Potassium

Question 1

Potassium (K+)

Answer 1

• major intracellular cation,
• In cells and RBC average concentration is 150mmol/L and 105mmol/L respectively

Question 2

Increased intracellular K+ are maintained by:

Answer 2

• Na+ and K+ (atp) pump

Question 3

What happens to K+ ions when pump activity decreases

Answer 3

• K+ diffuse out of the cell into the ECF and plasma

Question 4

Excess potassium is excreted by which organ

Answer 4

• kidneys

Question 5

What hormone is responsible for excretion and reabsorption of K+ in exchange for Na+

Answer 5

• aldosterone

Question 6

Specimen requirements for K+ determination

Answer 6

1. Serum or plasma must be collected with minimal hemolysis to avoid contamination from RBC intracellular K
2. Whole blood samples should be kept at 4 degrees b4 separation
3. Severe leukocytes
4. Skeletal muscle activity causes K+ efflux from muscle cells into plasma causing potassium level elevation

Question 7

Why should blood samples be kept at 4 degrees Celsius b4 separation?

Answer 7

• to prevent glycolysis
• The energy-dependent Na+, K+- ATP can’t maintain the Na+/K+ gradient

Question 8

Clinical significance or conditions

Answer 8

• Hypokalemia associated with gastrointestinal loss thru vomiting, diarrhea, gastric suction, intestinal tumor, malabsorption, cancer therapy
• Renal loss through diuretics the, nephritis, renal acidosis and hyperaldosteronism
• Cellular shift due to acidosis, chemotherapy, muscle/cellular injury
• Artifactual due to sample hemolysis

Question 9

Reference intervals of potassium

Answer 9

• Serum= 3.5-5.1 mmol/L
• Plasma= males 3.5-4.5mmol/L
  Females 3.4- 4.4mmol/L
• Urine ( 24hr)= 25-125mmol/L

Question 10

Determination of Na+ and K+

Answer 10

1. Flame emission spectrophometry
2. Spectrophometry essays
3. Ion selective electrodes

Question 11

Flame emission spectrophometry principle

Answer 11

1. Samples are diluted in a diluent containing known amounts of Lithium or cesium and are aspirated into a propane air flame
2. Li and Cs ions when excited they emit spectra with sharp bright lines at 671 and 852 nm respectively
3. Lights emitted from the excited ions is directed through separate photo detectors
4. The Li+ or Cs+ emission signal is used as an internal standard against which the Na+ and K+ signals are compared

Question 12

categories of Spectrophometric methods

Answer 12

1. Based on enzyme activation
2. Kinetic Spectrophometric essays
3. Those that detect the spectral shift produced when Na+bor K+ binds to a macrocyclic chromophore

Question 13

Kinetic Spectrophometric essays are based on what?

Answer 13

1. Activation of the enzyme B-galactosidase by Na+

Question 14

What does the enzyme B-galactosidase hydrolyze?

Answer 14

1. O-nitrophenol-B-d_galactosidase

Question 15

ion selective electrodes

Answer 15

• ISE method uses a semipermeable membrane to develop an electric potential
  produced by having different ion concentrations on either side of the membrane.
• Two electrodes are used; one electrode has a constant potential, making it the
  reference electrode.
• The difference in potential between the reference and measuring electrodes is used
  to calculate the “concentration” of the ion in solution
• Analyzers fitted with ISEs usually contain Na+ electrodes with glass membranes and
  K+ electrodes with liquid ion-exchange membranes that incorporate valinomycin
• The change in electromotive force in a circuit between a measurement
  electrode (the ISE) and a reference electrode is measured
• Most blood gas analyzers are capable of measuring sodium and potassium
• Indirect ISE methods, uses diluted samples
• Direct ISE methods, uses undiluted samples
• Errors are observed due to lack of selectivity, repeated protein coating and
  contamination of the membrane with competing ions