Is it necessary to control labs, such as kidney function, liver enzymes, electrolytes, and Thyroid-Stimulating Hormone (TSH), when initiating hypertension pharmacotherapy?

Laboratory Monitoring When Initiating Hypertension Pharmacotherapy

Yes, baseline laboratory testing is necessary before initiating antihypertensive medications, and follow-up labs should be checked within 2-4 weeks after starting or adjusting therapy. 1

Required Baseline Laboratory Tests

The following labs must be obtained before starting antihypertensive therapy:

• Complete Blood Count (CBC) - establishes baseline values before medications that may affect blood counts 2
• Comprehensive Metabolic Panel (CMP) including:
  • Serum electrolytes (sodium, potassium, calcium, magnesium) 1
  • Blood urea nitrogen (BUN) and serum creatinine to assess kidney function 1
  • Fasting blood glucose (or glycohemoglobin) 1
  • Liver function tests 1
• Thyroid-Stimulating Hormone (TSH) - identifies thyroid disorders as secondary causes of hypertension 1, 2
• Urinalysis - screens for proteinuria and kidney disease 1
• Lipid profile - for cardiovascular risk stratification 1

Post-Initiation Monitoring Schedule

Within 2-4 Weeks of Starting or Adjusting Medications

Check a basic metabolic profile (electrolytes and kidney function) within 2-4 weeks after initiating or titrating any antihypertensive medication that affects electrolytes or renal function. 1

This is particularly critical for:

• Thiazide diuretics - check electrolytes and eGFR within 4 weeks of initiation or dose escalation due to risks of hypokalemia, hyponatremia (especially in elderly), and hyperuricemia 1, 3
• ACE inhibitors/ARBs - monitor for hyperkalemia and changes in renal function, as these drugs can cause increases in BUN and creatinine, particularly in patients with renal artery stenosis or pre-existing renal impairment 4
• Combination therapy - when using multiple agents that affect electrolytes 1

Monthly Follow-Up Until Blood Pressure Goal Achieved

• Clinical follow-up every 6-8 weeks (or monthly per WHO guidelines) until BP target is safely achieved 1
• Home blood pressure monitoring to avoid hypotension (SBP <110 mmHg) 1
• Assessment of adherence, adverse effects, and orthostatic hypotension 1

After Blood Pressure Control Achieved

• Laboratory monitoring and clinic follow-up every 3-6 months, depending on medications used and patient stability 1
• For patients with CKD Stage 2, reassess eGFR and UACR every 6-12 months 5
• Monitor electrolytes every 6-12 months, or more frequently if on RAS inhibitors or mineralocorticoid receptor antagonists 5

Medication-Specific Monitoring Requirements

Thiazide Diuretics (Hydrochlorothiazide, Chlorthalidone)

• Electrolytes within 4 weeks - hypokalemia occurs commonly; hyponatremia risk is heightened in elderly patients 1, 3
• Kidney function - chlorthalidone can still be effective even with eGFR <30 mL/min/1.73m², but requires close monitoring 1, 6
• Do not automatically discontinue thiazides when eGFR decreases to <30 mL/min/1.73m²; assess risks and benefits individually 1
• Watch for hyperuricemia and potential gout precipitation 3

ACE Inhibitors/ARBs (Enalapril, Candesartan)

• Kidney function within 2-4 weeks - can cause increases in BUN and creatinine, especially with bilateral renal artery stenosis (occurs in 20% of such patients) 4
• Potassium monitoring - hyperkalemia (>5.7 mEq/L) occurs in approximately 1% of hypertensive patients 4
• Avoid potassium supplements and salt substitutes containing potassium without physician consultation 4
• Risk factors for hyperkalemia include renal insufficiency, diabetes, and concomitant use of potassium-sparing diuretics 4

Calcium Channel Blockers

• Generally require less intensive laboratory monitoring 7
• Standard metabolic panel within 2-4 weeks is still reasonable 1

Critical Safety Considerations

When to Check Labs More Frequently

• Pre-existing renal impairment - more likely to develop increases in BUN and creatinine 4
• Elderly patients - heightened risk of hyponatremia with thiazides 1
• Diabetes mellitus - increased risk of hyperkalemia with ACE inhibitors/ARBs 4
• Volume depletion states - patients should hold or reduce medications during vomiting, diarrhea, or decreased oral intake to prevent acute kidney injury 1

Warning Signs Requiring Immediate Laboratory Assessment

Patients should be instructed to contact their physician if they experience symptoms of electrolyte imbalance: 3

• Excess thirst, tiredness, drowsiness, restlessness
• Muscle pains or cramps
• Nausea or vomiting
• Increased heart rate or pulse
• Dryness of mouth, weakness, lethargy

Common Pitfalls to Avoid

• Do not skip baseline labs - they are essential for medication selection, dosing, and identifying secondary causes of hypertension 1, 2
• Do not assume thiazides are ineffective in advanced CKD - chlorthalidone can reduce blood pressure even with eGFR <30 mL/min/1.73m², but requires electrolyte monitoring 1, 6
• Do not forget to recheck labs after dose adjustments - not just at initial start 1
• Do not use potassium-sparing diuretics with ACE inhibitors/ARBs without very close potassium monitoring due to severe hyperkalemia risk 4