Case 20: Diagnostic Testing

Case 20 Index

You order routine basic labs which result once the patient has returned home from your clinic:

2018-10-28 (3)

Basic Lab Ref

Given this patient’s elevated creatinine from his baseline of 1.2 mg/dL, you advise the patient to come back to clinic the next day for expedited further work-up and management. You ensure he has had normal oral intake, and he reassures you that he has been eating and drinking normally.

In the clinic, you perform some additional diagnostic tests:
Urinalysis/microscopy, urine electrolytes
Transplant Ultrasound

You also send a repeat chemistry panel to ensure there was no lab error, and this patient’s creatinine is in fact high at 2.0 mg/dL. Based on these initial studies, it seems additional testing will be required.

Choose the highest-yield tests below (many of these will be helpful)!
Serum BK virus DNA PCR
BK viremia is typically asymptomatic, and may be the cause of acute kidney injury in transplant patients. Unfortunately, this test takes awhile to come back.
Allograft biopsy
Great! Acute kidney injury in kidney transplant recipients should be investigated with a biopsy if a reversible etiology is not found.
Mycophenolic acid (MPA) trough level
MPA trough levels do not correlate with adverse effects related to the drug. Try again!
Tacrolimus trough level
This patient’s morning tacrolimus trough level is 9.6 ng/mL.
 Donor specific antibodies (DSA)
Absolutely! Looking for the formation of de novo DSA (antibodies that form after transplantation) may raise our suspicion for antibody mediated rejection as an etiology of AKI.
Urine culture
Transplant urinary tract infection (UTI) or pyelonephritis can be a cause of acute kidney injury. This patient’s gram stain is negative and the urine culture shows no growth.
Urine eosinophils (Hansel’s stain)
 This test has a low sensitivity, and its positive predictive value for acute interstitial nephritis (AIN) is only about 40%.
The combination of donor CMV IgG+ and a CMV IgG – recipient presents the highest risk for post-transplantation CMV infection. Patients with CMV viremia are at risk for CMV infection of the allograft. The CMV PCR level here is undetectable.
Based on the information we have thus far, what are the top three diagnoses on your differential?
Cytomegalovirus (CMV) infection
Acute cellular rejection (ACR)
Antibody-mediated rejection (AMR)
Recurrent FSGS
Tacrolimus toxicity
BK virus nephropathy (BKVN)
Acute interstitial nephritis (AIN)
Post-transplant lymphoproliferative disorder (PTLD)
Hypertensive nephropathy
Obstructive uropathy

We need a kidney biopsy to make the diagnosis here! Click here to perform an allograft biopsy.

Case 20 Index
Case 20 Introduction
Case 20 Physical Exam