Hemoglobin which has diagnostic value in diabetes mellitus?
Glycated haemoglobin provides an accurate and objective measure of glycaemic control over a period of weeks to months. In diabetes, the slow non-enzymatic covalent attachment of glucose to haemoglobin (glycation) increases the amount in the HbA1 (HbA1c) fraction relative to non-glycated adult haemoglobin (HbA0). These fractions can be separated by chromatography; laboratories may report glycated haemoglobin as total glycated haemoglobin (GHb), HbA1 or HbA1c. In most countries, HbA1c is the preferred measurement. 
Davidson Ed 23 Pg 726
HbA
HbF
HbA1
HbS