Dynamic Tests

The diagnosis and treatment of endocrine diseases are guided by laboratory tests to a greater extent than for most specialties. Many diseases are investigated through excitation/stimulation or inhibition/suppression testing. This might involve injection with a stimulating agent to test the function of an endocrine organ. Blood is then sampled to assess the changes of the relevant hormones or metabolites.

Common Dynamic Tests done in our Endocrine Center are as follows:

Short Synacthen Test

This test is generally done to test the steroid (Cortisol) axis in patients who are suspected to have adrenal insufficiency or to test the intactness of the hypothalamo-pituitary axis. The test is commonly performed at 8.00 am but can be performed at any time of the day. Synacthen is administrated intramuscularly and blood samples for cortisol are taken before the injection, 30 and 60 minutes after. The patient is non-fasting unless ACTH or other hormonal samples are needed with the test. Under aseptic precautions an intravenous cannula is inserted into a suitable vein and IM injection of Synacthen is given and follow-up samples are taken using the same cannulae at 30 and 60 mins. The test takes approximately 90 minutes and you will be able to go home. Please check with our staff as in most cases the results will be ready soon after and you will be able to consult the doctor on the same morning.

Oral Glucose tolerance test

For the diagnosis of Diabetes Mellitus
The patient should be on a normal diet without carbohydrate restriction for at least two weeks prior to the test. He or she should be fasted for 8-10 hours prior to the test. During the test he must remain seated and should not smoke. The glucose must be given in a volume of approximately 500mls of water over 5 minutes. Blood samples are taken at 30 or 60 mins intervals for 2-3 hours. Results will be immediately ready after your glucose tolerance test.

For the diagnosis of Acromegaly
The patient should be fasted from 9pm the night before. Basal samples are taken after forearm vein cannulation for growth hormone and glucose levels. 75 g glucose is administered over 5 minutes and samples are taken at 30 minute intervals for 2 hours. Failure of suppression of Growth hormone secretion occurs in acromegaly and your doctor will be able to infer your diagnosis from other tests and your clinical symptoms.

Clonidine stimulation test

This test is indicated in suspected growth hormone (GH) deficiency in children and is safer than insulin - induced hypoglycemia test. An inadequate response is seen in GH deficiency, either as an isolate state or as part of pan-hypopituitarism. Patient should be fasted for at least 8 hours before commencing test. The patient should be recumbent in bed and at complete physical and mental rest throughout the test. Under aseptic precautions an intravenous cannula is inserted into a suitable vein and secured with an IV dressing. Clonidine is administered orally as appropriate for the patient’s body surface area. Further blood samples at taken at 30, 60, 90, 120 and 150 minutes after Clonidine. All samples with sequence numbers and actual time taken will be documented and sent to the lab. After the test, because of the risk of hypotension, continuing bed rest for 3 hours is essential.

HCG Stimulation test

This test is done to check if testicular tissue is present and functioning and to assess the nature of Hypogonadism. HCG is injected intramuscularly at 9 am on days 0 and 3. Blood samples are obtained for testosterone measurement before each injection and 48 hours after the second injection. In hypogonadism, a failure of testosterone to rise after HCG suggests the absence of functioning testicular tissue. Conversely, a rise shows that a testis is present, which may be intra-abdominal if none is palpable in the scrotum. In gonadotrophin deficiency, without primary testicular abnormality, the low basal testosterone value should triple after HCG administration.

GnRH stimulation test (also known as LHRH test)

This test is done to investigate possible gonadotrophin deficiency or confirmation of precocious puberty. In a normally cycling female the test is not usually required, but if performed it should be carried out in the follicular phase of the menstrual cycle. The normal peaks can occur at either 30 or 60 minutes. An inadequate response may be an early indication of hypopituitarism. Pre-pubertal children should not have any response of LH or FSH to LHRH. If sex steroids are present (i.e. the patient is undergoing precocious puberty), the pituitary will be primed and will therefore respond to LHRH.

Water deprivation - DDAVP Test

This test is done to check the function of your posterior pituitary gland in cases of suspected Diabetes Insipidus. Patient is allowed clear fluids (water) at libitum overnight prior to test. Patient is also allowed light breakfast but no tea, coffee, alcohol or smoking. Normal anterior pituitary hormone replacement therapy (Hydrocortisone and Thyroxine) should be taken as prescribed, if necessary.

After IV cannulation, basal samples will be taken with starting of urine collections as appropriate. A thirst visual analogue scale will be continued throughout the test. Patient will not be allowed to drink any fluids for up to 8 hours. If hungry, Patient allowed dry biscuits only, but to fast preferably. The subject will be weighed every 2 hours. If there is more than 5% weight loss, or patient is ill, test will be stopped. Every 2 hours blood will be drawn for plasma osmolality, urine volume recorded and sample for urine osmolality retained. Patient will be observed throughout test (to avoid surreptitious drinking) and must not smoke.

At end of test (after 8 hours fluid deprivation or 5% weight loss) samples will be taken and then Desmopressin will be administered. Patients are allowed to eat and drink but fluid intake must be restricted to no more then total volume of urine passed during test +2 litres, over the next 12-16 hours.

Clomiphene test

This test is done to confirm suspected gonadotrophin deficiency. It is done to differentiate gonadotrophin deficiency from weight related hypogonadism and idiopathic delayed puberty. Clomiphene acts as an anti-oestrogen centrally and as an oestrogen peripherally. The central anti-oestrogen effect induces a rise in LH and FSH. Clomiphene is administered orally in divided doses. Side-effects like peripheral flickering visual phenomena or central haloes can happen, which will disappear after ceasing to take clomiphene.Serum LH and FSH on days 0,4,7,10. Serum progesterone on day 21 in females. LH and FSH show a definite rise to outside the normal range or double their basal value. In women day 21 progesterone may confirm ovulation. Lack of LH and FSH response suggests gonadotrophin deficiency due to pituitary or hypothalamic disease. In females a normal response may be followed by menstruation.

Dexamethasone suppression test

These tests are done as a screening or a diagnostic test when Cushing’s syndrome is suspected. Dexamethasone suppresses pituitary ACTH output by the operation of negative feedback on the hypothalamus and pituitary. The single dose or low dose suppression test will usually distinguish between normal patient and those with Cushing’s syndrome.

Overnight dexamethasone suppression test:
This is a convenience out – patient method for screening of Cushing’s syndrome, particularly in obese women or in PCOD. Dexamethasone is administered at bedtime. At around 8 am the following morning plasma cortisol will be measured and expected to be suppressed. Lack of suppression indicates the need for further investigation.

Low dose dexamethasone suppression test:
This is a more refined test to differentiate between normal (but fail to suppress on the overnight dexamethasone suppression test) and abnormal individuals who may have Cushing’s disease. It is most important that the dexamethasone is taken at exactly the right time as prescribed. Dexamethasone must be given at 6 hour intervals over 48 hours. 24 hour urine collections should continue throughout the test as per your doctor’s advice. They will be analyzed for urinary free cortisols as appropriate. Prior to the test, blood samples for ACTH and cortisol will be taken at 9 am and may be at midnight on two occasions. Dexamethasone is administered 6th hourly for 48 hours.

High dose dexamethasone suppression test:
In theory high dose dexamathasone suppression for 48 hours will suppress the plasma and urinary cortisol by 50 % in patients who have hypothalamic or pituitary dependent Cushing’s disease. In patients with an adrenal tumor or ectopic ACTH production suppression will not be observed. The protocol is exactly similar as for the low dose test and it may follow consecutively.