Electrolytes PDF

ELECTROLYTES mmol/kg) of solvent. - Charged ions found in intracellular fluid, related to several changes in the properties extracellular fluid, and of a solution, relative to pure interstitial fluid. water, su...

ELECTROLYTES mmol/kg) of solvent. - Charged ions found in intracellular fluid, related to several changes in the properties extracellular fluid, and of a solution, relative to pure interstitial fluid. water, such as freezing point depression and vapor pressure decrease. CATIONS SODIUM AKA NATRIUM - Are positively charged ions. The major cations in the body are sodium, - Major cations of extracellular fluid. potassium,calcium, and magnesium - Reference range: 136-145 mmol/L ANIONS - Changes in sodium results in changes in plasma volume - Are negatively charged ions. The major anions in the body are chloride, - Largest constituent of plasma osmolality bicarbonate, phosphate, sulfate, organic - Sodium is excreted in the urine when the acids, and proteins renal threshold Importance of Electrolytes for serum sodium exceeds 110-130 mmol/L 1. For volume and osmotic regulation. ( Na, K, Cl) Hormones Affecting Sodium Levels: 2. For myocardial rhythm and contractility. ( 1. Aldosterone K, Ca, Mg) - Promotes absorption of sodium in the 3. Important cofactors in enzyme activation. distal tubule. ( Ca, Mg, Zn, Cl, K ) - Promotes sodium retention and 4. For the regulation of adenosine potassium excretion. triphosphate (ATPase) ion pumps. (Mg) 2. Atrial Natriuretic Factor (ANF) 5. For neuromuscular excitability. ( K, Ca, - It blocks aldosterone and renin secretion Mg) and inhibits the action of 6. For the production and use of ATP from angiotensin II and vasopressin. glucose. ( Mg , PO4 ) - Causes natriuresis 7. Maintenance of acid-base balance. ( HCO3, K, Cl, PO4) Clinical significance: 8. Replication of DNA and the translation of mRNA. (Mg) 1. Hyponatremia occurs when serum sodium OSMOLALITY level is 5.0 mmol/L. POTASSIUM AKA KALIUM CHOLORIDE POTASSIUM Major anion of extracellular fluid - Major intracellular cation - Chief counter ion of sodium in ECF. - Reference range: 3.4-5.0 mmol/L - The only anion to serve as an enzyme - Because the concentration of potassium in activator (amylase). red blood cells is - Excreted in urine and sweat. higher than in serum, any level of hemolysis will falsely - Reference range: 98-107 mmol/L serum potassium results - Chloride levels change proportionally with sodium - Only 2% of the body’s total potassium circulates in plasma Clinical significance : Specimen considerations: 1. Hypochloremia occurs when serum chloride level is 107 increase in gross hemolysis) mmol/L b. Plasma levels are lower ( 0.1 - 0.7 mmol/L ) compare to serum levels Methods : because of the released of platelets into Bromide , cyanide and cysteine - serum on clot formation. interferences (chemical test and coulometric ) c. 10-20 % increase as a result if muscle activity. 1. Mercurimetric Titration ( Schales and Schales ) - 0.3-1.2 mmol/L increase = mild to moderate exercise Diphenylcarbazone = indicator - 2-3 mmol/L increase = vigorous exercise HgCl2 ( blue violet ) = end product ; fist clenching 2. Spectrophotometric methods d. Prolonged contact serum and red cell. a. Mercuric Thiocyanate ( Whitehorn e. Prolonged application of tourniquet. Titration Method ) Clinical significance: = red complex b. Ferric Perchlorate = colored complex 3. Coulometric Amperometric Titration - analytically when serum “electrolytes” are Cotlove Chloridometer ( cystic fibrosis ) quantified. The unmeasured cations include calcium and magnesium, whereas the 4. Ion Selective Electrode - ion exchange unmeasured anions include phosphate, membrane ( tri-n-octylpropylammonium sulfate, organic acids and proteins. chloride a. Two calculation methods commonly used: decanol) ; most commonly used method Na+ - ( Cl- + HCO3-) = anion gap BICARBONATE Expected anion gap: 7-16 mmol/L Second largest anion fraction of extracellular fluid (Na+ + K+) - (Cl- + HCO3-) = anion gap - Reference range: 22-29 mmol/L Expected anion gap: 10-20 mmolL - Clinically, the concentration of total carbon b. Increased anion gap can be caused by dioxide (ctCO2) is measured because it is uremia, lactic acidosis, ketoacidosis, difficult to measure HCO3. ctCO2 is hypernatremia and ingestion of methanol, comprised primarily of HCO3 along with ethylene glycol, or salicylate. It is also used smaller amounts of H2CO3 (carbonic acid), as an assessment of instrument errors. carbamino bound CO2, and dissolved C. Decreased anion gap can be caused by CO2.HCO3 accounts for approximately 90% hypoalbuminemia and hypercalcemia of measured ctCO2 CALCIUM - Bicarbonate is able to buffer excess H+, making bicarbonate an important buffer - Present almost exclusively in the plasma. system of blood. - Involved in blood coagulation, enzyme Clinical significance: activity, excitability of 1. Decreased ctCO2 associated with skeletal and cardiac muscle and maintenance metabolic of blood pressure. acidosis, diabetic ketoacidosis, salicylate - It is maximally absorbed in the duodenum. toxicity - Absorption is favored at an acidic pH. 2. Increased ctCO2 associated with - It is the free form of calcium that is metabolic biologically active. alkalosis, emphysema, severe vomiting - Decreased free (ionized) calcium levels Anion gap cause muscle spasms or untrolled muscle contractions called tetany. - This is a mathematical formula used to demonstrate electroneutrality of body fluids. Three forms of Calcium: It represents the difference between cations 1. Ionized (active) Calcium - 50% and anions that are not actually measured 2. Protein- bound Calcium - 40% 3. Complexed with Calcium - 10% increases tubular reabsorption of calcium in the kidneys - Ionized calcium is a sensitive and specific marker for calcium disorders. C. Calcitonin - For every 1 g/dL serum albumin decrease, 1. Released by the parafollicular cells of the there is 0.8 mg/Dl decrease in total Ca2+ thyroid gland when serum calcium levels hypocalcemia can be consequence of increases. reduced plasma albumin. 2. Inhibits vitamin D and parathyroid Regulation: hormone activity, thus decreasing serum calcium - Serum calcium is controlled by parathyroid hormone, vitamin D, and calcitonin 3. Medullary carcinoma of the thyroid gland is a neoplasm of the parafollicular cells, A. Parathyroid hormone (PTH) resulting in elevated serum levels of 1. A decreased in free (ionized) calcium calcitonin. stimulates the release of PTH by the parathyroid gland, and a rise in free calcium Clinical significance: terminates PTH release. A. Hypercalcemia is caused by primary 2. In bone, PTH activates osteoclasts to hyperparathyrodism, other endocrine break down bone with the release of disorders such as hypothyroidism and acute adrenal insufficiency, malignancy involving calcium bone, and renal failure. 3. In the kidneys, PTH increases tubular B. Hypocalcemia is caused by reabsorption of calcium and stimulates hypoparathyroidism, hypoalbuminemia, hydroxylation of vitamin D to the active chronic renal failure, magnesium deficiency, form and vitamin D deficiency. B. Vitamin D Causes of hypercalcemia : CHIMPS ( (cholecalciferol) 1. Obtained by diet or Cancer, hyperthyroidism, iatrogenic causes, exposure to sunlight multiple myeloma, hyperparathyroidism, and sarcoidosis. 2. Initially, vitamin D is transported to the liver, where it is hydroxylated but still Causes of hypocalcemia: CHARD ( calcitonin, hypoprathyroidism, alkalosis, inactive. Then the hydroxylated form is renal failure, vitamin D ) transported to the kidneys, where it is converted to Methods : 1,25-dihydroxycholecalciferol, the active 1. Precipitation and Redox titration form of the vitamin a. Clark Collip Precipitation- end product : 3. Calcium absorption in the intestine is Oxalic acid (purple color ) enhanced by vitamin D. In addition, PTH b. Ferro Ham Chloranilic Acid Precipitation - end product: Chloranilic acid (purple color ) include hemolysis, icterus, and lipemia; interferences for ion-specific electrode and 2. Ortho - Cresolphthalein Complexone change in blood pH in vitro before analysis Dyes (Colorimetric method ) d. Reference ranges Dye : arzeno III Total calcium (adults): 8.6-10.3 mg/dL Mg+ inhibitor : 8-hydroxyquinoline (chelator) Total calcium ( child ): 4.6-5.3 mg/Dl 3. EDTA Titration Method ( Bachra, Dawer PHOSPHORUS and Sobel ) Inorganic phosphorus 4. Ion Selective Electrode ( Liquid- - Inversely related to calcium membrane) - Maximally absorbed in the jejunum 5. Atomic Absorption Spectrophotometry - reference method (dissociation ) - Exists as organic phosphate or inorganic phosphate esters: 6. Emission Flame Photometry a. Organic phosphate - principal anion Methods, interferences, reference range within cells a. Methods used to measure total serum b. Inorganic phosphate - part of the blood calcium: Spectrophotometric (ortho- buffer cresolphthalein complexone, arsenazo III dye), ISE (ion-specific electrode), atomic Forms : absorption (reference method ) 1. Free -55% 1. Spectrophotometric methods use 2. Complexed with ions - 35% metallochromic indicators that bind calcium causing a color change. These methods are 3. Protein- bound - 10% easily automated. Factors affecting Phosphate 2. With ISE analysis, the specimen must be Concentration : acidified to convert protein-bound and complexed calcium to the free form in order 1. PTH- decreases phosphate by renal to measure total calcium. excretion B. Measure free (ionized) serum calcium: 2. Calcitonin - inhibits bone resorption Ion-specific electrode measures free form. 3. Growth hormone - increases phosphate Measurement is temperature sensitive, and renal absorption generally analysis is performed at 37C Practical considerations: C. Sources of error: Cannot use oxalate: citrate, or EDTA anticoagulants; 1. Fasting is required- a high CHO diet can interferences for spectrophotometric result to decrease levels. methods 2. Separate the serum from the red cells immediately after clotting is completed. Clinical significance: protein, 15% complexed. It is the free form of magnesium that is biologically active. a. Hyperphosphatemia is caused by renal failure, hypoparathyroidism, neoplastic Regulation diseases, lymphoblastic leukemia, and - The magnesium level is regulated by the intense exercise. kidneys through b. Hypophosphatemia is caused by diabetic reabsorption and excretion ketoacidosis, hyperparathyroidism, asthma, alcoholism, and malabsorption syndrome. - PTH enhances reabsorption by the kidneys and intestinal absorption Methods, interferences, reference range Factors affecting magnesium level in a. Ammonium molybdate + phosphate ions - blood: phosphomolybdate complex 1. Parathyroid Hormone (Colorless) read at 340 nm - Increased renal absorption of magnesium b. When aminoethanesulfonic acid is used to reduce the complex, a colored - Increased intestinal absorption of magnesium product is formed and read at 600-700 nm. +electrons Phosphomolybdenum —---- 2. Aldosterone and Thyroxine ----- molybdenum blue - Increased renal excretion of magnesium c. Sources of error: hemolysis, lipemia, icterus; cannot use oxalate, citrate, or Clinical significance EDTA anticoagulants a. Hypermagnesemia d. Reference range (adults) : 2.5-4.5 mg/Dl is caused by renal failure and excess Fiske Subbarow Method ( Ammonium antacids. molybdate method) b. Hypomagnesemia MAGNESIUM is caused by gastrointestinal disorders; renal - An intracellular cation second in diseases; hyperparathyroidism abundance to potassium (hypercalcemia); drugs (e.g. diuretic therapy, - Fourth most abundant cation in the body cardiac glycosides, cisplatin, cyclosporine ); diabetes mellitus with glycosuria; and - Majority is stored in bones; enzyme alcoholism due to dietary deficiency. activator. Methods, interferences, reference range - It is a vasodilator and cause decrease uterine hyperactivity in eclampsic states and a. Methods used to measure total serum magnesium: Calmagite, increase uterine blood flow - exists in plasma in three forms: 55%free methylthymol blue, atomic absorption (ionized), 30 % bound to spectrophotometry (reference method) b. Measure free (ionized) serum magnesium: Ion-selective electrodes c. Sources of error: hemolysis; cannot use oxalate, citrate or EDTA anticoagulants d. Reference range (adults) : 1.7-2.4 mg/Dl Methods 1. Colorimetric method a. Calmagite method = (+) reddish-violet complex b. Formazan dye method = (+)colored complex c. Magnesium Thymol Blue method = (+) colored complex 2. Atomic Absorption Spectrophotometry - reference method 3. Dye-lake method- Titan Yellow Dye ( Clayton Yellow or Thiazole Yellow )