Case 30: Diagnostic Testing

Case 30 Index

A preliminary work-up is sent:
Head CT Scan

The patient’s head CT is normal without evidence of intracranial hemorrhage, extracerebral fluid collection, midline shift or mass effect. There is some artifact from patient motion.
Basic labs
The patient has no prior laboratory results for comparison.

protein BMP

As you go back to check on the patient, she has a 1 minute seizure. Her blood pressure just before the seizure is 155/85. What is the best next step in management?
Administer a 1L bolus of normal (0.9%) saline.
This patient is hemodynamically stable, and her seizure is most likely driven by her low serum sodium. Given the likely etiology, normal saline may actually worsen her hyponatremia here. Try again!
Administer a 50 – 100 mL bolus of hypertonic (3%) saline.
Correct! We need to rapidly correct this patient’s hyponatremia, as this is the most likely cause of her seizure. This bolus would be expected to raise her serum sodium by approximately 1-2mEq, hopefully enough to get her out of danger.
Administer a bolus load of levetiracetam (Keppra).
This patient’s seizure is likely due to an electrolyte abnormality which needs rapid correction. Try again!
Start a hypertonic (3%) saline drip at 10mL/h.
While this is an appropriate medication choice, this drip will likely not be enough to correct her electrolyte abnormality quickly. Try again!
Repeat a head CT scan.
While it may be helpful to repeat head imaging once the patient has stabilized, this is not the best first step. Try again!

The patient’s seizure resolves with your intervention and her mental status has improved.

Which of the following are the highest yield tests to determine the etiology of this patient’s hyponatremia?
Triglyceride levels
Elevated triglyceride levels and paraprotein levels can falsely elevate the sodium laboratory result if the indirect potentiometry is utilized. The patient’s symptomatic hyponatremia makes pseudohyponatremia less likely, making these tests less helpful here.
Urine sodium and urine osmolality
Excellent! More on these results below.
Serum osmolality
Good choice! The serum osmolality (drawn prior to administration of hypertonic saline) is 242 mosm/kg. 
Serum uric acid
Great! The uric acid level is below the lower limit of normal.
Glucose level
Hyperglycemia can lead to hypertonic hyponatremia. We already have a normal glucose value, making this etiology unlikely.
Methanol level
Though this patient seems to have ingested a substance, methanol is less likely given the absence of an anion gap metabolic acidosis.
Repeat laboratory tests and a few additional tests are sent:
Additional Laboratory Testing (drawn prior to administration of hypertonic saline)
Urine Osm 500

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

Case 30 Index
Case 30 Introduction
Case 30 Physical Exam