Preanalytics: stable for 5 days at 2 - 8 °C, 1 month at -20°C, to avoid bacterial growth the pH must be <5 1 day prior to and during collecting the 24 hour urine sample, following foodstuffs should be avoided: coffee, tea, alcohol, nicotine. Following drugs can impact the test results: alpha-methyldopa, barbiturates, beta- receptor antagonists, chlorpromazine, clonidine, guanethidine, insulin, reserpine, salicylic acid, tranquilizers, sulfonamide, tetracyclines. With the consent of your doctor, you should stop taking the medication 7 days prior to starting the 24- hour urine collection.