Lab Values & ABGs Practice Test #1: Electrolytes

Answer: B. Take the medication with your meals.

Rationale: Phosphate binders work inside the gut. They bind the phosphorus in food so it leaves in the stool instead of being absorbed, so they must be taken with meals (follow the exact timing the prescriber or pharmacist gives). Taken on an empty stomach or hours after eating, there is little phosphorus to bind. Dairy, processed meats, and dark colas are high in phosphorus and are usually limited in kidney disease. A typical adult phosphorus range is about 3.0 to 4.5 mg/dL, though ranges vary by lab. In kidney disease, a high phosphorus level tends to pull the calcium level down, so the nurse also watches for signs of low calcium.

Answer: D. Potassium 3.1 mEq/L

Rationale: Low potassium increases the effect of digoxin on the heart and raises the risk of digoxin toxicity, even when the digoxin level is within the usual range. Loop diuretics such as furosemide cause potassium loss, so this combination needs close monitoring. Nausea and yellow-green vision changes are classic signs of toxicity. The nurse holds the dose according to facility policy and reports both the symptoms and the potassium result; a digoxin level may be ordered. The sodium and calcium values are within typical adult ranges (ranges vary by lab), and a glucose of 132 mg/dL does not affect digoxin. Low magnesium and high calcium also increase toxicity risk.

Answer: A. Confirm the client has adequate urine output, then infuse the dose on an IV pump at the prescribed rate.

Rationale: IV potassium is a high-alert medication. It is never given by IV push or undiluted, because a rapid rise in potassium can cause fatal dysrhythmias and cardiac arrest. It is given diluted, usually as a premixed bag, on an infusion pump at the rate the prescriber and facility policy allow. The kidneys remove potassium, so the nurse checks urine output first; poor output means the potassium can build up. Adding potassium to a hanging bag risks uneven mixing and a concentrated bolus. Gravity infusion cannot control the rate. The nurse also watches the IV site for burning and phlebitis and uses cardiac monitoring when policy requires it.

Answer: C. Calcium gluconate IV

Rationale: When high potassium is already changing the ECG, the first goal is to protect the heart. IV calcium stabilizes the heart muscle cell membranes within minutes and lowers the risk of a lethal dysrhythmia. It does not lower the potassium level. Regular insulin with dextrose works next by shifting potassium into the cells, and the nurse monitors blood glucose closely afterward for hypoglycemia. Potassium binders and diuretics remove potassium from the body but act more slowly. Dialysis may be needed if the kidneys cannot clear potassium. Exact drugs and doses follow the provider's orders and facility protocol.

Answer: B. Report the result to the health care provider and anticipate a repeat blood sample.

Rationale: When red blood cells break open (hemolysis) in the tube, they release potassium, which can make the result falsely high. This is called pseudohyperkalemia. A tight tourniquet left on too long and repeated fist clenching during the draw can do the same. The nurse still reports the result, because a high potassium is never ignored, and anticipates a repeat sample, drawn carefully, before treatment is started. The client is stable with a normal rhythm, so emergency calcium is not indicated on this result alone. Stopping all oral intake and diet changes do not address a falsely high result.

Answer: D. Start seizure precautions.

Rationale: In SIADH the body holds on to water, which dilutes the sodium. When sodium falls this low, water moves into brain cells, causing confusion, headache, and seizures, so seizure precautions are a priority. SIADH is usually managed with a fluid restriction as prescribed, so encouraging extra water would make it worse. A hypotonic fluid such as 0.45% sodium chloride adds free water and can lower the sodium further. A low-sodium diet is not appropriate. If hypertonic saline is prescribed for severe symptoms, the nurse checks sodium levels as often as ordered, because correcting sodium too quickly can cause osmotic demyelination syndrome. The safe rate of correction is set by the provider.

Answer: A. Dry, sticky mucous membranes and restlessness

Rationale: High sodium from water loss or poor intake pulls water out of cells, including brain cells. Expected findings include dry, sticky mucous membranes, restlessness, agitation or confusion, and sometimes a low-grade fever. Older adults are at higher risk because their sense of thirst is weaker and they may depend on others for fluids. A positive Chvostek sign suggests low calcium or low magnesium. Abdominal distention with diminished bowel sounds suggests low potassium. Flushing with absent reflexes suggests high magnesium. Fluid replacement is given as prescribed and the sodium is brought down gradually, because a rapid drop can cause brain swelling.

Answer: C. Spasm of the hand and wrist (Trousseau sign)

Rationale: In pancreatitis, calcium binds to areas of fat breakdown in the abdomen, so the blood calcium level drops. Low calcium makes nerves and muscles more excitable. Inflating a blood pressure cuff above systolic pressure for a few minutes can cause a carpal spasm, called the Trousseau sign. Other signs include tingling around the mouth and fingers, muscle cramps, a positive Chvostek sign, a prolonged QT interval, laryngospasm, and seizures. Muscle weakness with decreased reflexes fits high calcium. Peaked T waves fit high potassium. Total calcium also falls when albumin is low, so the provider may check an ionized calcium to confirm a true deficit.

Answer: A. Encourage oral fluids unless restricted, and help the client walk as tolerated.

Rationale: Cancer in the bone breaks bone down and releases calcium into the blood. High calcium causes constipation, fatigue, muscle weakness, confusion, kidney stones, and dysrhythmias such as a shortened QT interval. Fluids help dilute the calcium and help the kidneys clear it, unless the client has a fluid restriction such as with heart failure. Weight-bearing activity slows the release of calcium from bone, while bed rest speeds it up. Extra dairy adds calcium, and IV calcium is the treatment for low calcium, not high. The provider may also prescribe IV fluids and medications that lower calcium, and the nurse monitors heart rhythm and mental status.

Answer: C. Magnesium

Rationale: Low magnesium causes the kidneys to keep losing potassium, so a low potassium often will not correct until magnesium is replaced as well. Alcohol use disorder is a common cause of low magnesium because of poor intake, vomiting or diarrhea, and kidney losses. Signs of low magnesium include tremors, brisk reflexes, positive Chvostek and Trousseau signs, and dysrhythmias such as torsades de pointes. Phosphorus is also often low in alcohol use disorder, but it does not explain potassium that will not rise. Sodium and glucose do not cause this pattern. The nurse reports the result so the provider can order magnesium replacement.