Some algorithms reference decisions based on a multiple of the upper limit of normal (ULN). This can be converted to a Z score.
Situation: elevated laboratory result
upper limit of normal =
= (mean) + ((multiplier) * (standard deviation))
where:
• The multiplier is often 2.5.
• If the mean and standard deviation for a test are not known, then they can be derived from the upper and lower limits of normal if results show a Gaussian distribution.
Z score =
= ((value) - (mean)) / (standard deviation)
To convert a multiple of the upper limit of normal to a Z score:
