Hyperkalaemia as an example of how clinician behaviour can be inferred from laboratory data

Abnormal results and repeat testing

There are three reasons that a potassium test might be high.

1.     It may be the tail of a “normal” population

2.     It may be an artefact

3.     It may come from a patient with a pathological reason for a high potassium

The first response to raised potassium is generally to repeat, as this helps distinguish results that are spuriously high. The urgency with which a test is repeated may depend on the level of the result, or on some other patient factors. Alternatively, clinicians may choose to live with the uncertainty of a result, and assume it is spuriously raised, or raised in a way that is not clinically important.

We have looked to see if tests done in primary care are repeated within 48 hours, and where this happens (Figure 2)

Figure 2 Location and frequency of repeat primary care potassium tests, according to initial result.

We can see that tests are slightly more likely to be repeated when potassium results rise above the reference range (>5.3), but that repeats are much more likely to occur when the result is 6.0 or above. This aligns with the level at which the laboratory telephones results. About 80% of these repeats are carried out in primary care. However, when the initial potassium result rises to 6.5 or higher, then the rate of retesting in the ED rises to over 50%.

Conclusion

This data supports the idea that we can think of high potassium results falling into three different categories, based on the resulting actions (Table 1).

Result category	Band	Clinician behaviour
Low high	5.4-5.9	May ignore, or repeat at a later date
Moderate high	6.0-6.4	More likely to repeat urgently
High high	>6.4	Very likely to repeat urgently, and more likely to admit to hospital

Table 1 Impact of potassium result in primary care on clinician behaviour

Figure 3 shows how these categories map onto the distribution of potassium results in primary care.

Figure 3 Distribution of potassium results in primary care 2012-2018