Early detection of diabetes

1. A method of diagnosing a subject as having or at risk of having pre-diabetes or diabetes, comprising:

a) obtaining a blood sample from the subject;

b) isolating erythrocytes having erythrocyte peptides from the blood sample, the erythrocyte peptides comprising at least one of the amino acid sequences selected from SEQ ID NOs: 1, 2, 3, 5, 7, 8, 15-17, 24, 26, 28-32 or 37, and optionally isolating the erythrocyte peptides having the selected amino acid sequences from the isolated erythrocytes;

c) performing an immunoassay to detect a level of O-linked N-acetyl-glucosamine (O-GlcNAc) modification of an amino acid residue within the amino acid sequence of at least one of the selected amino acid sequences of the erythrocyte peptides, the immunoassay comprising contacting the isolated erythrocytes or erythrocyte peptides with at least one first antibody that specifically binds to O-G 1 cNAc present on the amino acid residue of the at least one selected amino acid sequence of the erythrocyte peptides, wherein the at least one first antibody does not specifically bind other O-G 1 cNAc-modified peptides not having the at least one selected amino acid sequence, and with at least one second antibody that specifically binds the amino acid residue of the at least one selected amino acid sequence in a non-O-linked glycosylated state and detecting the first and second antibody bound to the O-G 1 cNAc-modified and non-O-glycosylated amino acid residue, respectively, of the at least one selected amino acid sequence; and

d) calculating a ratio of bound first antibody to bound second antibody and comparing the ratio to that of a corresponding normal sample, wherein if the ratio is different from the ratio of the corresponding normal sample a diagnosis of pre-diabetes or diabetes, or an increased risk therefore, is indicated for the subject.

2. The method of claim 1 , wherein the first or second antibody is detectably labeled.

3. The method of claim 1 , wherein the second antibody is a monoclonal antibody.

4. The method of claim 1 , wherein the second antibody is detectably labeled.

5. A method of monitoring a therapeutic regimen for treating a subject having or at risk of having hyperglycemia, comprising:

a) obtaining a blood sample from the subject;

b) isolating erythrocytes having erythrocyte peptides from the blood sample, the erythrocyte peptides comprising at least one of the amino acid sequences selected from SEQ ID Nos: 1, 2, 3, 5, 7, 8, 15-17, 24, 26, 28-32 or 37, and optionally isolating the erythrocyte peptides having the selected amino acid sequences from the isolated erythrocytes;

c) performing an immunoassay to detect a level of O-linked N-acetyl-glucosamine (O-GlcNAc) modification of an amino acid residue within the amino acid sequence of at least one of the selected amino acid sequences of the erythrocyte peptides, the immunoassay comprising contacting the isolated erythrocytes or erythrocyte proteins with at least one first antibody that specifically binds O-GlcNAc present on the amino acid residue of the at least one selected amino acid sequence of the erythrocyte peptides, wherein the at least one first antibody does not specifically bind other O-GlcNAc-modified peptides not having the at least one selected amino acid sequence, and with at least one second antibody that specifically binds the amino acid residue of the at least one selected amino acid sequence in a non-O-linked glycosylated state and detecting the first and second antibody bound to the O-GlcNAc-modified and non-O-glycosylated amino acid residue, respectively, of the at least one selected amino acid sequence;

d) calculating a ratio of bound first antibody to bound second antibody and comparing the ratio to that of a corresponding normal sample; and

e) administering insulin to the subject where the ratio is different from the ratio of the corresponding normal sample.

6. A kit comprising:

a) first container containing a first antibody that specifically binds O-linked N-acetyl-glucosamine (O-G 1 cNAc) present on an amino acid residue of a peptide, wherein the peptide is selected from SEQ ID NOs: 1-40 and wherein the first antibody does not specifically bind other O-G 1 cNAc-modified peptides not having the amino acid sequence of the selected peptide, and a second antibody that specifically binds the amino acid residue of the selected peptide in a non-O-linked glycosylated state; and

b) a second container containing a first detectably labeled reporter.

7. The kit of claim 6 , further comprising a second detectably labeled reporter.

8. A method of diagnosing a subject as having or at risk of having pre-diabetes or diabetes, comprising:

a) obtaining a blood sample from the subject;

b) isolating erythrocytes from the blood sample; and

c) performing an immunoassay to detect an increased level of β-N-acetylglucosaminidase (O-GlcNAcase) in the erythrocytes as compared to the level of O-GlcNAcase in a corresponding normal sample, wherein the immunoassay comprises contacting the erythrocytes with an antibody that binds O-G 1 cNAcase and detecting the bound antibody, wherein detection of the bound antibody is indicative of the level of O-G 1 cNAcase in the erythrocytes, and wherein an increased level of O-G 1 cNAcase as compared to that of the normal sample is indicative of the subject as having or at risk of having pre-diabetes or diabetes, thereby diagnosing the subject.

9. The method of claim 8 , wherein the antibody is a monoclonal antibody.

10. The method of claim 8 , wherein the antibody is detectably labeled.