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I see many results in which potassium falls (a little) above the normal range. I was wondering at what level I should be concerned about sudden death being the presenting symptom.
I reflected that the context in which the result was found affects my decision making.
A routine test which identifies a raised value, is less alarming than a test which is done for a reason, such as the presence of s...
A routine test which identifies a raised value, is less alarming than a test which is done for a reason, such as the presence of symptoms or perhaps because of a medication change.
This is analagous to the significance of a symptom or sign in the context of a focussed query versus routine enquiry (or screening).
One way of looking at it is in terms of the test characteristics of a diagnostic test versus a screening test. A screening test may have a higher cut point to increase specificity and reduce false positives. A diagnostic test may have a lower cut point to increase sensitivity and reduce false negatives.
Alternatively, looking at it as a Bayesian probability calculation, when doing the test for a reason (eliciting a symptom or sign for a reason) the prior probability (of a problem) is greater and hence one is influenced more even if the test (or symptom/sign) has a relatively small positive LR.
This is a very roundabout way of saying that if in doing routine annual bloods on a patient with hypertension treated with an ACE, I discovered a K of 6 say, I would perhaps feel this was not a cause for urgency. Conversely if someone presented with weakness and palpitations having recently commenced an ACE for diabetic nephropathy I might judge the same value of K to be more serious.
On the basis of this I would be interested to know what type of patients were included in the prognostic studies identified. Were they a broad selection of the population, such as seen in primary care, or were they perhaps patients more at risk of hyperkalemia, and its consequences, such as patients with diabetic nephropathy? Similarly, what was the context in which ECGs were related to potassium levels?
1. de Palma J R, Glasziou P. The first symptom of hyperkalaemia is death. Evid Based Med 2004; 9: 134-135