Blood glucose monitoring provides an accurate indication of how the body is controlling glucose metabolism. It enables clinicians and patients to adjust their treatment accordingly to achieve optimal glucose control (Kreider et al. [99]). In the short term it can prevent hypoglycaemia and hyperglycaemia, and in the long term it can significantly reduce the risk of prolonged, life‐threatening vascular complications (NICE [134], Walden et al. [205]).

Capillary blood glucose monitoring provides immediate results and shows whether blood sugar is high or low, whereas urine testing indicates instances of high blood sugar and the presence of ketones (Adam et al. [2], Marini and Dries [112]).

Although capillary blood glucose monitoring is an essential part of diabetic management, it can have severe consequences if not done correctly; therefore, it is imperative that on initial diagnosis the individual is shown the correct basic technique (NICE [134]). In addition, appropriate healthcare staff should undergo formal training and any equipment used should be subjected to strict quality control (MHRA [117]).

Blood glucose monitoring needs to be performed regularly enough for patterns to be established on which treatment changes (e.g. to insulin regimes) can be based (Phillips [162]). What constitutes ‘regularly’ will vary in different circumstances; for example, illness, change of daily routine and hospitalization may affect diabetes control and therefore require more frequent testing (Walden et al. [205]). Generally, people with type 1 diabetes will need to test their blood glucose several times a day or more depending on their treatment regime, while those with type 2 diabetes will require less testing due to the lower risk of large fluctuations in blood glucose levels (Meetoo et al. [114]). There is variation in the literature surrounding the frequency of blood glucose monitoring for type 2 diabetes; however, for patients with type 1 diabetes it is suggested that monitoring four or more times daily is a minimal requirement, with measurement being imperative on waking and prior to going to bed (NICE [128]). Closer monitoring has been proven to have a positive impact on the control of blood glucose levels (Elgart et al. [58]).

Testing regularly will permit the individual to be aware of their blood sugar levels, allowing them to have better control and thus better stabilize their glycaemic variability. This will in turn reduce the likelihood of long‐term complications, in particular vascular complications such as retinopathy, nephropathy and cardiac autonomic neuropathy (Virk et al. [204]).

Blood glucose monitoring should be individualized depending on the type of treatment (diet versus oral medication versus insulin), level of haemoglobin A1c (HbA1c) (see below for further information) and treatment goals (WHO [214]). These should be evaluated frequently and reassessed with the support of a healthcare professional (NICE [128]). HbA1c measurement provides information relevant to overall glucose control as it measures the amount of glucose surrounding a haemoglobin molecule (Peate and Bennet‐Long [156]); it is a vital component of overall diabetic control (NICE [136]). It is typically lower than 6% in a normal healthy person (NICE [128]). As the body's glucose levels increase, more haemoglobin becomes glycosylated (glucose binds with haemoglobin), and, in a person with diabetes, further glucose molecules attach to the haemoglobin molecules, which can remain for around 3 months – that is, the life of the blood cell (Marieb and Keller [111]). Guidelines suggest that diabetic patients should aim for an HbA1c of 6.5% or lower; however, individual targets may be given by the healthcare team depending on the individual and type of treatment (NICE [128]).

Within the hospital setting, self‐monitoring of blood glucose may be appropriate for competent adult patients who are medically stable and successfully self‐managing their diabetes at home (Mabrey and Setji [107]). This would need to be supported by local policy, adequate patient assessment and the necessary documentation.

Blood glucose testing involves obtaining a drop of capillary blood and adding it to a testing strip, which is then analysed by a blood glucose meter (Marini and Dries [112]). Previously, most glucometers offered the option of using blood from the palm of the hand or the side of the hand; however, it is now routinely recommended that blood is only used from fingertips as the blood from this area responds rapidly to changes in blood glucose level and provides more reliable results (NICE [128]). The fingertips contain nerve endings, which can become painful and less sensitive with frequent testing; therefore, the outer parts of the finger, the thumb and the forefinger should be used sparingly due to their continual use in apposition and because these tend to be more painful (Adam et al. [2]). It is important to rotate the areas used for blood glucose testing to avoid infection from multiple stabbings, to avoid areas becoming toughened and to reduce pain (Walden et al. [205]).

The patient will have their blood sugar levels kept as near normal as possible via blood glucose testing and control (Meetoo et al. [114]). Trials have shown the benefits of tight glycaemic control at near normal levels, which resulted in reductions in length of hospital stay, sepsis, dialysis, and hospital mortality and morbidity (Preiser et al. [165], Wise [217]). Improved glycaemic control positively impacts patients’ quality of life and reduces the risk of further complications (Penning et al. [159]).