Please see comment from Lloyd in previous tracker item - 17392. We need a way to note that the test was done (completed), cancelled, or not performed. Currently the only values are:

D = completed
X = cancelled

We would like to add N - Not Performed

This will provide a cleaner implementation for situations where a result value was expected, but has not been provided because the test could not be performed. (contrast with 'completed' which implies that a value is present)