Testing your baby after birth. A PKU test is done a day or two after your baby's birth. The test isn't done before the baby is 24 hours old or before the baby has ingested some protein in the diet to ensure accurate results.1  A nurse or lab technician collects a few drops of blood from your baby's heel or the bend in your baby's arm.ll 50 states in the United States require newborns to be screened for PKU. Many other countries also routinely screen infants for PKU. If you have PKU or a family history of it, your doctor may recommend screening tests before pregnancy or birth.
By Mayo Clinic Staff. Low potassium (hypokalemia) refers to a lower than normal potassium level in your bloodstream. Potassium is a chemical (electrolyte) that is critical to the proper functioning of nerve and muscles cells, particularly heart muscle cells. Normally, your blood potassium level is 3.6 to 5.2 millimoles per liter (mmol/L).
This is the most common cause of hypokalemia. Other causes of hypokalemia include: 1  Increased excretion (or loss) of potassium from your body. 2  Some medications may cause potassium loss which can lead to hypokalemia.3  Common medications include loop diuretics (such as Furosemide).ne way your body regulates blood potassium levels is by shifting potassium into and out of cells. When there is a breakdown or destruction of cells, the electrolyte potassium moves from inside of the cell to outside of the cell wall. This shift of potassium into the cells causes hypokalemia.