Case 13: Diagnostic Testing

Case 13 Index

Here are some basic labs:

Case10labs.png

Basic Lab Ref

Choose the highest-yield tests below!
Urinalysis/microscopy
In a patient with normal kidney function and hyponatremia, this test is not the highest yield for an initial test. Try again!
Orthostatic vital signs
Well done – orthostatics are a sensitive way to assess a patient’s volume status. This patient’s blood pressure drops to 100/60 with a HR of 90 upon standing (after standing for 2-3 minutes).
Urine protein: creatinine ratio
In a patient with normal kidney function and hyponatremia, this test is not the highest yield for an initial test. Try again!
Urine osmolality
Excellent! Urine osmolality can help us understand the etiology of a patient’s hyponatremia and tell us about the activity of the antidiuretic hormone (ADH). Higher osmolality suggests ADH activity is high, while lower osmolality suggests lower activity of ADH. This patient’s urine osmolality is 744 mOsm/kg.
Urine sodium
Excellent! Urine sodium can help us understand what the effective circulating volume or effective arterial volume (EAV) of a patient is. This patient’s urine sodium is 53 meq/L.
Urine sediment
In a patient with normal kidney function and hyponatremia, this is not the highest yield initial test.
Serum osmolality
Though psuedohyponatremia is not common, this test can help us ensure that our patient’s hyponatremia is true hyponatremia. The serum osmolality is 268 mOsm/kg. (normal range: 275 – 295 mOsm/kg)

 

It’s time to lock in your final diagnosis. What do you think is the most likely primary cause of this patient’s hyponatremia?
Cisplatin-induced salt wasting
Pseudohyponatremia
Syndrome of inappropriate antidiuretic hormone (SIADH) due to SSRI use
Hypovolemia
Low solute intake (tea & toast diet, beer potomania)
Glucocorticoid deficiency
Cyclophosphamide-induced SIADH
SIADH due to post-operative stress
Congestive heart failure
Cirrhosis

Click here once you’re confident in your diagnosis!

Case 13 Index
Case 13 Introduction
Case 13 Physical Exam