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).
Signs and symptoms of hypokalemia include: 1  Weakness. 2  Fatigue. 3  Muscle cramps. 4  Constipation. 5  Problems with your heart's rhythm (arrhythmias)