Case 45: Diagnostic Testing

Case 45 Index

Take a look  this patient’s basic metabolic panel and urine studies:



Basic Lab Ref

Which of the following are the highest yield tests to perform next?
Genetic testing
You’re on the right track, but hold that thought!  Though genetic testing may confirm the suspected diagnosis, there are less expensive tests that may narrow down differential first.
Laxative screen
Try again! The studies above are not consistent with laxative abuse.
Plasma renin activity (PRA)
Though PRA may be a helpful test for some patients with metabolic alkalosis, the absence of hypertension makes this a lower yield test here.
Spot urine calcium:creatinine ratio  (Ca:Cr)
Nailed it! Here, the spot Ca:Cr is <0.2 mmol/mmol (<0.07 mg/mg).
Urine diuretic screen
This is a reasonable test given the clinical presentation and data provided this far. The urine diuretic screen is negative.
Dexamethasone suppression test
This test is helpful if suspicion is high for Cushing’s syndrome – thus far, we haven’t seen clinical evidence of this (e.g. hypertension, hyperglycemia, striae)
It’s decision time. What’s your diagnosis? Choose 1!
Diuretic abuse
Laxative abuse
Cushing’s syndrome
Bartter syndrome
Gitelman syndrome
Primary hyperaldosteronism
Surreptitious vomiting
Liddle syndrome
Proton-pump inhibitor side effect

Confident in your diagnosis? Let’s wrap up this case.

Click here to move on!

Case 45 Index
Case 45 Introduction
Case 45 Physical Exam