Laboratory tests seek to answer questions raised by clinicians after talking with and examining the patient. Laboratory tests can be used directly to confirm diagnoses, monitor a condition over time or monitor treatment. They can provide information about a person’s general health such as illnesses or abnormalities in organs of the body, for example the kidneys or liver. Laboratory tests can sometimes be used to ascertain if a treatment is effective or determine the presence of any potentially harmful side-effects.
Laboratory tests are usually carried out on biological samples such as blood (serum or plasma), dried blood spots on a card, saliva, faeces, tissue biopsies and urine collections. The type of sample will depend on what is being measured and the age and gender of the patient. Once a sample is taken, it is sent to the laboratories where scientists use a number of chemical and biological tests to measure the chemicals, in endocrinology these chemicals are usually hormones.
Hormone levels in a healthy person can vary according to a number of factors including time of day, food, drink, rest, stress, exercise and the menstrual cycle. These naturally occurring fluctuations make it difficult to interpret a single measurement of hormone levels especially when trying to distinguish between what is a normal and an abnormal result. Sometimes dynamic tests are required, where two or more samples are taken over a set time period, which allows scientists to account for these fluctuations such as glucose levels, fluid intake, certain drugs and exercise etc. Dynamic testing allows for a wider assessment of hormone levels during the sampling time. Dynamic tests can be used to test for hormone deficiency, where the test stimulates the hormone producing gland under investigation. Alternatively, when hormone excess is being investigated, the aim of the dynamic test is usually to try and suppress the hormone producing gland that is suspected of making too much hormone.
The clinical team will advise the patient on how to prepare for the test with specific information beforehand. Some tests require certain medications to either be given or withheld beforehand whilst other tests are best done during a fasting period – where the patient has abstained from some or all foods and drink for a set period of time.
The exact information may differ slightly from clinic to clinic but usually the clinical team will provide the patient with a test request form to take to the appointment. On this form, a patient’s name, date of birth, hospital number are essential. If samples (for example urine or faeces) are brought in by the patient, it is very important that the date and time that the sample was collected is stated clearly on the container.
Most samples can be taken at a general practitioner’s surgery or community clinic where tests are done. However, some hormone tests need to be processed quickly and the clinical team will usually advise these tests are taken in a specialist clinic or hospital where the laboratory team are on site. The clinical team usually discuss where and when the test should be taken.
Dynamic tests are more detailed and usually involve resting in bed while blood samples are taken over a period of time. Most dynamic tests do not require an overnight stay but if this is needed, the clinical team will provide details. It is imperative that patients attend with their medicines, inform the clinical team about any recent changes to their health and prepare as have been instructed to ensure the test results can be interpreted accurately.
Any queries about the details of individual tests should be discussed with the patient’s clinical team.
The blood level of several hormones changes significantly with the time of day. For example, cortisol is highest in the early morning and lowest late at night. This affects the time these tests can be conducted, for example, a test that stimulates the adrenal gland to test its function is best done in the morning. Conversely, when testing if the adrenal glands are producing too much cortisol, the clinical team might ask the patient to provide a salivary sample at midnight when the levels should be at their lowest.
The day (stage or phase) of the menstrual cycle also has a major impact on hormone levels. The timing of the sample during the menstrual cycle depends on the clinical question being asked. In general, blood samples taken in the ‘first half’ of the cycle (called the follicular phase) are used to assess abnormal hormone levels. However, progesterone is deliberately measured on day 21 in the middle of the ‘second half’ (called the luteal phase) to see if ovulation has occurred.
A reference range is the range of results seen in the general population, without the condition under investigation, taken under the same conditions as the patient e.g., a rested, fasted, non-pregnant female at 9am. There are ranges for different genders, ages, ethnicities, stages of the menstrual cycle, menopause and pregnancy. In any reference range there is a distribution of values; think of the heights of children in a classroom, most of the children will be within a 20cm range, however there will also be a few smaller and taller children, these would be classed as outliers. Therefore, the reference range includes most results seen in normal people, but not all of them (the extreme ones/outliers). This is important to understand as the reference range is a guide and not a rigid definition of health.
Similarly, the range of hormone levels in healthy people and those with illnesses sometimes overlap, making diagnosis difficult. Each laboratory test will be assessed to see how good it is at diagnosing a condition. The best laboratory tests are sensitive (clearly detect disease) and specific (do not provide a false diagnosis).
Samples of urine, saliva, faeces and finger-prick blood are currently used by the NHS for specific tests which have been developed within the laboratory using strict guidelines to provide the best results for the patient.
To provide a thorough and accurate diagnosis it is recommended that all tests are overseen by the patient’s GP and/or an endocrinologist. It is important that a doctor has carried out a full examination of the patient and talked to them face-to-face to ensure that they can properly interpret the results of any tests. The advantage of a professionally collected sample (by the patient’s GP or an endocrinologist), e.g., blood from a vein, is that the sample is collected appropriately and enough is taken to allow for repeated analysis without the delay and discomfort of taking another sample.
NHS laboratories undergo rigorous internal and external quality assurance checks to ensure that the results provided are of a high standard. This provides further reassurance about the result. With companies external to the NHS, such as those advertised online, there is no requirement to adhere to any internal or external quality assurance schemes. Before sending anything to an internet-based company it is important to investigate the standard of the tests provided.
When sending samples directly from home the quality of the sample may be reduced. As mentioned above there are lots of factors which can affect the test such as time, stress, diet or medication etc. In addition, with hormones, it is often best to measure more than one hormone at once in order to get the ‘full-picture’ and isolated measures of specific hormones can be misleading.
It can be difficult for internet laboratories without full knowledge of individual medical details, for example, the drugs being taken, to appreciate the significance of the results, or fully interpret them. It is important to take care when comparing results from different laboratories because significant variation can arise from differences in the measurement technology and methods.
Results are returned to the clinical team looking after the patient. The results may be discussed by a clinical team comprising of doctors, nurses and scientists who combine them with physical signs and symptoms to provide a holistic interpretation of the results. The patient may be contacted immediately to discuss the results or wait until they are next seen in clinic.
Results must be interpreted in the context of other medical details. With endocrinology in particular, the same numerical result may signify health in one person, but a problem in another. Patients should discuss results with their clinical team rather than trying to interpret them themselves.
Most routine tests are processed as soon as possible however the length of time for the result to be available can vary from test to test (days-weeks). It is important that patients ask their clinical team when to expect results.
Routine results are produced within one working day providing additional measurements are not required, for example, if it has to be double-checked. Results on samples sent to reference laboratories for special tests may take one to four weeks to return.
Last reviewed: May 2022
