Hi, Montelukast Sodium and Levocetirizine (allergy/antihistamine medicines) generally do not interfere with the ARR (Aldosterone-Renin Ratio) test. It's mainly certain BP medicines (like beta-blockers, ACE inhibitors, ARBs, and especially spironolactone) that need to be stopped before this test, not allergy medicines.
Next Steps
Please still inform your endocrinologist about these two medicines before your test, since exact protocols can vary slightly between labs/doctors. You can message or call their clinic to confirm rather than waiting for your next visit, so there's no delay or repeat testing needed.
Health Tips
Don't stop any of your prescribed BP medications on your own before the test — only stop/adjust medicines if your doctor specifically tells you to.