Water and Electrolyte Balance Part 4

Question 1

Urine osmolality

- principle clinical use of its measurement

Answer 1

assess renal concentrating and diluting ability

Question 2

Urine osmolality

- reference range

Answer 2

300-1000 mOsm/kg

Question 3

Urine osmolality

- Three specific conditions in which it is decreased

Answer 3

1. Diabetes insipidus
2. Polydipsia
3. Renal failure

Question 4

Urine osmolality

- One specific condition in which it is increased

Answer 4

Syndrome of Inappropriate ADH Secretion (SIADH)

Question 5

Calculation for serum osmolality

Answer 5

1.86 (Na+) + BUN/2.8 + Glucose/18

Question 6

Calculation for osmolal gap

Answer 6

Measured serum osmolality minus calculated serum osmolality

Question 7

three methods by which sodium and potassium may be quantitated

Answer 7

1. atomic absorption spectroscopy (reference method)
2. flame photometry (old method)
   3 ionselective electodes (most common)

Question 8

Chloride Method Principle: Chloride is able to displace thiocyanate from mercuric thiocyanate. The reacts with ferric iron to form a red complex

Answer 8

colorimetric (mercuric thiocyanate and ferric nitrate)

Question 9

Chloride Method Principle: titration that is the reference method for chloride

Answer 9

Coulometric/ amperometric

Question 10

Chloride Method Principle: Most common today; uses a silver/silver chloride reference electrode

Answer 10

Ion-selective electrode

Question 11

Chloride Method Principle: Based on determination of chloride-dependent alpha-amylase activity

Answer 11

Enzymatic (chloride method)

Question 12

*Chloride Method Principle: Pilocarpine iontophoresis

Answer 12

Sweat chloride (iontophoresis)

Question 13

Purposes of the reagents in the sweat chloride test

Answer 13

*

Question 14

What is the historical calcium precipitation method and two specific dyes used in the spectrophotometric method for measuring calcium

Answer 14

Historical method: was precipitation with oxalate (Clark and Collip method)
Spectrophotometric: o-cresolphthalein or arsenazo III

Question 15

Three reagents used in photometric magnesium methods

Answer 15

CalMAGite, formazan, methylthymol blue

Question 16

Reagent used in the most common phosphorus method

Answer 16

*Photometric method: reaction of phosphate ions with ammonium molybdate, measured by UV absorption or reduction to the colored compound molybdenum blue

Question 17

Specimen and anticoagulant interferences for sodium method

Answer 17

1. Can analyze serum, plasma, whole blood, urine, or other
2. No Na in anticoagulant
3. separate serum/plasma from cells within 3 hours

Question 18

Specimen and anticoagulant interferences for potassium method

Answer 18

1. Can analyze serum, plasma, whole blood, urine, or other
2. No K salt in anticoagulant
3. No hemolysis for K
4. separate serum/plasma from cells within 3 hours to prevent K leakage

Question 19

Specimen and anticoagulant interferences for chloride method

Answer 19

1. Serum or heparinized plasma

* *2. sweat chloride by pilocarpine iontophoresis

Question 20

Specimen and anticoagulant interferences for bicarbonate/total carbon dioxide method

Answer 20

1. Serum, heparinized plasma, or whole blood (usually blood gas specimen)
2. Handled anaerobically b/c loss of CO2

Question 21

Specimen and anticoagulant interferences for magnesium method

Answer 21

1. Serum or heparinized plasma

2. NO HEMOLYSIS

Question 22

Specimen and anticoagulant interferences for calcium method

Answer 22

1. Serum or heparinized plasma
2. Promptly separate from cells to prevent uptake of Ca2+ by RBCs
3. CANNOT use anticoagulants such as EDTA, oxalate, or fluoride that chelate or precipitate calcium

Question 23

Specimen and anticoagulant interferences for phosphorus method

Answer 23

1. Serum or heparinized plasma
2. No EDTA or citrate or oxalate anticoagulants as they interfere with formation of phosphomolybdate complex
3. NO HEMOLYSIS
4. Separate from cells promptly

Question 24

Electrolytes for which a hemolyzed specimen is unacceptable

Answer 24

NO HEMOLYSIS:

• K+
• Magnesium
• Phosphorus