This test measures the concentration of dissolved particles (osmolality) in your blood. This test can help diagnose a fluid or electrolyte imbalance including dehydration. Electrolytes are mineral salts that help move nutrients into your cells and waste products out of your cells. Electrolytes also control your acidity and pH levels. The more diluted your blood and urine are the lower the concentration of particles. When there is less water in your blood the concentration of particles is greater. Osmolality increases when you are dehydrated and decreases when you have too much fluid in your blood.