Disposable urea sensor and system for determining creatinine and urea nitrogen-to-creatinine ratio in a single device

A combination BUN-creatinine sensor comprising:

• a first working electrode for measuring urea having a dissolvable mixture of a BUN reagent matrix disposed directly thereon, wherein said BUN reagent matrix includes urease but absent any redox mediator;
• a second working electrode for measuring creatinine with a creatinine reagent matrix disposed thereon;
• a third working electrode for measuring creatine having a creatine reagent matrix disposed thereon;
• a reference electrode wherein said first working electrode, said second working electrode, said third working electrode, and said reference electrode are formed by a reagent holding layer having a separate cutout for each of said first working electrode containing said BUN reagent matrix, said second working electrode containing said creatinine reagent matrix, said third working electrode containing said creatine reagent matrix, and said reference electrode containing a redox mediator;
• and
• a sample chamber containing said first working electrode, said second working electrode, said third working electrode and said reference electrode.

A method for determining the blood urea nitrogen to creatinine ratio of a blood sample, said method comprising:

• obtaining a combination disposable sensor containing a blood urea nitrogen electrode containing a BUN reagent matrix having urease but absent any redox mediator, creatinine and creatine electrodes, and a reference electrode containing a redox mediator but no urease formed by a reagent holding layer having a separate cutout for each of said blood urea nitrogen electrode, said creatinine and creatine electrodes and said reference electrode, said combination having at least one sample inlet, at least one sample chamber and electrical connection means;
• disposing a portion of said blood sample into said at least one sample chamber;
• measuring the blood urea nitrogen concentration of said blood sample;
• measuring the creatinine concentration of said blood sample;
• and
• determining the blood urea nitrogen to creatinine ratio.