Do Nutrient Blood Tests Even Work?

so blood tests are routinely taken to assess whether a person is deficient in certain nutrients from their diets. But do these even work? I mean, if it's found that someone has low blood iron isn't that just based on their most recent meal? A person could be deficient in their tissues and organs of a nutrient like iron, but if they had an iron rich meal before the blood tests were taken then this deficiency would not show up.

My point is that blood tests are fairly useless because they only show what is currently circulating in the blood at any given time and this is largely precipitated by nothing more than the nutrient content of their most recent meal.

 

... good observations there, flutterby!