An adult with arthritis has been receiving treatment with naproxen and now reports ongoing stomach pain, increasing weakness, and fatigue. Which laboratory test should the nurse monitor?

Choice A: Blood alcohol level of 0.09% (90 mmol/L) is not the most important finding for the nurse to report, as this is within the reference range and does not indicate alcohol intoxication or withdrawal, which can affect the client's mental status and mood stability. This is a distractor choice.

Choice B: Six hours of sleep in the past three days is not the most important finding for the nurse to report, as this is a common symptom of bipolar disorder during manic episodes and does not require immediate intervention by the health care provider. This is another distractor choice.

Choice C: Serum lithium level of 1.6 mEq/L (1.6 mmol/L) is the most important finding for the nurse to report, as this indicates lithium toxicity, which can cause neurological and renal impairment and potentially fatal complications such as seizures, coma, and cardiac dysrhythmias. Therefore, this is the correct choice.

Choice D: Weight loss of 10 pounds (4.5 kg) in past month is not the most important finding for the nurse to report, as this may be related to decreased appetite or increased activity during manic episodes and does not pose an immediate threat to the client's health or safety. This is another distractor choice.

Choice A: Obtain a blood pressure reading before the client gets out of bed. This is the most important intervention, as it can prevent or detect orthostatic hypotension, which is a drop in blood pressure when changing position from lying to standing. Orthostatic hypotension can cause dizziness, fainting, or falls, and it can be caused by medications, dehydration, or cardiac problems.

Choice B: Monitor and record the client's urinary output every day. This is not the most important intervention, as it does not address the client's anxiety or adjustment issues. The urinary output should be monitored for signs of fluid balance, kidney function, or infection, but it is not a priority for this client.

Choice C: Provide the client with teaching regarding a cardiac diet. This is not the most important intervention, as it does not address the client's anxiety or adjustment issues. The cardiac diet should be taught to promote heart health, lower cholesterol, and reduce sodium intake, but it is not a priority for this client.

Choice D: Assess the client's vital signs every 4 hours when awake. This is not the most important intervention, as it does not address the client's anxiety or adjustment issues. The vital signs should be assessed for signs of infection, pain, or hemodynamic instability, but they are not a priority for this client.