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

1. A system for determining the urea nitrogen to creatinine ratio in a sample, said system comprising:

a disposable urea sensor comprising a laminated body having a fluid sample inlet end and an electrical contact end, said laminated body includes a base layer, a reagent holding layer with cutouts defining a working electrode and a reference electrode, a channel forming layer, and a cover, and a dissolvable mixture of a urea reagent matrix disposed in a cutout and directly on said working electrode wherein said urea reagent matrix contains urease but absent any redox mediator;

a disposable creatinine sensor attached to said disposable urea sensor;

means for determining a urea concentration in a portion of said sample using said disposable urea sensor;

means for determining a creatinine concentration in a portion of said sample using said disposable creatinine sensor; and

means for using said urea concentration and said creatinine concentration to determine said urea nitrogen to creatinine ratio of said sample.

2. The system of claim 1 wherein said urea reagent matrix further includes one or more of a material selected from the group consisting of a binder, a buffer, a surfactant, a stabilizer, and an bulking reagent.

3. 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.

4. The combination sensor of claim 3 wherein said BUN reagent matrix further includes one or more of a material selected from the group consisting of a binder, a buffer, a surfactant, a stabilizer, and a bulking reagent.

5. 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.

6. The method of claim 5 wherein said obtaining step further includes making a disposable blood urea nitrogen sensor, making a disposable creatinine sensor and attaching said disposable blood urea nitrogen sensor to said disposable creatinine sensor in a back-to-back configuration.

7. The method of claim 5 wherein said obtaining step further includes obtaining a base layer having a plurality of electrically conductive paths on opposite sides of said base layer and assembling a blood urea nitrogen sensor and a reference electrode on one side of said base layer and assembling a creatinine sensor and a reference electrode on an opposite side of said base layer.

8. The method of claim 5 wherein said obtaining step further includes obtaining a base layer having a plurality of electrically conductive paths on one side of said base layer, assembling said blood urea nitrogen sensor and said reference electrode using at least two conductive paths of said plurality of electrically conductive paths and assembling a creatinine sensor using at least two other conductive paths of said plurality of electrically conductive paths wherein said blood urea nitrogen sensor and said creatinine sensor are disposed within said at least one sample chamber.

9. The method of claim 5 wherein said obtaining step further includes obtaining a base layer having a plurality of electrically conductive paths on one side of said base layer, creating a blood urea nitrogen electrode, creating a creatinine electrode, creating a creatine electrode, and creating a reference electrode wherein said blood urea nitrogen electrode, said creatinine electrode, said creatine electrode and said reference electrode are disposed within said at least one sample chamber.