**Core Concept**
Glycosylated haemoglobin (HbA1c) is a blood test that measures the average level of glucose in the blood over the past 2-3 months. It is a crucial marker for assessing glycaemic control in diabetic patients, helping clinicians to determine the effectiveness of treatment and make informed decisions.

**Why the Correct Answer is Right**
The American Diabetes Association recommends that the target HbA1c level for most adults with diabetes should be less than 7%. However, for patients with a history of severe hypoglycemia or those at increased risk of hypoglycemia, a target HbA1c of 7.5-8.5% may be more appropriate. The normal range of HbA1c for adequate glycaemic control in diabetic patients is generally considered to be between 6-8%. This range reflects good glycaemic control, which reduces the risk of microvascular complications such as diabetic retinopathy and nephropathy.

**Why Each Wrong Option is Incorrect**
**Option B:** An HbA1c level of 8-10% is considered poor glycaemic control, increasing the risk of microvascular complications.

**Option C:** An HbA1c level of 4-6% is lower than the normal range for most adults and may indicate hypoglycemia or other underlying conditions.

**Option D:** An HbA1c level of 10-12% is considered very poor glycaemic control, significantly increasing the risk of microvascular complications.

**Clinical Pearl / High-Yield Fact**
It's essential to note that HbA1c levels can be affected by factors such as hemoglobinopathies, blood transfusions, and certain medications, which may lead to inaccurate results. Clinicians should consider these factors when interpreting HbA1c levels and use them in conjunction with other markers of glycaemic control.

**✓ Correct Answer: A. 6% to 8 %**