Question

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1. what does low serum complement C3/C4/CH50 indication in a lab test?

2. Why would kidney size decrease with renal artery stenosis?

3. why would we see increase Na and Cl in Diabetes Inspidus? Why would blood venous be alkaline?

4. why would a serum osmalilty be high be a urine osmalilty in diabetes inspidus??

5. What does the water deprivation test , test for? and how can we interpret its results?

Answer 1

Sodium is a very important component within your body. Its presence helps to regulate blood pressure levels. It also supports muscles, the central nervous system, and works to help support a healthy fluid balance. When someone is suffering from diabetes insipidus, one of the key indicators is that sodium levels within the blood will not be within normal values.

When sodium levels are too high, then this condition is called hypernatremia. If sodium levels are too low, then this condition is called hyponatremia. Although all laboratories have their own set of values they consider normal, healthy individuals typically have sodium levels that are 135-145 milliequivalents per liter [mEq/L]. Values above or below this normal level may lead to a sodium imbalance diagnosis.

Patients with NDI excrete > 50 mL/kg of urine/day (polyuria). If urine osmolality is < 300 mOsm/kg (water diuresis), central diabetes insipidus or NDI is likely. With NDI, urine osmolality is typically < 200 mOsm/kg despite clinical signs of hypovolemia (normally, urine osmolality is high in patients with hypovolemia).

The fluid deprivation test assesses the ability of the kidney to concentrate urine under the influence of ADH. Occasionally further investigations are required particularly when only partial forms of the condition are present.

The patient is allowed fluids overnight. The patient is deprived of fluids for 8 hours or until 5% of the body mass has been lost. The patient needs to be weighed hourly. Plasma osmolality is measured 4 hourly and urine volume and osmolality every 2 h. At the end of 8 h the patient is given 2 mcg of intramuscular desmopressin and urine and plasma osmolality checked over the next 4 h.

If serum osmolality rises to >305 mmol/kg the patient has diabetes insipidus and the test is stopped.

With cranial DI the urine osmolality remains below 300 osmols/kg and rises to >800 after desmopressin. With nephrogenetic diabetes insipidus the urine osmolality is <300 both before and after desmopressin.