Conventionally diabetes mellitus was diagnosed by high fasting or random blood glucose concentrations, or an abnormal oral glucose tolerance test (OGTT) whilst haemoglobin A1c (HbA1c) was used to monitor longer term glycaemic control in patients with known diabetes mellitus.

In 2011, the World Health Organisation (WHO 2011) recommended that HbA1c measurements should also be used to diagnose diabetes in the majority of asymptomatic individuals, and this recommendation has been agreed in the UK (NHS Diabetes 2011).

An HbA1c of 48 mmol/mol or more is consistent with diabetes. If the patient has no symptoms then a second HbA1c result must be obtained within 2 weeks, and if it remains ≥48 mmol/mol diabetes mellitus is confirmed.

HbA1c values of 42 to 47 mmol/mol suggest a high risk of future diabetes. Such individuals should be offered structured lifestyle education and support to delay/prevent development of diabetes, and have an annual HbA1c test.

HbA1c must be measured in an accredited laboratory undertaking recommended quality assurance procedures. Near patient testing is not appropriate when HbA1c is used for the diagnosis of diabetes.

HbA1c is now the preferred method to diagnose diabetes, except in the following situations where this test would be unreliable, and in whom the traditional methods of diagnosis with blood glucose concentrations remain the method of choice:

• Haemoglobinopathies
• Increased red cell turnover
• Anaemia (haemoglobin < 80 g/L)
• ?Type 1 diabetes or acute onset of symptoms of diabetes
• ?Gestational diabetes
• Children and adolescents
• Patients taking steroids and antipsychotic or other medications that cause a rapid rise in blood glucose

Despite this new approach, if an individual has abnormally high random or fasting blood glucose levels or abnormal OGTT, which would be consistent with diabetes on the traditional criteria, then that patient should be considered to have diabetes irrespective of their HbA1c value. Without symptoms of diabetes two abnormal tests of the same type (two high fasting/random blood glucoses or a diabetic OGTT) are required to confirm diabetes mellitus.

The laboratory will perform a screening test for immunoglobulin bound prolactin (macroprolactin) on samples with a prolactin greater than 600 mIU/L. Please contact the laboratory for further information.

The menopausal transition is best diagnosed on clinical grounds. Endocrine investigation may be helpful where the pattern of age, menstrual history and features of oestrogen deficiency are unusual.

Please indicate the woman’s date of birth, recent menstrual pattern and date of last menstrual period/day of cycle on which the blood sample was collected. A rise in follicle stimulating hormone (FSH) is the earliest sign of the approaching menopause. Measurement of serum FSH is the recommended first investigation if biochemical confirmation is necessary. The measurement of luteinising hormone (LH), oestradiol or progesterone is not appropriate. A serum FSH in the reference range for the follicular phase does not exclude the perimenopause.

Hormone Replacement Therapy

HRT when prescribed (orally or transdermally) for the relief of menopausal symptoms does not require endocrine monitoring. Where there is unexpected failure of treatment, for example due to non-compliance or malabsorption, investigation may be useful. Different formulations of HRT may or may not be detected by oestradiol assays. Please indicate on the request form the HRT preparation prescribed.

The main indication for measuring oestradiol in women on HRT is in those receiving implants containing oestradiol. Early replacement of the implant may result in accumulation of oestradiol. Monitoring of serum oestradiol before the implant is replaced has been recommended to avoid supraphysiological concentrations. Sometimes testosterone implants are used in HRT. Measurement of testosterone in an analogous fashion to oestradiol may help to assess whether a further implant may be necessary.

TSH and free thyroxine (fT4) are provided as first-line tests. Since many drugs and treatments affect thyroid function tests, details of all drugs or other treatment must be provided in order that further tests can be initiated by the laboratory as appropriate. Please indicate on request form if patient is on thyroid hormone replacement.

Free T3 is analysed only according to an agreed protocol and full clinical details must be given on the request form.

Thyroid hormone measurements can be misleading in patients with acute and non-thyroid illness. Thyroid status should only be assessed after recovery from acute non-thyroidal illness. 'Screening' of patients in hospital for thyroid illness is not recommended.

Please see the UK Guidelines for the Use of Thyroid Function Tests at: http://www.british-thyroid-association.org/current-bta-guidelines-