receipt of the specimens in the lab, but it can be done at the point of collection. In North Devon we have provided all practices with centrifuges. A few practices now centrifuge all specimens. They have seen an almost complete removal of seasonal peaks and troughs of hyper- and hypo-kalaemia. 
There are other potential solutions that might deliver similar benefits, including things such as more timely transport, and temperature control. But we hope that the GIRFT process, by starting to shine a light on this problem, will encourage this avoidable problem to be taken more seriously by all pathology services.


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