Table 1 Inclusion and exclusion criteria for the BiCARB trial

Inclusion criteria:

Participant is willing and able to give informed consent for participation in the study

Male or female aged 60 years or above

Last known estimated glomerular filtration rate (eGFR) <30 ml/min/1.73 m² by MDRD4 equation

Serum bicarbonate <22 mmol/L

Able (in the investigator’s opinion) and willing to comply with all study requirements.

Exclusion criteria:

Severe cognitive impairment precluding written informed consent

Already taking bicarbonate therapy unless a 3-month washout period is planned

Documented renal tubular acidosis (likely to require bicarbonate, often in very large doses)

On renal replacement therapy (haemodialysis or peritoneal dialysis)

Anticipated to start renal replacement therapy within 3 months

Participant who is terminally ill, as defined as less than 3-months expected survival

Decompensated chronic heart failure (to ensure that fluid overload is not exacerbated by the additional sodium load from the intervention)

Bisphosphonate therapy (to avoid obscuring bone turnover effects; patients with eGFR <30 mL/min/1.73 m² should not usually be taking bisphosphonates as this is a listed contraindication)

Uncontrolled hypertension at screening visit (BP >150/90 mmHg despite use of four agents), unless evidence from home or 24-hour blood pressure monitoring that blood pressure is usually controlled.

Subject participated in another clinical trial (other than observational studies and registries) concurrently or within 30 days prior to screening for entry into this study

Participant has a known allergy to sodium bicarbonate or lactose