Urinary sodium and potassium
Gravity normalised urine samples were thawed prior to dilution to 1:100 with distilled water. Sodium and potassium concentrations were determined with a flame photometer (PFP-7, Jenway, UK). Standards of sodium (2–8 ppm) and potassium (5–40 ppm) were used to quantify levels prior to transforming into concentrations. Results are expressed in micromoles.