Case 1: This patient presented with thirst, polyuria and polydipsia. Studies sho
ID: 51003 • Letter: C
Question
Case 1:
This patient presented with thirst, polyuria and polydipsia. Studies show the following lab results:
Lab Measurement
Patient Results
Normal Range
Serum Glucose
100mg/dL
Serum Sodium
146mM
Serum BUN
22mg/dL
Hemoglobin
17.2g/dL
Hematocrit
51%
Urinary sodium
77mM/day
Serum creatinine
1.0mg/dL
Serum uric acid
Serum potassium
4.8mg/dL
Serum insulin
WNL
Plasma renin activity
Low
Plasma osmolality
308mOsm/kg
Urine osmolality
250mOsm/kg
Amanda R. is a 20-year-old junior in college. Beginning about a month ago, she noticed that she was waking up once, sometimes twice a night, to go to the bathroom. More recently she has noticed that she needs to go to the bathroom during her school day much more frequently than before, sometimes as often as once every hour.
Her mother insisted that she go see the family physician. No abnormalities were found on physical examination. Amanda had no history of traumatic head injury and an MRI of her brain was normal. Next, a 2-h water deprivation test was performed on Amanda. After two hours of not being able to drink water, the osmolarity of her plasma and urine was measured a second time. This time her urine osmolarity was unchanged but the osmolarity of the plasma increased to 315mOsm/kg.
Based on the results, explain the problem that Amanda is having.
Question 1
Describe the mechanisms by which normal fluid regulation in the body occurs?
Question 2
What is the possible treatment of this disease?
Question 3
What other conditions cause polyuria and polydipsia?
Please answer question 1,2,3 and explain
Lab Measurement
Patient Results
Normal Range
Serum Glucose
100mg/dL
Serum Sodium
146mM
Serum BUN
22mg/dL
Hemoglobin
17.2g/dL
Hematocrit
51%
Urinary sodium
77mM/day
Serum creatinine
1.0mg/dL
Serum uric acid
Serum potassium
4.8mg/dL
Serum insulin
WNL
Plasma renin activity
Low
Plasma osmolality
308mOsm/kg
Urine osmolality
250mOsm/kg
Explanation / Answer
1. Fluid level in the body is regulated by a Hormone called Anti Dieuretic Hormone (ADH). When the osmolarity of the blood increases (due to dehydration), release of ADH is stimulated. ADH in turn stimulates increased reabsorption and thus leads to concentrated urine. Due to overhydration vice versa happens. This way normol fluid regulation occurs in the body.
2. After the 2-h water deprivation test the plasma osmolarity is rightly higher. Under such circumstances if the kidney functions normally, it concentrates the urine to maintain the fluid level. But in the above case it is seen that the urine osmolarity is unchanged, indicating renal problem.
3. Polyuria and polydipsia are caused under following conditions :-
Diabetes milletus, central Diabetes Inspidus, due to chemical substances like diuretics, cffiene and ethanol.
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