A Prealbumin blood test measures prealbumin levels in your blood. Prealbumin is a protein synthesized in your liver. It helps carry thyroid hormones and vitamin A through your bloodstream as well as regulate energy consumption in the body. If your prealbumin levels are lower than normal, it may be a sign of malnutrition, a condition which your body lacks the calories, vitamins, and/or minerals needed to support normal functions.