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In response to Robin Marks: Does anyone use an alternative to concentrated HCl in the bottle for 24 hour urine calcium collection ? Since the late 70's, we have used sulfamic acid (7 grams) in small, heat-sealed envelopes made of a water-soluble polymer. We prepare these ourselves. For reference re: use of sulfamic acid: Peterson JI, Young, DS, Clin. Chem. 1971; 17:954-5. Many of patients in the rural areas we serve take a urine jug home and return 6 weeks later; hence some precaution is required during transport and storage. We also had a prominent urologist have an accident with 6N HCl during a personal collection -additional motivation for finding innovative approaches. Envelopes from: Quicksol A (QSA) bags, 1.5 mil, 2-1/4 x 4 inches $30 /1000 Polymer Films, Inc 301 Heffernan Drive West Haven CT 06516 For combinations of uric acid, oxalate, citrate, and calcium, we have also used a combination powder: EDTA (di-K salt, 9 g) + thymol (1 g) to keep oxalates and Ca soluble while not precipitating urates. This requires measuring urinary Ca (or Mg) by atomic absorption. Also, since Mg is a cofactor for the citrate assay, we dilute urines with MgCl2 in the assay to ocvercome the effect of the EDTA. For use of EDTA, see: Chambers AH et.al., Clin Chem 1985; 31: 1703-5 Urivetzky, M et.al., J. Urology 1992; 147: 1215-8. Ron Haas, PhD Clinical Chemist Marshfield Clinic/St. Jos. Hosp. Marshfield, WI 715-387-7207 fax: 715-387-7121 [log in to unmask] %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%