The goal of this clinical trial is to predict the progression of chronic kidney disease by diuretic testing in patients with chronic kidney disease. The main questions it aims to answer are:

Does a worse result of a diuretic test predict the progression of chronic kidney disease?

If there is a comparison group: Researchers will compare the diuretic test in patients with chronic kidney disease to healthy participants to see if the results are different in a healthy kidney.

Participants will undergo diuretic testing. This involves the administration of bumetanide and hydrochlorothiazide with subsequent blood and urine collections.

Inclusion Criteria for CKD subjects:

• CKD stage G3 (creatinine-based eGFR 30-59 mL/min/1.73m2) during the last outpatient visit

Inclusion Criteria for Healthy subjects:

• eGFR within the expected range for age (a decline of 1 ml/min/1.73 m2 per year starting from age 40 is considered the normal age-related decline in kidney function

Exclusion Criteria:

• Known intolerance or allergy to the diuretics
• Current systemic chemotherapy for malignancy
• Kidney transplant recipient
• Use of calcineurin-inhibitors
• Life expectancy < 12 months
• Current immunosuppressive treatment for glomerulonephritis
• Incapacitated subjects or subjects who are deemed unfit to adequately adhere to instructions from the research team
• Hypokalemia or hyperkalemia (K+ < 3.0mmol/L or K+ > 5.5 mmol/L) at inclusion visit
• Hypo- or hypernatremia (Na+ < 130 mmol/L or Na+ > 150mmol/L) at inclusion visit
• Inherited tubulopathy as the cause of CKD
• Autosomal dominant polycystic or tubulointerstitial kidney disease causing CKD
• Clinically relevant heart failure (New York Heart Association class III or IV)
• Therapy-resistant hypertension, defined as systolic blood pressure > 180mmHg at the inclusion visit
• Current treatment with inhibitors of Organic anion transporters: probenecid, pravastatin, cimetidine, cephalosporins, acetazolamide [22]
• Active hepatitis during last outpatient visit
• Liver cirrhosis in advanced stage (Child-Pugh B or C)
• Active drug- or alcohol abuse
• Not being able to tolerate a 28-day washout of one of the drugs interfering with diuretic testing.
• Women who are pregnant, breastfeeding, or planning on becoming pregnant before the test day