Case 39: Diagnostic Testing

Case 39 Index

Basic initial testing is performed.
Basic labs
Urine sediment
Urine sediment evaluation is bland, without cells or casts.
Ultrasound examination
The ultrasound shows kidneys of normal size without hydronephrosis or increased echogenicity.

Basic Lab Ref

What additional testing should be done next (more than 1 may be correct)?
Kidney duplex doppler ultrasonography
While this is a reasonable, non-invasive test for renal artery stenosis (as is spiral CT  with CT angiography), clinical suspicion here is lower with normal bilateral kidney size and the absence of other underlying vascular disease. There is a better test to perform first. If work-up is otherwise unrevealing or the patient fails to respond to medical therapy, this may be a good next step.
Plasma fractionated metanephrines and catecholamines
A good choice! This patient’s plasma levels of metanephrine, norepinephrine, epinephrine, and dopamine are within normal. You even grab a 24 hour urine which is normal as well, but your patient didn’t enjoy collecting it!
Plasma renin activity (PRA) and plasma aldosterone concentration (PAC)
Great choice! This patient’s PAC is 25 ng/dL (normal < 10ng/dL) and PRA is 0.5 ng/mL/hour (suppressed, < 1ng/mL/hour).
Anti-nuclear antibody (ANA)
We might send this test if we suspected a connective tissue disease (CTD), like systemic lupus erythematosus (SLE). This patient’s initial presentation does not suggest SLE or other CTD. Try again!
Sleep study
This patient’s STOP-BANG score (a screening questionnaire developed by Chung et al for obstructive sleep apnea, OSA) is 2, which makes him low risk for OSA. Pick again!
24 hour urine free cortisol
This is a good initial test for Cushing’s syndrome, with most recommendations suggesting 2 measurements. However, 24 hour urine collection is cumbersome and requires effective education and counseling, and late-night salivary cortisol (2 readings) may be preferred. This patient’s urine free cortisol level is normal.
24 hour urine potassium
This cumbersome 24 hour urine collection test may not be necessary in this case, try a different test first! If the patient is undergoing 24 hour urine testing for other reasons, however, urine potassium level could be sent. In this case, the patient’s 24 hour urine potassium is 55 mEq/day.

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Case 39 Index
Case 39 Introduction
Case 39 Physical Exam