Important Electrolytes Flashcards
Major extracellular cation
Sodium
Renal threshold for sodium
110-130 mmol/L (120 mmol/L)
Reference range for sodium
136–145 mmol/L (mEq/L)
Panic values for sodium
</= 120 mmol/L (hyponatremia), >/= 160 mmol/L (hypernatremia)
Most common method for sodium measurement
Ion-selective electrode (ISE) with glass silicate electrode
Difference between direct and indirect ISE
Direct measures undiluted, indirect measures diluted (prone to pseudohyponatremia)
Color observed in flame photometry for sodium
Yellow
Rarely used colorimetric method for sodium
Albanese-Lein (produces yellow color)
Causes of absolute sodium loss in hyponatremia
Addison’s disease, salt-losing nephropathy, ketonuria, prolonged vomiting or diarrhea, severe burns, diuretics
Cause of dilutional hyponatremia with water retention
Renal failure, CHF, nephrotic syndrome, hepatic cirrhosis
Condition causing water imbalance in hyponatremia
SIADH, increased water intake
Effect of SIADH on sodium and water
Increased ADH retention, relative water excess, pseudohyponatremia
Causes of high plasma osmolality in hyponatremia
Hyperglycemia, mannitol infusion
Causes of hypernatremia with absolute sodium increase
NaHCO3 excess, hyperaldosteronism (Conn’s syndrome)
Urine osmolality < 300 mOsm/kg in hypernatremia
Diabetes insipidus (low urine SG and Osm)
Urine osmolality 300–700 mOsm/kg in hypernatremia
Partial AVP defect, osmotic diuresis
Urine osmolality > 700 mOsm/kg in hypernatremia
Loss of thirst, insensible water loss, GI fluid loss, excess sodium intake
Direct ISE measures sodium in
Undiluted samples
Indirect ISE measures sodium in
Diluted samples (prone to pseudohyponatremia)
Causes of absolute sodium loss in hyponatremia
Addison’s disease, salt-losing nephropathy, ketonuria (DKA), prolonged vomiting or diarrhea, severe burns, diuretics
Pathophysiology of sodium loss in Addison’s disease
Primary adrenalism; decreased aldosterone leads to reduced sodium retention and increased potassium
Causes of dilutional hyponatremia due to water retention
Renal failure, CHF, nephrotic syndrome, hepatic cirrhosis
Causes of dilutional hyponatremia due to water imbalance
Increased water intake, SIADH
Mechanism of SIADH in hyponatremia
Increased ADH retention caused by tumors; hydrostatic pressure exceeds osmotic pressure, leading to pseudohyponatremia
Potassium concentration in cells compared to extracellular fluid
20x higher intracellularly; major intracellular cation
Reference range for potassium in serum
3.5–5.1 mmol/L
Reference range for potassium in plasma
3.5–4.5 mmol/L
Potassium level due to platelet release after clotting
5.1 mmol/L
Panic values for potassium
≤2.8 mmol/L (hypokalemia); ≥6.2 mmol/L (hyperkalemia)
Most common method for potassium measurement
ISE using valinomycin
Flame photometry flame color for potassium
Violet
Lockhead-Purcell method result for potassium
Color/Spectrophotometry = blue
Primary cause of hypokalemia in cellular shifts
Influx due to increased pH (alkalosis), insulin overdose
Mechanism of potassium influx in alkalosis
Increased pH causes hydrogen ion movement out of cells, driving potassium into cells
Effect of insulin overdose on potassium levels
Promotes cellular uptake of potassium, leading to hypokalemia
Effect of alkalosis on potassium distribution
Potassium increases inside RBCs (cellular influx)
Causes of hypokalemia due to GI loss
Vomiting, diarrhea, gastric suction, laxatives, malabsorption
Causes of hypokalemia due to renal loss
Renal tubular acidosis, hyperaldosteronism (↑ Na reabsorption, ↓ K excretion), thiazide diuretics
Hyperkalemia mechanism: cellular shift
Potassium moves outside cells (efflux) during acidosis, chemotherapy, muscle injury, leukemia, or hemolysis
Hyperkalemia mechanism: increased intake
Oral or IV potassium replacement
Hyperkalemia mechanism: decreased renal excretion
Renal failure, hypoaldosteronism, K-sparing diuretics
Causes of pseudohyperkalemia
Sample hemolysis, hemoconcentration/venous stasis, thrombocytosis, use of EDTA anticoagulant
Major extracellular anion
Chloride
Relationship with Sodium and HCO3-
Direct relationship with Sodium; inverse relationship with HCO3- (chloride shift)
Reference values for Serum (mEq/L)
98–107 mmol/L
Reference values for Sweat Chloride
<40 mmol/L
Panic values for Serum Chloride
≤80 mmol/L or ≥120 mmol/L
Panic values for Sweat Chloride
≥60 mmol/L (indicative of cystic fibrosis)
Method for sweat chloride analysis
Gibson and Cooke’s method (pilocarpine iontophoresis)
Common method for Chloride measurement
ISE with ion exchange membrane
Mercurimetric titration method for chloride
Schales-Schales method (blue-violet color with diphenylcarbazone)
Spectrophotometric chloride assay
Whitehorn titration (red complex with mercuric thiocyanate)
Hypochloremia causes
Same as sodium: aldosterone deficiency, salt-losing nephropathy, DKA, vomiting, diarrhea, severe burns, diuretics; metabolic alkalosis, compensated respiratory acidosis
Hyperchloremia causes
Same as sodium: renal tubular acidosis, GI loss of HCO3-, metabolic acidosis, compensated respiratory alkalosis
Inverse changes between Bicarbonate and Chloride
Increased bicarbonate = decreased chloride; decreased bicarbonate = increased chloride
Major extracellular anion
Chloride
Relationship with Sodium and HCO3-
Direct relationship with Sodium; inverse relationship with HCO3- (chloride shift)
Reference values for Serum (mEq/L)
98–107 mmol/L
Reference values for Sweat Chloride
<40 mmol/L
Panic values for Serum Chloride
≤80 mmol/L or ≥120 mmol/L
Panic values for Sweat Chloride
≥60 mmol/L (indicative of cystic fibrosis)
Method for sweat chloride analysis
Gibson and Cooke’s method (pilocarpine iontophoresis)
Common method for Chloride measurement
ISE with ion exchange membrane
Mercurimetric titration method for chloride
Schales-Schales method (blue-violet color with diphenylcarbazone)
Spectrophotometric chloride assay
Whitehorn titration (red complex with mercuric thiocyanate)
Hypochloremia causes
Same as sodium: aldosterone deficiency, salt-losing nephropathy, DKA, vomiting, diarrhea, severe burns, diuretics; metabolic alkalosis, compensated respiratory acidosis
Hyperchloremia causes
Same as sodium: renal tubular acidosis, GI loss of HCO3-, metabolic acidosis, compensated respiratory alkalosis
Inverse changes between Bicarbonate and Chloride
Increased bicarbonate = decreased chloride; decreased bicarbonate = increased chloride
Second major extracellular anion
Bicarbonate
Percentage of total CO2 at physiological pH
> 90% of the total CO2
Reference values for measured TCO2
23–27 mmol/L
Reference values for calculated HCO3–
22–26 mmol/L
Panic values for HCO3–
≤10 mmol/L or ≥40 mmol/L
Method for Total CO2 measurement
ISE (acidification of sample followed by electrode-based CO2 detection)
Enzymatic method for HCO3– measurement
Involves alkalinization to convert CO2 and H2CO3 to HCO3– followed by enzymatic reaction with PEP carboxylase and malate dehydrogenase (decreased absorbance at 340 nm)
Clinical significance of ↓ HCO3–
Metabolic acidosis, compensated respiratory alkalosis, RTA, GI loss of HCO3–
Clinical significance of ↑ HCO3–
Metabolic alkalosis, compensated respiratory acidosis
Cofactor of enzymes Magnesium
> 300 enzymes
Magnesium distribution
55% ionized, 30% bound to proteins, 15% bound to ions
Reference values for magnesium (mEq/L)
1.26–2.1 mEq/L
Reference values for magnesium (mg/dL)
1.51–2.52 mg/dL
Panic values of magnesium(mg/dL)
≤1 or ≥4.7 mg/dL
Reference method for magnesium
AAS (Atomic Absorption Spectrophotometry)
Dye-binding methods for magnesium
Calmagite (Red Violet), formazan, methylthymol blue, xylidyl blue
Dye-lake methods for magnesium
Titan yellow (ACD lake), Clayton yellow, thiazole yellow dye
Clinical significance of Hypomagnesemia
↓ intake (poor diet, starvation, chronic alcoholism), ↓ absorption (vomiting, diarrhea, malabsorption), ↑ excretion (renal, endocrine, drug-induced)
Clinical significance of Hypermagnesemia
↑ intake (antacids, enemas), ↓ excretion (renal failure, hypoaldosteronism)
Calcium - Plasma level regulation
PTH (Bone resorption, Vitamin D activation, Ca2+ reabsorption in kidneys), Active Vitamin D (intestinal calcium absorption), Calcitonin (inhibits PTH)
Calcium - Distribution
50% ionized, 40% bound to proteins (albumin), 10% bound to ions
Calcium - Reference values (total)
4.3-5 mEq/L (8.6-10 mg/dL)
Calcium - Panic values
≤6 mEq/L
Calcium - Methods (AAS)
Lanthanum oxide to chelate phosphates (PO4)
Calcium - Methods (ISE)
PVC membrane impregnated with calcium ion exchanger for ionized Ca measurement
Calcium - Methods (Dye-binding)
O-cresolphthalein complexone (CPC) method, Arsenazo III (violet color for Ca2+)
Calcium - Methods (Precipitation)
Clark-Collip oxalic acid precipitation, Ferro-Ham chloranilic acid precipitation
Calcium - Clinical significance (Hypocalcemia)
Primary hypoparathyroidism, secondary hyperparathyroidism, chronic renal failure, hypomagnesemia, ↓ albumin, pseudohypoparathyroidism, vitamin D deficiency, pancreatitis
Calcium - Clinical significance (Hypercalcemia)
Primary hyperparathyroidism, hypercalcemia of malignancy, multiple myeloma, vitamin D excess, prolonged immobilization
Phosphate - Classification
Major intracellular anion, component of essential biomolecules, measured as inorganic PO4
Phosphate - Reference range
2.4–4.4 mg/dL
Phosphate - Panic values
≤1 mg/dL; ≥8.9 mg/dL
Phosphate - Method (Fiske-Subbarow/Ammonium Molybdate)
PO4 + ammonium molybdate → Ammonium phosphomolybdate, UV: ↑ APM @ 340 nm, C/S: Phosphomolybdenum (Blue) A ↑ 600-700 nm
Phosphate - Clinical significance (Hypophosphatemia)
Diabetic ketoacidosis, long-term TPN, IBD, anorexia nervosa, alcoholism, hyperparathyroidism, vitamin D deficiency
Phosphate - Clinical significance (Hyperphosphatemia)
Renal failure, milk or laxatives, neoplastic disorders, intravascular hemolysis, lymphoblastic leukemia
Phosphate - Transcellular shifts
Intracellularly and extracellularly depending on where it is needed, influenced by bicarbonate
Phosphate - Regulation
Proximal Convoluted Tubule: reabsorption site, PTH: decreases reabsorption, Calcitonin: increases excretion, Vitamin D: increases absorption and reabsorption, Growth hormone: decreases renal excretion
Phosphate - Pre-Analytical Considerations
Avoid hemolysis, do not use Citrate, Oxalate, or EDTA plasma, circadian rhythm (low in evening, high in late morning)
Phosphate - Measurement/Analysis Methods
Ammonium phosphomolybdate (340 nm), Fiske and Subbarow (600 nm)
By-product of anaerobic glycolysis, indicates hypoxia
Lactate
Lactate - Reference values (venous blood)
Colorimetric (POD - complexed): 8.1-15.3 mg/dL; UV (enzymatic): 4.5-19.8 mg/dL
Lactate - Method (POD-coupled reaction)
Lactate + O2 → Lactate oxidase → pyruvate + H2O2 → H2O2 + chromogen (POD) → oxidized chromogen + H2O
Lactate - Method (Enzymatic-UV)
Lactate + NAD → Lactate dehydrogenase → pyruvate + NADH
Lactate - Type A Lactic Acidosis: Hypoxic/Ischemic
Shock, MI, severe CHF, pulmonary edema, severe blood loss
Lactate - Type B Lactic Acidosis Metabolic:
Diabetes mellitus, severe infection, leukemia, liver or renal disease, toxins (ethanol, methanol, salicylate poisoning)
Major extracellular cation
Sodium
Major intracellular cation
Potassium
Major extracellular anion
Chloride
Major intracellular anion
Phosphate