Electrolytes

Question 1

The major cation of extracellular fluid is…

Answer 1

Sodium.

Question 2

___% of sodium is reabsorbed in the kidney tubules.

Answer 2

85.

Question 3

Reference range of sodium.

Answer 3

135 - 145 mmol/L.

Question 4

Conditions associated with decreased sodium levels (hyponatremia).

Answer 4

(1) Diabetic acidosis; (2) Diarrhea; (3) Addison’s Disease; (4) Renal tubular disease.

Question 5

Conditions associated with increased sodium levels (hypernatremia).

Answer 5

(1) Cushing’s syndrome; (2) Dehydration; (3) Hyperaldosteronism (increased renal reabsorption); (4) Insulin treatment of uncontrolled diabetes.

Question 6

Method used for sodium measurement.

Answer 6

Ion-selective electrode (ISE).

Question 7

A direct ISE reading of sodium uses a diluted or undiluted sample?

Answer 7

Undiluted.

Question 8

A indirect ISE reading of sodium uses a diluted or undiluted sample?

Answer 8

Diluted.

Question 9

Pseudohyponatremia is defined and caused by…

Answer 9

Pseudohyponatremia an a false decrease of sodium levels that is caused by high levels of triglycerides or protein.

↑↑ protein/triglycerides; ↓ sodium.

Question 10

The major cation of intracellular fluid is…

Answer 10

Potassium.

Question 11

Reference range of potassium.

Answer 11

3.5 - 4.0 mmol/L.

Question 12

What preanalytical factors may cause a false increase in potassium (pseudohyperkalemia)?

Answer 12

(1) Hemolysis; (2) EDTA contamination.

Question 13

Hypo- or hyperkalemia may cause what conditions?

Answer 13

Heart arrhythmias and/or neuromuscular symptoms.

Question 14

Hypokalemia conditions include…

Answer 14

(1) Insulin injections; (2) alkalosis; (3) GI losses (vomiting or diarrhea); (4) Hyperaldosteronism; (5) Cushing’s syndrome.

Question 15

Hyperkalemia conditions include…

Answer 15

(1) Diabetic acidosis (metabolic); (2) Intravascular hemolysis; (3) Severe burns; (4) Renal failure; (5) Addison’s disease.

Question 16

Testing method for potassium…

Answer 16

Ion-selective electrode.

Question 17

Major anion of extracellular fluid is…

Answer 17

Chloride.

Question 18

The function of chloride is…

Answer 18

Maintains hydration, osmotic pressure, and the normal anion-cation balance.

Question 19

Reference range of chloride.

Answer 19

98 - 106 mmol/L.

Question 20

Chloride levels generally trend the same direction as ___.

Answer 20

Sodium.

Question 21

Hypochloremia conditions include…

Answer 21

(1) Diabetic acidosis (excessive acid production); (2) Chronic pyelonephritis; (3) Prolonged vomiting; (4) Aldosterone deficiency.

Question 22

Hyperchloremia conditions include…

Answer 22

(1) Prolonged diarrhea (excess bicarbonate loss); (2) Renal tubular acidosis; (3) Adrenocortical hyperfunction.

Question 23

Testing method for chloride is…

Answer 23

Ion-selective electrode.

Question 24

Sweat chloride testing is elevated in what condition?

Answer 24

Cystic fibrosis; >60 mmol/L.

Question 25

Describe the anion gap.

Answer 25

Calculation that reflects that differences between unmeasured cations and anions; used as analytical QC for measuring all electrolytes. If abnormal gaps for multiple patients, suspect problem with electrolyte measurements.

Question 26

What are the major unmeasured cations for the anion gap calculation?

Answer 26

Calcium, magnesium, and potassium.

Question 27

What are the major unmeasured anions of the anion gap calculation?

Answer 27

Albumin, sulfate, and phosphate.

Question 28

What is the calculation of the anion gap WITH potassium?

Answer 28

[(Na)+(K)]-[(Cl)-(HCO3)]

Question 29

What is the calculation of the anion gap WITHOUT potassium?

Answer 29

(Na) - (Cl) + (HCO3)

Question 30

Reference range of anion gap (with K).

Answer 30

10-20 mmol/L.

Question 31

Reference range of anion gap (without K).

Answer 31

7-16 mmol/L.

Question 32

An increased anion gap is indicative of an increased concentration of what three unmeasured anions?

Answer 32

(1) Ethanol; (2) Ketones; (3) Lactic acid.

Question 33

A increased anion gap is indicative of an decreased concentration of what two unmeasured cations?

Answer 33

Low serum Mg and Ca.

Question 34

A decreased anion gap is indicative of a decreased concentration of what unmeasured anion?

Answer 34

Albumin.

Question 35

A decreased anion gap is indicative of an increased concentration of what three unmeasured cations?

Answer 35

Mg, Ca, and Lithium therapy.

Question 36

Define osmolality.

Answer 36

The measure of total concentration of dissolved particles in a solution.

Question 37

Osmolality can be measured directly using what two testing methods?

Answer 37

Freezing point depression and vapor pressure depression.

Question 38

What is the equation to determine calculated osmolality?

Answer 38

2Na + (Glucose/18) + (BUN/2.8)

Question 39

A measured osmolality is 10x higher than calculated osmolality indicates the presence of what?

Answer 39

Exogenous unmeasured anions (methanol, ethanol, ketone bodies, etc).

Question 40

The function of magnesium is...

Answer 40

Calcium channel blocking agent (affects heart).

Question 41

Magnesium is increased in...

Answer 41

Renal failure.

Question 42

Magnesium is decreased in...

Answer 42

(1) Cardiac disorders; (2) Diabetes mellitus; (3) Diuretics, alcohol, and other drugs.

Question 43

Testing methods used for magnesium determination.

Answer 43

Atomic absorption and colorimetric method.

Question 44

Function of calcium is...

Answer 44

Combines with phosphate in bone.

Question 45

What three hormones control calcium levels?

Answer 45

(1) PTH; (2) Calcitonin; (3) Vitamin D

Question 46

Hypercalcemia conditions include...

Answer 46

(1) Hyperparathyroidism; (2) Cancer with bone metastasis; (3) Multiple myeloma; (4) Renal failure.

Question 47

Hypercalcemia conditions include...

Answer 47

(1) Hypoparathyroidism; (2) ↓ serum albumin; (3) ↓ vitamin D.

Question 48

Testing methods for calcium include...

Answer 48

(1) Atomic absorption spectroscopy (reference method); (2) Colorimetric method (common); (3) ISE.

Question 49

What preanalytical factor may cause a false decrease in calcium?

Answer 49

EDTA contamination.

Question 50

In cases of Tetany, suspect ___ first, then magnesium of potassium.

Answer 50

Calcium.

Question 51

The majority of phosphate in the body is expressed as phosphorous; laboratory measures ___ only.

Answer 51

inorganic phosphorus (PO4).

Question 52

Phosphorous has an inverse relationship with ___.

Answer 52

Calcium; as Calcium ↑, phosphorous ↓.