Case 54: Diagnostic Testing

Case 54 Index

Take a look at some preliminary testing!
Basic labs
Transplant Kidney Ultrasound
Urine Microscopy


Basic Lab Ref

Choose the highest yield tests below (more than one choice may be correct)!
BK virus serum PCR level
Good thought! Transplant recipients are at risk for opportunistic infections, and BK virus can cause BK nephropathy resulting in AKI. This patient’s BK virus serum PCR is undetectable.
Excellent idea. Given this patient’s hyperkalemia, we should look for any ECG abnormalities that may require more urgent hyperkalemia treatment. ECG shows normal sinus rhythm with no peaked T waves or QRS prolongation. 
Blood gas
Great thinking, especially in the setting of an AKI with a low serum bicarbonate. Acidosis can induce elevated serum potassium due to cell shift as well as increased activity of the hydrogen/potassium exchanger in the collecting duct.  While either a venous or arterial blood gas (ABG) would be sufficient here, here’s the ABG: 7.40/35/95 (pH/PCO2/pO2) 
Kidney biopsy
Though this may be reasonable later depending on further work up to look for rejection or glomerular disease if the AKI does not improve, noninvasive tests may be able to help us a bit more first.
Tacrolimus level
You nailed it! Tacrolimus can certainly cause hyperkalemia, especially since this patient has poor oral intake and AKI. Her trough tacrolimus level is 20 ng/mL.
Urine culture
This patient’s history and urinalysis are not suggestive of a urinary tract infection. Pick again!
Mycophenolate mofetil level
Unfortunately, mycophenolate levels do not correlate with adverse effects related to the drug. In addition, while diarrhea is a common adverse effect, this patient’s AKI and hyperkalemia are likely from another cause.

What’s on your differential diagnosis for acute kidney injury (AKI) in this patient? Pick your top 3!
Non-steroidal anti-inflammatory drug (NSAID) induced injury
Volume depletion
Calcium channel blocker toxicity
Steroid toxicity
Trimethoprim-sulfamethoxazole nephrotoxicity
Calcineurin inhibitor toxicity 
Obstructive nephropathy
Transplant renal artery stenosis (TRAS) 
Kidney Transplant Pyelonephritis
Rejection of pancreas allograft
Rejection of kidney allograft
Confident in your diagnosis? Click here to wrap this case up!

Case 54 Index
Case 54 Introduction
Case 54 Physical Exam