Page 311 - Saunders Comprehensive Review For NCLEX-RN

Drawing blood specimens from an extremity

in which an IV solution is infusing can produce an
inaccurate result, depending on the test being
performed and the type of solution infusing. Prolonged
use of a tourniquet before venous sampling can
increase the blood level of potassium, producing an
inaccurate result.
C. Serum potassium

1. A major intracellular cation, potassium regulates
cellular water balance, electrical conduction in muscle
cells, and acid-base balance.
2. The body obtains potassium through dietary ingestion
and the kidneys preserve or excrete potassium,
depending on cellular need.

3. Potassium levels are used to evaluate cardiac

function, renal function, gastrointestinal function, and
the need for IV replacement therapy.
4. If the client is receiving a potassium supplementation,
this needs to be noted on the laboratory form.
5. Normal reference interval: 3.5 to 5.0 mEq/L (3.5 to
5.0 mmol/L)
6. Elevated values occur in the following: acute kidney
injury or chronic kidney disease, Addison's disease,
dehydration, diabetic ketoacidosis, excessive dietary
or IV intake of potassium, massive tissue destruction,
metabolic acidosis
7. Below normal values occur in the following: Burns,
Cushing's syndrome, deficient dietary intake of
potassium, diarrhea (severe), diuretic therapy, GI
fistula, insulin administration, pyloric obstruction,
starvation, vomiting
8. Clients with elevated white blood cell (WBC) counts
and platelet counts may have falsely elevated
potassium levels.
D. Activated partial thromboplastin time (aPTT)
1. The aPTT evaluates how well the coagulation
sequence (intrinsic clotting system) is functioning by
measuring the amount of time it takes in seconds for
recalcified citrated plasma to clot after partial
thromboplastin is added to it.
2. The test screens for deficiencies and inhibitors of all
factors, except factors VII and XIII.

3. Usually, the aPTT is used to monitor the

effectiveness of heparin therapy and screen for

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