Potassium PDF - Biology

POTASSIUM Prepared by: Mike Lenard M. Leocadio, RMT Learning Objectives: Identify the major roles of potassium in the body Enumerate the different assays of potassium and the principle of each assay Know the clinical significance of potassium determination Introduction Potassium (K+)...

POTASSIUM Prepared by: Mike Lenard M. Leocadio, RMT Learning Objectives: Identify the major roles of potassium in the body Enumerate the different assays of potassium and the principle of each assay Know the clinical significance of potassium determination Introduction Potassium (K+) is the major intracellular cation in the body, with a concentration 20 times greater inside the cells than outside. Functions of K+ in the body include regulation of neuromuscular excitability, contraction of the heart, ICF volume, and H+ concentration Renal function related to tubular reabsorption and secre tion is important in the regulation of potassium balance. Initially, the proximal tubules reabsorb nearly all the K+ CLINICAL APPLICATIONS - below 3.5 mmol/L (hypokalemia) Hypokalemia - normal range (3.5 -5.1) Hypokalemia is a plasma K+ concentration below the lower limit of the reference range. Hypokalemia can occur with GI or urinary loss of K+ or with increased cellular uptake of K+. Symptoms (e.g., weakness, fatigue, and constipation) often become apparent as plasma K+ decreases below 3 mmol/L. Hypokalemia can lead to muscle weakness or paralysis, which can interfere with breathing.  - higher to 5.1mmol/L(hyperkalemia) Hyperkalemia - normal range (3.5 - 5.1) Patients with hyperkalemia often have an underlying disorder, such as renal insufficiency, diabetes mellitus, or metabolic acidosis, that contributes to hyperkalemia The most common cause of hyperkalemia in hospitalized patients is due to therapeutic K+ administration Determination of Potassium Specimen Serum, plasma, and urine may be acceptable for analysis. Hemolysis must be avoided because of the high K+ content of erythrocytes. Heparin is the anticoagulant of choice Urine specimens should be collected over a 24- hour period to eliminate the influence of diurnal variation Potassium - most sensitive analyte compare to other electrolytes Heparin - anticoagulant of choice when patient have thrombocytosis over >600,000 it interfere in K+ Test methodology As with Na+, the current method of choice is ISE. For ISE measurements, a valinomycin membrane is used to selectively bind K+, causing an impedance change that can be correlated to K+ concentration where KCl is the inner electrolyte solution Reference range in potassium is same in the reference range of sodium. K+ Flame emission color = violet/purple Test methodology LOCKHEAD AND PURCELL COLORIMETRIC METHOD CALCULATION OF RESULTS Source of Error If the patient's platelet count is elevated (thrombocytosis), serum K+ may be further elevated if a tourniquet is left on the arm too long during blood collection or if patients excessively clench their fists or otherwise exercise their forearms before venipuncture, cells may release K+ into the plasma storing blood on ice promotes the release of K+ from cells hemolysis occurs after the blood is drawn, K+ may be falsely elevated—the most common cause of artifactual hyperkalemia Pseudohyperkalemia - is the number one source of error; false increase of the K+. other source of error: - hemolysis - prolong of tourniquet - excessive clencing Room temperture - is need in K+ REFERENCE RANGE REFERENCE Clinical Chemistry: Principles, techniques, and Correlations, 8th ed. Michael L. Bishop, Edward P. Fody, and Larry Schoeff.