THIS week, Dr Zak answers the questions of two readers who wrote in about their borderline blood results.

My advice is given in good faith, in accordance with current guidelines and practice. It cannot be a substitute for consulting your own doctor.

I have recently had my bloods as part of a routine health check. I was advised I had prediabetes. I am very worried as I know the problems diabetes can cause. Diane, 48

Dr Zak says: Blood sugars are measured in a few ways. They can be checked randomly, which can be either a fasting or non-fasting sample. The second way is by checking something called HbA1c, also known as glycosylated haemoglobin. Sugars are carried in haemoglobin, a molecule found in red blood cells (RBCs). The average lifespan of an RBC is three months. Hb A1c gives an indication of your blood sugars over the last three months.

This is often favoured over a random/fasting sample when making a diagnosis of diabetes, although both methods can be used. If a random/fasting sample shows a high reading, your Hb A1c may be checked to confirm the diagnosis.

However, in terms of health checks, usually just HbA1c is tested.

Normal readings are 26-41 mmol/mol and prediabetes is 42-47. A formal diagnosis of diabetes can be made if the HbA1c is 48 or above.

Prediabetes can be looked at in two ways. It can be seen as a precursor to the actual development of diabetes. Between 5-15% percent of those with prediabetes will become diabetic within 12 months.

Yet at the same time it may also be seen as a golden window of opportunity. Type 2 diabetes is increasingly being acknowledged as a lifestyle disease, or at least where lifestyle choices have a role in its development.

Weight loss, regular cardiovascular exercise, reducing alcohol consumption to within recommended limits and a healthy diet in combination are shown to help reduce borderline sugar levels to within normal readings.

However, these measures must be continued to avoid sugars rising, and the development of actual diabetes, which can have serious and devastating consequences.

I am always tired and I have struggled with my weight for as long as I can remember. I asked my GP for some blood tests. I was told that I have borderline hypothyroidism – Andy, 53

Dr Zak says: The thyroid gland is in the neck. It is controlled by the pituitary gland, located in the brain. Your thyroid gland secretes two active hormones, thyroxine (T4) containing four iodine atoms, and triiodothyronine (T3), this containing three. In the body T4 is converted to T3, the hormone that influences the rate of your metabolism.

If the pituitary senses low levels of T3 and T4 in the bloodstream, it increases production of thyroid stimulating hormone (TSH). As the name suggests, this aims to boost the production of T3 and T4.

When levels of these hormones are normal, TSH production reduces back to within normal limits. This has often been likened to the thermostatic control of the heating system in a house.

Hypothyroidism proper is when TSH is above the normal level, yet despite this T4 (the most measured active hormone) is below normal.

Subclinical hypothyroidism is when TSH is above normal, yet T4 is within the normal range. Often it is toward the bottom end of normal.

In these circumstances many doctors may wish to perform another blood test. This is for thyroid peroxidase (TPO) autoantibodies. These are autoantibodies which if present will attack the thyroid gland. In this case, progression to actual hypothyroidism is much more likely.

Your doctor may suggest either repeating the blood tests at a suitable interval, typically three to six months. Others may offer a trial of treatment with the medication levothyroxine.

It is important to address an underactive thyroid as if left untreated it will increase your risk of cardiovascular disease.

However, it must also be said that there are many causes of fatigue and weight gain. Though many people report an improvement in their symptoms after commencing medication, this is not always the case.

Many individuals who report symptoms which may be linked with an underactive thyroid have normal blood test results. Other blood tests are often done along with thyroid tests, for example to check for anaemia.

It is also important to be honest with yourself as to how much your lifestyle may be contributing to how you are feeling, and not feel upset if your results return as normal.