Sugar Coating

The A1C test is a blood test that reports levels of sugar in the blood over a two to three month period. Blood hemoglobin has a memory for this.
Hemoglobin in a protein in red blood cells. Sugar in the blood will coat some of the hemoglobin cells. The A1C measures the percentage of hemoglobin cells with the sugar coating. An A1C of 5 means 5% of the cells are coated, and A1C at 15% (not desirable) means 15% are coated.
The numbering can be confusing because home testing of blood sugars work with numbers usually ranging from 100 to 600. Home monitors and A1C tests are measuring very different things. The home test tells you were you are at that moment while A1C gives an average. For being an average, the A1C can be skewed by temporary but extreme highs and lows in daily blood sugar levels.
High A1C from a "non-diabetic" can be the basis of a diabetes diagnosis. The diagnosis will probably be right. Attention to your own behavior and self honesty is important. If an A1C is run in January, it will almost invariably be higher from holiday indulgences. One week of an ice cream binge will prompt higher A1C for up to three months, even if the home monitoring shows that blood sugar levels returned to normal the week after.
A diabetic can run with the 100-140 "healthy range" most of every day, but spike in the middle of the night or after one specific meal every ay. This will inflate the A1C level. Once the hemoglobin is sugar-coated, it stays that way for its two- to three-month lifespan.
The only way to tell where are problem times of day is to self test via home pricking. Both forms of testing are recommended and neither can truly replace the other.
There are different forms of testing A1C that use different number scales. It is standardized here in the United States.
Different diabetes organizations recommend different target numbers. 6.5 was once the norm. The American Diabetes Association raised the target to 7.0 because the lower levels did not reduce risks enough to compensate for the risks brought on by hypoglycemic (low blood sugar) episodes. I know personally of one healthy person diagnosed with "pre-diabetes" at a level just under 6.0% A1C. My cynical thought is that his doctor is doing his best to earn a golf trip offered by the pharmaceuticals for prescription quotas.
Here’s an interesting study from http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(09)61969-3/fulltext:  "A retrospective study of 47,970 diabetics found that [Type 2] patients with an A1C less than 6.5% had an increased mortality rate." Yes, that’s increased death for keeping the sugar too low. Things like that reaffirm my belief that being too good is not desirable. My theory is that constantly low numbers contribute to "fragile" diabetes. But I am no doctor and only have my own experiences to judge by.