Water and Electrolyte Balance Part 4 Flashcards
Urine osmolality
- principle clinical use of its measurement
assess renal concentrating and diluting ability
Urine osmolality
- reference range
300-1000 mOsm/kg
Urine osmolality
- Three specific conditions in which it is decreased
- Diabetes insipidus
- Polydipsia
- Renal failure
Urine osmolality
- One specific condition in which it is increased
Syndrome of Inappropriate ADH Secretion (SIADH)
Calculation for serum osmolality
1.86 (Na+) + BUN/2.8 + Glucose/18
Calculation for osmolal gap
Measured serum osmolality minus calculated serum osmolality
three methods by which sodium and potassium may be quantitated
- atomic absorption spectroscopy (reference method)
- flame photometry (old method)
3 ionselective electodes (most common)
Chloride Method Principle: Chloride is able to displace thiocyanate from mercuric thiocyanate. The reacts with ferric iron to form a red complex
colorimetric (mercuric thiocyanate and ferric nitrate)
Chloride Method Principle: titration that is the reference method for chloride
Coulometric/ amperometric
Chloride Method Principle: Most common today; uses a silver/silver chloride reference electrode
Ion-selective electrode
Chloride Method Principle: Based on determination of chloride-dependent alpha-amylase activity
Enzymatic (chloride method)
*Chloride Method Principle: Pilocarpine iontophoresis
Sweat chloride (iontophoresis)
Purposes of the reagents in the sweat chloride test
*
What is the historical calcium precipitation method and two specific dyes used in the spectrophotometric method for measuring calcium
Historical method: was precipitation with oxalate (Clark and Collip method)
Spectrophotometric: o-cresolphthalein or arsenazo III
Three reagents used in photometric magnesium methods
CalMAGite, formazan, methylthymol blue
Reagent used in the most common phosphorus method
*Photometric method: reaction of phosphate ions with ammonium molybdate, measured by UV absorption or reduction to the colored compound molybdenum blue
Specimen and anticoagulant interferences for sodium method
- Can analyze serum, plasma, whole blood, urine, or other
- No Na in anticoagulant
- separate serum/plasma from cells within 3 hours
Specimen and anticoagulant interferences for potassium method
- Can analyze serum, plasma, whole blood, urine, or other
- No K salt in anticoagulant
- No hemolysis for K
- separate serum/plasma from cells within 3 hours to prevent K leakage
Specimen and anticoagulant interferences for chloride method
- Serum or heparinized plasma
* *2. sweat chloride by pilocarpine iontophoresis
Specimen and anticoagulant interferences for bicarbonate/total carbon dioxide method
- Serum, heparinized plasma, or whole blood (usually blood gas specimen)
- Handled anaerobically b/c loss of CO2
Specimen and anticoagulant interferences for magnesium method
- Serum or heparinized plasma
2. NO HEMOLYSIS
Specimen and anticoagulant interferences for calcium method
- Serum or heparinized plasma
- Promptly separate from cells to prevent uptake of Ca2+ by RBCs
- CANNOT use anticoagulants such as EDTA, oxalate, or fluoride that chelate or precipitate calcium
Specimen and anticoagulant interferences for phosphorus method
- Serum or heparinized plasma
- No EDTA or citrate or oxalate anticoagulants as they interfere with formation of phosphomolybdate complex
- NO HEMOLYSIS
- Separate from cells promptly
Electrolytes for which a hemolyzed specimen is unacceptable
NO HEMOLYSIS:
- K+
- Magnesium
- Phosphorus
