This is an open, prospective, and interventional study investigating the potassium measurement with the CardioRenal device in capillary blood. It will be conducted at one investigational site.

Each subject will have capillary blood collections. Additionally as a reference a venous blood collection will be conducted

Cardiorenal is a company aiming to develop in-vitro diagnostic medical devices to measure the potassium from a single drop of capillary blood to allow an everyday home monitoring of the potassium value like with the diabetes patients who supervise their blood sugar level by measurements with glucose-test stripe from a drop of capillary blood.

A major problem for the blood potassium monitoring at clinical levels is caused by hemolysis leading to the overestimation of potassium level. Hemolysis is the lysis of red blood cells (RBC, erythrocytes) and the release of their contents into plasma. The hemolysis may occur from in vivo or in vitro causes (milking, pressure…). It has also been reported that capillary puncture may induce increased level of hemolysis compared to venous sampling.

CardioRenal aims to limit those factors to guarantee an accurate measurement of potassium concentration in a capillary sample by using a standardized method of capillary pricking.

After clarification the approval the Informed Consent is signed and the inclusion as well as exclusion criteria (incl. demography, concomitant medication and medical history) or vital parameters (weight), are raised.

With 40 healthy subjects capillary and venous blood is taken. Blood is taken from the subject by trained specialist staff. The capillary blood sampling occurs in 400 µl Lithium-Heparin BD vacutainer Microtainers.

• A total of <1mL volume of capillary blood is taken.
• In addition 10 ml blood from the vein of a forearm is taken.

With 30 hemodialysed subjects capillary and venous blood is taken before and/or after dialysis session to extend the potassium concentration range. Blood is taken from the subject by trained specialist staff. The capillary blood sampling occurs in 400 µl Lithium-Heparin BD vacutainer Microtainers.

• A screening based on potassium measurement just before the capillary puncture is performed to test the eligibility of the subject : a 2.5mL blood is taken from the fistula or the central venous catheter.
• A total of <1mL volume of capillary blood is taken.
• In addition 10 ml blood from the fistula or the central venous catheter.

To guarantee a light blood decrease without strong mechanical pressure, the site for capillary puncture are warmed up before the capillary sampling during 2 minutes before puncture.

Inclusion Criteria:

• Adults (Age Over 18 yo)
• Healthy volunteers
• Chronic Hemodialysed patients
• Pre-dialysis patient, taken off after the long interdialytic interval (> 2 days)
• AND with a K+ > 5.0 mmol/L just before starting the dialysis session (screening checked on venous or arterio-venous blood sample)
• Post-dialysis, in patients treated with a 2 mmol/l dialysis bath
• AND with a K+ < 3.5 mmol/L at the end of the dialysis session (screening checked on venous or arterio-venous blood sample)

Exclusion Criteria:

• No consent
• Age <18 yo
• Medical history of crisis (epilepsy)
• Known inherited hemolytic anemia
• Autoimmune hemolytic anemia
• Infectious Hemolytic anemia
• Prosthetic Cardiac valves
• Hemolytic uremic syndrome
• Peripheral edema
• Dehydration
• Peripheral Arterial Obstructive Disease (PAOD)
• Raynaud syndrome
• Known evolutive cancers
• Vulnerable patients, patients deprived from liberty and patients with a physical or mental state altered by disease, age or disability which impacts their ability to defend their interests and for which protection measures are taken