By law, lab reference values are determined by making 95% of the people who were analized in that lab fall withing the reference values. Only the highest and lowest 2.5% falloutside the reference values. Since most people analyzed were sick and their doctors suspected a problem in order to require the tests, this is obviously absurd and renders teh values pretty useless.

Most doctors do not know this and do not suspect that there is a probolem until the person falls outside the values.

In reality, when a person is quite healthy the range is quite narrow for most substances and when problems begin and are easier to correct the values begin to deviate from these narrow, optimal ranges in several substances the doctor can suspect certain conditions that can often be confirmed by additional tests and prevented at a fraction of the cost, time and risk than when they are detected in the advanced stage.

For example is Ca=10 and phosphorous=2.8 (which falls within the accepted reference range) one can suspect early hyperparathyroidsm which can be confirmed by analyzing parathyroid hormone, which is below 30 in most healthy people.
In most healthy people 8.75<Ca<9.3, so using these values to provide an idea of the deviation from optimal health provides a much better idea of the probability of disease than using reference values as wide as 8.2<Ca<10.5 or wider in some labs.

Similarly, many labs have a range in the order of 18<ferritin<250, 15<urea<45 and 2.9<uric acid<7 or wider, when in fact optimumal health results when 35<ferritin<58, 15<uric acid<21 and 3.4<uric acid<4.1 and higher levels greatly increase the risk of hypertension, insulin resistance (diabetes type II), cardiovascular and kidney disease, etc,