Treatment: diuretics (thiazides, loop diuretics, mineralocorticoid receptor antagonists and potassium-sparing diuretics)

Before starting

• Serum electrolytes (sodium, potassium)
• Serum creatinine with eGFR
• Fasting plasma glucose (if diabetes or prediabetes)if neededIn people with diabetes or prediabetes, blood glucose checks are stepped up on a loop diuretic ^[2,3].
• Serum urate (if known gout or hyperuricaemia)if neededDiuretics raise serum urate and can trigger a gout attack in predisposed patients; the hydrochlorothiazide dose is adjusted to serum urate ^[2,4].
• Serum magnesium (if hypokalaemia difficult to correct, or bumetanide combined with a PPI)if neededThiazides and related drugs increase urinary magnesium loss; hypokalaemia with hypomagnesaemia may resist potassium until magnesium is corrected ^[5]. On bumetanide combined with a PPI, serum magnesium is monitored as a precaution ^[3].

Within the week after starting treatment

• Serum electrolytes (sodium, potassium)
• Serum creatinine with eGFR

Before starting

• Serum electrolytes (sodium, potassium)
• Serum creatinine (also calculate Cockcroft–Gault clearance)

One week to 15 days after starting (and after each dose increase)

• Serum electrolytes (sodium, potassium)
• Serum creatinine with eGFR

One month (4 weeks) after starting or after dose adjustment

• Serum electrolytes (sodium, potassium)
• Serum creatinine with eGFR
• Heart failure on spironolactone: then every 4 weeks up to 3 months, every 3 months in the first year, then every 6 months.

Regularly: at least every 1 to 2 years in hypertension, more often depending on the patient's condition (see the note)

• Serum electrolytes (sodium, potassium)
• Serum creatinine with eGFR
• Fasting plasma glucose (if diabetes or prediabetes)if neededIn people with diabetes or prediabetes, blood glucose checks are stepped up on a loop diuretic ^[2,3].
• Serum urate (if known gout or hyperuricaemia)if neededDiuretics raise serum urate and can trigger a gout attack in predisposed patients; the hydrochlorothiazide dose is adjusted to serum urate ^[2,4].

Laboratory tests without waiting

• Serum electrolytes (sodium, potassium)
• Serum creatinine with eGFR