Micronutrients are essential vitamins and minerals. Getting enough of them is important for good health. It’s rare in the United States to have medical conditions caused by lack of nutrients like vitamins A, B1, B12, C, D, and selenium. Most people get enough vitamins and minerals through their diet or over-the-counter vitamins. Blood samples are a proven way to measure the level of essential nutrients. Other tests have been created that look at nutrient levels inside cells. These tests are unproven. There are no published medical studies showing whether the cell tests are more accurate or useful than standard blood tests at measuring levels of vitamins or minerals. There are also no randomized controlled trials — studies that randomly put people in different study groups — exploring whether the cell tests are effective to screen for or diagnose nutrient deficiencies.