Case 40: Diagnostic Testing

Case 40 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 her baseline, 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 2.4 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
Excellent! BK nephropathy is an important cause of acute kidney injury in the allograft, especially during the 1 year post-transplantation. The BK viral load is undetectable.
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 2.1 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
This patient does not have symptoms suggestive of a urinary tract infection and the urinalysis does not reveal pyuria.
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%.
Though CMV nephropathy is possible, this maybe a higher yield test pending other initial studies. This patient is CMV seropositive and received a CMV seronegative allograft, representing a relatively low risk for CMV infection.
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 IgA nephropathy
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 40 Index
Case 40 Introduction
Case 40 Physical Exam