Measuring levels of chloride ions in urine is sometimes useful in investigating an abnormally high or low level of chloride in the blood. The urine chloride assay is never requested on its own; it is always accompanied by the sodium assay. Changes in urine chloride levels usually reflect changes in urine sodium levels, except in the case of acid-base equilibrium disorder. Urine chloride levels are expressed in millimoles per day (mmol/d) for a 24-hour urine collection and millimoles per litre (mmol/L) for an isolated urination.
High levels of urine chloride may indicate dehydration, fasting, adrenal gland failure (Addison’s disease) or increased dietary salt intake. A high urine level of both chloride and sodium indicates that a person restricted to a low-salt diet is not complying with this diet. Low urine chloride levels can be seen in overactive adrenal glands (Cushing’s syndrome, Conn’s syndrome), heart failure, malabsorption syndromes and diarrhea.