MLAB 2401: Clinical Chemistry Keri Brophy-Martinez Methods of Measurement: Mineral and Bone Metabolism Determination of Total Calcium Colorimetric ◦ O-cresolphthalein Calcium in alkaline solution reacts with ocresolphthalein complexone to form a purple complex Proportional to the calcium concentration Uses 8-quinolinol or 8-hydroxyquioline to remove Mg ions ◦ Arsenzo III dye Atomic Absorption Spectrophotometry ◦ Reference method Specimen Requirements: Calcium( total) Serum Lithium heparin plasma Avoid the use of anticoagulants with EDTA or oxalate Determination of Free Calcium Ion selective electrodes used pH dependent Selectively and reversibly bind calcium ions As calcium binds to the membrane a potential develops which is proportional to the concentration Specimen Requirements: Calcium (Ionized) Samples must be collected anaerobically Heparinized whole blood preferred Plasma Serum Reference Ranges • Calcium, total 8.60-10.0 mg/dL • Ionized Calcium 4.60-5.08 mg/dL Determination of Phosphorus Formation of ammonium phosphomolybdate complex Complex measured by UV absorption at 340 nm or reduced to molybdenum blue and read between 600-700 nm Specimen Requirements: Phosphorus Serum Lithium heparin plasma Avoid hemolysis and certain anticoagulants Diural variation a factor Reference Range: Phosphorus 2.5-4.5 mg/dL Determination of Magnesium Colorimetric ◦ Calmagite Mg2+ binds with calmagite to for a reddish-violet complex, read at 532 nm ◦ Formazen dye Mg2+ binds with the dye to form a colored product read at 660 nm ◦ Methylthymol blue Mg2+ binds with the chromogen to form a colored complex Atomic Absorption Spectrophotometry ◦ Reference method Specimen Requirements: Magnesium Serum Heparinized plasma Avoid hemolysis Remove serum from cells ASAP Reference Range: Magnesium 1.6-2.6 mg/dL References Bishop, M., Fody, E., & Schoeff, l. (2010). Clinical Chemistry: Techniques, principles, Correlations. Baltimore: Wolters Kluwer Lippincott Williams & Wilkins. Sunheimer, R., & Graves, L. (2010). Clinical Laboratory Chemistry. Upper Saddle River: Pearson .