Laboratory
There are various laboratory values and urine parameters that allow a differential diagnosis between a diabtes insipitus renalis or a diabetes insipitus centralis and other urinary concentration disorders. The main symptoms are a decreased sodium concentration and a reduced osmolality of the urine. This is due to the increased excretion of water and thus a reduced concentration of sodium in the urine.
In the blood or in the serum taken from a diabetic insipidus centralis patient, there is a lower concentration of ADH (antidiuretic hormone), as this is no longer released properly. In the case of diabetes insipitdus renalis this concentration is the same as in a healthy person. This is also an important distinction between the two forms of diabetes insipidus. In both classifications, the sodium concentration in the serum is higher and osmolality is higher. This can be explained by the reduced excretion of sodium in the urine.
Guidelines
The guidelines for diabetes insipidus neurohormonalis (i.e. diabetes insipidus centralis) include definition and basic information on the disease as well as diagnostic and therapeutic options. According to the guidelines, the diagnosis includes confirmation of polyuria (pathologically increased urine excretion) by a 24-hour urine collection. Further provisions include: A thirst test as the next diagnostic step is recommended in cases of low urinary osmolarity and simultaneously elevated or highly normal serum osmolarity.
A DDAVP test (also desmopressin test) can distinguish between central and renal diabetes insipidus. Depending on the initial situation and results, further imaging diagnostics (cMRI) may be recommended. Various other diagnostic options can also be recommended.
The guidelines also provide an evaluation of the results and further subsequent options. If the sodium and chloride concentration as well as the serum osmolarity is increased while the specific gravity or the osmolarity of the urine is decreased, the suspicion of diabetes insipidus is confirmed. The diagnosis can be further confirmed by the fact that the urine has a lack of concentration capacity with a simultaneous increase in sodium and serum osmolarity in the thirst test.
Similarly, the diagnosis can be supported by increased sodium and serum osmolarity values with simultaneously low ADH values. To differentiate between central and renal diabetes insipidus, the DDAVP test is used according to the guidelines. According to the guidelines, diabetes insipidus centralis can be excluded directly if normal serum electrolytes and normal serum osmolarity are present in the thirst test with an existing concentration capacity.
The guidelines also provide therapy recommendations: Medically, desmopressin is the drug of choice because it is an analogue of the missing ADH (antidiuretic hormone). It can be administered nasally (by nasal spray), enteral (via oral administration) or parenterally (intravenously). Dosage recommendations vary depending on the method of administration and the individual.
It is generally recommended to start with a low dosage, which can be adjusted upwards in the course of time. Surgically, according to the guidelines, the removal of a tumour, which may be the cause of the disease, may be recommended. – the serum and urine emolarity
- The serum creatinine and
- Urea concentration
- The measurement of the blood sugar level and possibly
- One ADH and one ßHCG measurement in serum.
