Sodium (SODIUM) PDF

SODIUM Prepared by: Mike Lenard M. Leocadio, RMT Learning Objectives: Identify the major roles of sodium in the body Enumerate the different assays of sodium and the principle of each assay Know the clinical significance of sodium determination Introduction Na+ is the most abundant c...

SODIUM Prepared by: Mike Lenard M. Leocadio, RMT Learning Objectives: Identify the major roles of sodium in the body Enumerate the different assays of sodium and the principle of each assay Know the clinical significance of sodium determination Introduction Na+ is the most abundant cation in the ECF, representing 90% of all extracellular cations, and largely determines the osmolality of the plasma. The plasma Na+ concentration depends greatly on the intake and excretion of water and, to a somewhat lesser degree, on the renal regulation of Na+ Normally, 60% to 75% of filtered Na+ is reabsorbed in the proximal tubule; electroneutrality is maintained by either Cl− reabsorption or hydrogen ion (H+) secretion. CLINICAL APPLICATIONS Hyponatremia Hyponatremia is defined as a serum/plasma level less than 135 mmol/L, and levels below 130 mmol/L are clinically significant. Hyponatremia is one of the most common electrolyte disorders in hospitalized and nonhospitalized patients and can be assessed either by the cause of the decrease or with the osmolality level. Hypernatremia Hypernatremia Hypernatremia (increased serum Na+ concentration) results from excess loss of water relative to Na+ loss, decreased water intake, or increased Na+ intake or retention. Hypernatremia is less commonly seen in hospitalized patients than hyponatremia Determination of Sodium Specimen Serum, plasma, and urine are all acceptable for Na+ measurements. When plasma is used, lithium heparin, ammonium heparin, and lithium oxalate are suitable anticoagulants. Hemolysis does not cause a significant change in serum or plasma values as a result of decreased levels of intracellular Na+. The specimen of choice in urine Na+ analyses is a 24-hour collection Test methodology Through the years, Na+ has been measured in various ways, including chemical methods, flame emission spectrophotometry, ISE’s and atomic absorption spectrophotometry (AAS). Chemical methods are outdated because of large sample volume requirements and lack of precision. ISE’s (ion selective electrode) are the most routinely used method in clinical laboratories Most analyzers use a glass ion-exchange membrane in its ISE system for Na+ measurement Test methodology The ISE method uses a semipermeable membrane to develop a potential produced by having different ion concentrations on either side of the membrane Test methodology There are two types of ISE measurement, based on sample preparation: direct and indirect. Direct measurement provides an undiluted sample to interact with the ISE membrane. With the indirect method, a diluted sample is used for measurement. There is no significant difference in results, except when samples are hyperlipidemic or hyperproteinemic. ALBANESE AND LEIN COLORIMETRIC METHOD CALCULATION OF RESULTS Source of Error One source of error with ISE’s is protein buildup on the membrane through continuous use. The protein-coated membranes cause poor selectivity, which results in poor reproducibility of results. REFERENCE RANGE REFERENCE Clinical Chemistry: Principles, techniques, and Correlations, 8th ed. Michael L. Bishop, Edward P. Fody, and Larry Schoeff.