Lab Values & ABGs Practice Test #6: Mixed Lab Priorities

Answer: C. Make sure the repeat troponin is drawn at the time set by the chest pain protocol, and keep the client on a cardiac monitor

Rationale: Troponin is released when heart muscle is injured, but the level can take a few hours to rise after symptoms start. One normal result drawn early cannot rule out a myocardial infarction, so troponin is measured serially. The repeat timing depends on the assay and the facility's protocol (often 1 to 3 hours with a high-sensitivity test, longer with older tests), so follow the protocol and the provider's prescription. Keep the client on a monitor and reassess pain and the ECG while waiting. Option A is wrong because a single early normal value is not enough to rule out a heart attack. Option B is wrong because CK-MB is less specific to the heart than troponin and has largely been replaced by it. Option D is wrong because aspirin for suspected acute coronary syndrome is given as prescribed without waiting for an abnormal troponin, unless the client has a contraindication.

Answer: A. Hold the next lithium dose and notify the health care provider right away

Rationale: Lithium has a narrow therapeutic range. A commonly used maintenance range is about 0.6 to 1.2 mEq/L, but target ranges differ by lab, by prescriber and by phase of treatment, so check your facility's values. A level of 2.1 mEq/L together with a coarse tremor and an unsteady gait points to lithium toxicity. Vomiting and diarrhea cause fluid and sodium loss, and the kidneys then hold on to more lithium, so levels rise. The nurse holds the next dose and notifies the provider promptly; the client may need IV fluids, close neurological checks and repeat levels. Option B is wrong because giving another dose adds to the toxicity. Option C is wrong because a low-sodium diet makes the kidneys keep more lithium and raises the level further; clients are taught to keep salt and fluid intake steady. Option D is wrong because a toxic level with symptoms needs action now, not in a week.

Answer: D. Serum potassium 3.0 mEq/L

Rationale: Using typical adult ranges (potassium about 3.5 to 5.0 mEq/L; check your lab's values), a potassium of 3.0 mEq/L is low. Furosemide is a loop diuretic that causes potassium loss. Low potassium makes the heart muscle irritable and raises the risk of dysrhythmias, and anesthesia and surgical stress add to that risk. The nurse reports it before surgery so the surgeon and anesthesia provider can decide whether to replace potassium or delay the case. Option A is wrong because a hemoglobin of 13.2 g/dL is within typical adult ranges. Option B is wrong because a fasting glucose of 104 mg/dL is only slightly above the usual fasting range and is not a reason to hold surgery. Option C is wrong because a platelet count of 190,000/mm³ is within the typical range of about 150,000 to 400,000/mm³.

Answer: B. The high lactate suggests the tissues are not getting enough oxygen, and a repeat lactate will help show whether treatment is working

Rationale: Lactate builds up when cells switch to anaerobic metabolism because they are not getting enough oxygen, as happens with low blood pressure and poor perfusion in sepsis. Many labs report a typical value below about 2 mmol/L (check your lab). A lactate of 4.4 mmol/L with hypotension is a red flag for septic shock. Sepsis guidelines call for remeasuring an elevated lactate to judge the response to treatment such as IV fluids, which are given in the volume and rate the provider and protocol direct. Option A is wrong because fever alone does not explain this level, and ignoring it delays treatment. Option C is wrong because creatinine and urine output, not lactate, are used to judge kidney function. Option D is wrong because lactate is an acid; a high lactate causes metabolic acidosis, and fast breathing is the body's attempt to compensate.

Answer: A. Write down the result, then read it back to the caller along with the client's two identifiers to confirm it

Rationale: Critical results must reach the person who can act on them quickly and accurately. When a result is given by phone, the nurse writes it down and reads it back, with the client's name and a second identifier, so the caller can confirm it is correct. This read-back step is a national patient safety practice for verbal reports of critical results. Next, the nurse assesses the client (including the cardiac rhythm), notifies the provider within the time frame set by facility policy and documents who was told, when and what was done. Option B is wrong because waiting delays treatment of a dangerous value. Option C is wrong because the nurse who receives the call is responsible for passing it on; the lab cannot take that over unless facility policy says so. Option D is wrong because potassium needs a prescription, and the dose and route are the provider's decision.

Answer: C. A client 18 hours after a total thyroidectomy whose calcium is 7.1 mg/dL and who reports tingling around the mouth and in the fingertips

Rationale: The parathyroid glands sit next to the thyroid and can be injured or removed during a thyroidectomy, which causes calcium to fall. A total calcium of 7.1 mg/dL is low (a typical adult range is about 8.5 to 10.5 mg/dL; check your lab, and interpret it with the albumin level). Tingling around the mouth and in the fingertips shows the low calcium is already affecting nerves, and it can progress to tetany, laryngospasm and seizures. This client is unstable and needs assessment, a call to the provider and IV calcium as prescribed, with airway equipment nearby. Option A is wrong because a stable, expected potassium in a client already scheduled for dialysis is not the most urgent. Option B is wrong because a falling white cell count shows the infection is improving. Option D is wrong because a sodium of 134 mEq/L is only slightly low and the client has no symptoms.

Answer: B. Give IV fluids as prescribed and monitor urine output and serum potassium closely

Rationale: A very high CK after a long time lying down points to rhabdomyolysis, the breakdown of skeletal muscle. CK reference ranges vary by lab, but this result is many times the upper limit. Damaged muscle releases myoglobin, which turns the urine dark and can injure the kidneys, and it also releases potassium into the blood. Treatment centers on IV fluids to flush the kidneys, given at the volume and rate the provider prescribes. The nurse monitors urine output, kidney function and potassium closely and watches the cardiac rhythm. Option A is wrong because restricting fluids increases the risk of acute kidney injury. Option C is wrong because activity can worsen muscle injury; the priority now is fluids and monitoring. Option D is wrong because muscle breakdown tends to raise potassium, so a supplement could cause dangerous hyperkalemia.

Answer: D. Give 15 to 20 g of fast-acting carbohydrate, such as 4 oz (120 mL) of juice, and recheck the glucose in 15 minutes

Rationale: A glucose below 70 mg/dL is hypoglycemia, and this client has symptoms. Because the client is alert and can swallow safely, the first action is fast-acting carbohydrate by mouth. Diabetes guidelines suggest 15 to 20 g of glucose, then a recheck in about 15 minutes, repeating if the glucose is still low; once it is back in range, the client eats a meal or snack. Follow your facility's hypoglycemia protocol, which sets the exact amounts and when to call the provider. Option A is wrong because waiting lets the glucose keep falling; most facilities have a standing protocol so the nurse can treat at once. Option B is wrong because fat and protein slow the absorption of sugar, so they do not correct a low quickly. Option C is wrong because an hour is too long to wait with a symptomatic low.

Answer: C. The rise in BNP reflects more stretch on the ventricles from fluid overload, which fits worsening heart failure

Rationale: The ventricles release BNP when they are stretched by extra volume and pressure. A sharp rise from the client's own earlier level, along with rapid weight gain and new crackles, fits fluid overload and worsening heart failure. The trend matters more than one number, because cut-offs differ between BNP and NT-proBNP tests and are affected by age, kidney function and obesity. Sacubitril/valsartan also raises BNP (but not NT-proBNP), so check the medication list. Option A is wrong because troponin, not BNP, is the marker of heart muscle injury. Option B is wrong because BNP rises with too much fluid, not too little. Option D is wrong because kidney disease can raise BNP, but the level still reflects strain on the heart and is used in heart failure care.

Answer: A. Report the mismatch and ask for a new sample drawn from the arm without the IV infusion

Rationale: A result that does not fit the client should be questioned before it is treated. Blood drawn from the same arm as a running infusion, especially above the IV site, can be mixed with the IV fluid. Dextrose in the bag falsely raises the glucose and can also change electrolyte results. The alert client with no symptoms and a normal fingerstick strongly suggest a contaminated sample. The nurse reports the mismatch and has the test repeated from the other arm (or following the facility's policy for drawing near an infusion). Option B is wrong because giving insulin for a false high could cause dangerous hypoglycemia. Option C is wrong because the infusion was prescribed and is not the problem; only the sampling site is. Option D is wrong because a glucose of 486 mg/dL is not an expected effect of maintenance IV dextrose in a client without diabetes and should not be accepted without checking.