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, but is always accompanied by the sodium assay. Changes in urine chloride levels usually reflect those of sodium except in the case of acid-base equilibrium disorder. The urine chloride level is expressed in millimoles per day (mmol/d) for 24-hour urine collection and millimoles per litre (mmol/L) for an isolated miction.
High levels of urine chloride may indicate dehydration, fasting, adrenal gland failure (Addison’s disease) or an increase in dietary intake of salt. A high urine level of both chloride and sodium indicates that an individual restricted to a low-salt diet is not complying with this diet. Lower urine chloride levels can be observed in overactive adrenal glands (Cushing syndrome, Conn’s syndrome), heart failure, malabsorption syndromes and diarrhea.