Can a salt substitute save your kidneys after tumor surgery?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Participants must meet all of the following criteria: 1. Voluntary participation with signed informed consent from both the primary participant and all cohabiting family members, with commitment to study procedures and follow-up; 2. Age ≥18 years at enrollment (when signing informed consent), any gender; 3. Diagnosed kidney tumor patients who underwent radical nephrectomy or partial nephrectomy (no restrictions on surgical approach); 4. Preoperative eGFR \>60 ml/min/1.73m² (calculated by CKD-EPI equation); 5. Serum potassium \<4.8 mmol/L; 6. Predominantly home-based dietary habits (\>90% meals prepared at home, assessed via self-report); 7. Normal contralateral renal function at screening; 8. Normal cardiopulmonary and hepatic function: Exclusion Criteria: * Participants will be excluded if they meet any of the following: 1. Participant or cohabiting family members currently using potassium-sparing diuretics or potassium supplements, or prior use of salt substitutes; 2. Post-discharge eGFR \<45 ml/min/1.73m² without significant fluctuation; 3. Comorbid chronic kidney diseases (e.g., diabetic nephropathy, lupus nephritis); 4. Preoperative history of urinary tract obstruction; 5. Cohabiting family member(s) with CKD (eGFR \<45 ml/min/1.73m²); 6. Planned postoperative nephrotoxic medications (e.g., anti-neoplastic agents, immunotherapy); 7. Uncontrolled diabetes (HbA1c ≥12%); 8. Uncontrolled hypertension (seated SBP ≥180 mmHg or DBP ≥110 mmHg), symptomatic hypotension (SBP \<90 mmHg), or clinically evident hypovolemia; 9. Preoperative proteinuria (≥1+ on dipstick); 10. Severe cardiovascular disease (NYHA Class III-IV), gastrointestinal obstruction, or hyperkalemia history; 11. BMI \<18.5 kg/m² or \>30 kg/m²; 12. Participation in another clinical trial ≤30 days before randomization or concurrently; 13. Communication barriers or anticipated non-adherence; 14. Structural/functional urological abnormalities (e.g., duplicated kidneys, polycystic kidneys, renal artery stenosis, stones, BPH) or indwelling catheters; 15. Prior radiotherapy/ablation/surgery on the contralateral kidney; 16. Life expectancy \<6 months (e.g., metastatic renal carcinoma).