The Addy Count typically uses formaldehyde as a preservative. Eddy’s count is a quantitative test used to determine the presence of formed components in urine and generally requires a 12-hour urine collection for quantitative leukocyte counting. In order to avoid contamination of the specimen, in principle, urine samples should be refrigerated at 0 to 4°C as well as adding preservatives. Formaldehyde is the preservative commonly used in the Eddy’s count test. Since urine chemicals and formed components are unstable, physical and chemical changes begin to occur after they are excreted. Adding formaldehyde as a preservative can inhibit bacterial growth and immobilize cells, tubules, and other formed components in the urine to ensure the validity of the test results. It is important to add formaldehyde as a preservative in proportion to the hospital doctor’s instructions to ensure the reliability of the urine specimen and to avoid affecting the results.