Case 29: Diagnostic Testing

Case 29 Index

In addition to the chemistry panel, additional labs are obtained:

all 29 labs

protein BMP

Choose the highest-yield tests that you would perform next!
Urinalysis and urine microscopy
Though this is an inexpensive, non-invasive test, in a patient with normal kidney function and hyponatremia, this is not the highest yield. Try again!
Orthostatic vital signs
Well done – orthostatics are a sensitive way to assess a patient’s volume status. This patient’s blood pressure and heart rate remain stable after changing from a sitting to standing position (and standing for 2-3 minutes), and he remains asymptomatic.
Urine protein: creatinine ratio
Though this test may be abnormal in a patient with multiple myeloma,  it is less likely to help us determine the etiology of the patient’s hyponatremia.  In a patient with normal kidney function and hyponatremia, this is not the highest yield initial test. Try again!
Urine osmolality
Excellent! Urine osmolality can help us better 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 (or ADH-dependent hyponatremia), while lower osmolality suggests lower activity of ADH (ADH-independent). This patient’s urine osmolality is 210 mOsm/kg.
Urine sodium
Excellent! Urine sodium can help us understand the effective circulating volume or effective arterial volume (EAV) along with aldosterone activity. This patient’s urine sodium is 90 meq/L.
Serum osmolality
Great! This test can help us get a better sense of our patient’s tonicity in the setting of hyponatremia. The serum osmolality is 285 mOsm/kg. (normal range: 275 – 295 mOsm/kg)

Click here once you’re confident in your final diagnosis!

Case 29 Index
Case 29 Introduction
Case 29 Physical Exam