Diabetes Insipidus is a disorder of less common incidence which develops either due to a marked deficiency of Vasopressin (the anti-diuretic hormone which has the sole role of dealing with maintenance of water balance), attenuation in the degree of response towards it by the kidneys or an excessively high intake of fluid.
There have also been a few cases in which diabetes insipidus occurs during the time of pregnancy. In short, diabetes insipidus can take up any of the following four forms- Central or cranial diabetes insipidus, Gestational diabetes insipidus, Nephrogenic diabetes insipidus or Dipsogenic diabetes insipidus.
Disruption in the formation, storage or secretion of anti-diuretic hormone (ADH) may take place due any of the following reasons- presence of tumour, infections such as encephalitis, inflammation of the meninges, head trauma or even surgery. Other than that, structural defects or deformities in the renal tubules also impair the ability of kidneys to respond to the action of vasopressin; for example, long standing kidney ailments, genetic disorders or medications, like tetracycline can be responsible for nephrogenic type of diabetes insipidus.
One of the hallmark signs of this condition is excessive urination or polyuria, so much so that the patient is unable to have an undisturbed sleep at night, and sometimes leads to bed wetting too. Some of the other classical symptoms include increased thirst or polydipsia, dry mouth, muscle cramps etc. Below given content discusses the various diagnostic tests that aid in confirming the presence or absence of this particular condition. An accurate diagnosis is essential as the treatment plan varies in accordance with type of diabetes insipidus.
Commonly Used Tests for Diabetes Insipidus
Analysis of Urine Sample
If lately you have been dealing with any of the above mentioned symptoms, especially in the frequency and amount of urination (more in the night), your doctor may suggest you to opt for urinalysis. This is a simple test which provides relevant clinical information on the physical appearance as well as chemical composition of urine, specifically, the level of concentration. In case you are undergoing other screening tests for the same condition at the same time, you might need to fast for a specific duration of time. Your doctor is the best person to advise you in that regard.
There are a few number of drugs which may affect the accuracy of this diagnostic test and results. Therefore, you must inform your doctor about the prescription and non- prescription medicines you are currently taking. If you are suffering from diabetes insipidus, the concentration of your urine will be low. In other words, the amount of water content will be on the higher side whereas the level of electrolytes and other waste materials will be considerably low. Also, the decrease in the amount of particles results in a lower than normal reading of specific gravity.
Water Deprivation Test
Unlike urinalysis, Water deprivation test will help in ascertaining the reason behind diabetes insipidus. This type of a test follows the given protocol in majority of cases. You will be asked to stop any liquid intake for certain amount of time (two to three hours or sometimes overnight) in order to evaluate as to how your system reacts in terms of change in body weight, output and composition of urine. If you are dealing with diabetes insipidus, your body will continue to excrete increased amounts of less concentrated urine.
However, if you do not have this condition and your system is working fine, the amount of urine being excreted will gradually decrease (as water intake has been stopped). Also, the urine will be more concentrated.
While the test is being conducted, the urine production is closely measured. Your doctor may also want you to undergo a blood test that allows them to gauge the level of anti-diuretic hormone during the phase of fluid deprivation. In case of small children and expectant mothers, this test is carried out under careful and close medical supervision so as to ensure that the total body weight does not drop by more than 5% during the test.
Once the water deprivation test has been done, the patient may be administered with an injection that contains a small amount of anti-diuretic hormone. This type of a test (also known as Vaspressin test) depicts how the patient’s body reacts to the presence of the injected hormone. This, in turn, aids in identification of the type of diabetes insipidus the patient has.
If, after the dose of vasopressin, the individual in concern stop producing and passing urine, it can be confirmed that the condition is linked to dearth of anti-diuretic hormone and a diagnosis of cranial or central diabetes insipidus is reached. On the other hand, if the patient still continues to excrete urine (after the injection), it can be inferred that the body has sufficient amount of anti-diuretic hormone but the excretory organs, that is, the kidneys are failing to respond to its presence. In such cases, it can be concluded that he or she has Nephrogenic diabetes insipidus.
A blood sample may be drawn to evaluate the level of electrolytes, namely sodium and potassium in the bloodstream. In case of diabetes insipidus, the value of both rises above the normal range.
Hypertonic Saline Infusion Test
To perform this diagnostic test, the patient is given an infusion of hypertonic saline solution (which consists of both salt and water). Following this infusion, a blood sample is drawn. Using this, the osmolality and level of anti-diuretic hormone is measured.
Magnetic Resonance Imaging
Your doctor may ask you to undergo another non-invasive, diagnostic procedure called Magnetic resonance imaging. The aim of this procedure is to be able to locate any structural abnormalities involving the pituitary gland or hypothalamus. In MRI of the body or head, a powerful magnetic field is utilized in combination with radio waves so as to visualize detailed images of the tissues. In case your condition is closely associated with a cancerous growth, immediate attention needs to be directed towards treatment of the tumour prior to management of diabetes insipidus.
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