OUR resident Dr Zak has taken on questions from two readers with concerns about their recent blood tests.

Thank you to the two readers who wrote in this week requesting answers to queries regarding their blood test results. My advice is given in good faith and in line with current agreed practice and guidelines. However, it cannot be a substitute for consulting your own doctor.

I was told I had “borderline hypothyroidism” and offered either to have treatment or get my blood tests repeated in three months. I’m not sure what to do. Nicole, 32

Dr Zak says: Thyroid bloods tests are a commonly requested investigation. They are often done as part of a work up or monitoring of a particular condition, for example diabetes or heart disease.

Often, they are requested if a person complains of fatigue or weight gain.

The pituitary gland, located in the brain, produces thyroid stimulating hormone (TSH). As the name suggests, this stimulates the thyroid gland to produce the active hormone, thyroxine, which is involved in metabolism.

When enough thyroxine is produced, the pituitary recognises this and TSH levels are lower.

If TSH levels are above the normal range and thyroxine (T4) levels are at the lower end normal this is known as subclinical hypothyroidism.

The pituitary thinks that the thyroid needs to produce more of the active hormone, so secretes more TSH to stimulate this.

Some will go on from subclinical hypothyroidism to develop actual hypothyroidism, where the levels of T4 are below normal and levels of TSH are higher than the top of the range.

Doctors may choose to observe subclinical hypothyroidism initially. If you complain of symptoms of hypothyroidism, they may offer a trial of treatment straight away to see if this improves your condition and blood test results.

It is important to say that fatigue is a complex complaint. It has both physical and psychological causes, which sometimes exist together. A trial of treatment may not automatically make you feeling better.

I recently had my NHS health check bloods done and was very surprised to be informed that I may have chronic kidney disease and that the test would need to be repeated. The last time I had them done was before the pandemic, and as far as I am aware, there were no issues. I am 67 but have always considered myself fit and healthy. Don, 67

GFR or glomerular filtration rate is a measure of kidney function. Numbers above 90 are generally not recorded. Numbers less than 60 usually prompt further investigations, especially if this is the first time the GFR has dropped below 60.

You cannot make a diagnosis of chronic kidney disease (CKD) on one blood test. Kidney function, also referred to as renal function, is influenced by many factors. Perhaps one of the commonest reasons for a lower number is having not drunk enough water on the day of the test. It would perhaps surprise you that this can have a significant effect on the figures, even in those with healthy kidneys.

As you mention, the first thing to be done is to repeat the test, to see if this is a true figure, or a one-off, especially if your previous tests were normal. Kidney function does decline with age, and if you have not had a test for some time, this may be a reflection of age-related reduction.

Your doctor may also ask you to submit an early morning urine specimen, usually the first of the day, to check if there is any protein in it. Healthy kidneys do not normally leak protein into the urine, apart from in very small amounts.

If your second kidney function test comes back at over 60, then it is likely that you do not have anything to worry about and a yearly check should be sufficient.

If it returns as abnormal, then your doctor will look for risk factors for kidney disease, such as diabetes and high blood pressure, and manage these appropriately. In this instance your kidney function may be monitored more regularly, at least initially.

There are many lifestyle choices you can make to help prevent kidney disease. These include regular exercise, drinking enough water, not smoking, a low salt diet, and only consuming alcohol in moderation, if at all.

Certain drugs may damage your kidneys, including the regular or prolonged use of oral non-steroidal anti-inflammatory drugs, such as ibuprofen.