The McAuley index is a handy surrogate measure of insulin resistance. It basically estimates rather than measures your likelihood of being insulin resistant.
It only needs 2 things, fasting insulin and fasting triglycerides . Such fasting indexes are usually not very useful because they have a high false-positive rate (i.e. it says you’re insulin resistant when in fact you’re not). However, the McAuley index is an exception to this rule. The problem with most fasting indexes is that they only capture a snapshot: the measurement in this very moment, which can be influenced by many factors, such as quality of sleep the night before or what you have eaten.
The reason why the McAuley index is more reliable is because it includes fasting triglycerides. Glucose and insulin levels don’t directly influence triglycerides, it is rather indirect and delayed in time. The fasting triglycerides value is, therefore, more stable over several hours, which makes it more reliable than standard fasting indexes. It is a shame that it is hardly known and under-used.