Which laboratory value should a nurse assess before starting therapy with captopril in a diabetic patient diagnosed with hypertension?

Before initiating therapy with captopril in a diabetic patient with hypertension, it is essential to assess serum potassium levels. Captopril is an angiotensin-converting enzyme (ACE) inhibitor that can lead to an increase in serum potassium due to its effect on the renin-angiotensin-aldosterone system. In patients, especially those with diabetes, there is an increased risk of hyperkalemia, which can be life-threatening.

Monitoring serum potassium is crucial because elevated levels can lead to severe cardiac problems, such as arrhythmias or even cardiac arrest. Given that diabetic patients may also have kidney function alterations, the risk of hyperkalemia is further amplified. Therefore, assessing serum potassium levels prior to starting therapy with captopril allows for the prevention of potential complications associated with increased potassium levels.

Other laboratory values, such as serum calcium, blood glucose, and serum magnesium, do not pose the same immediate concerns related to the start of captopril therapy in this context, making potassium monitoring the most critical step before treatment initiation.