Case 15: Diagnostic Testing

Case 15 Index

Here are some basic labs:

Labs Case 15.png

Basic Lab Ref

Choose the highest-yield tests below!
Kidney transplant biopsy
Hm, let’s wait a minute. This patient’s kidney function appears to be near the post-transplantation nadir. We might be able to perform some less invasive testing before subjecting this patient to an allograft biopsy.
Urinalysis & urine protein:creatinine ratio
In a patient with stable kidney function and diarrhea, this test is not the highest yield for an initial test. Try again!
Urine culture
In a patient with stable kidney function and diarrhea, this test is not the highest yield for an initial test. Try again!
 Clostridium dificile toxin B PCR stool test
Excellent! Diarrhea in an immunocompromied patient should raise suspicion for C. dificile colitis. The PCR test is negative.
 Donor and recipient CMV status
Excellent! The donor and recipient’s CMV status can help us stratify the risk of CMV infection. Here, the donor’s CMV status is positive (CMV IgG +) while the recipient’s CMV status is CMV negative (CMV IgG -).
 Gastroenterology (GI) consultation for colonoscopy and colonic biopsies
You call your GI colleagues and they advise you to continue your workup before subjecting this patient to an invasive colonoscopy. Keep going!
PCR Stool tests for parasites and viruses
Excellent! Diarrhea in an immunocompromised patient should raise suspicion for a wide variety of pathogens. Viruses may include norovirus, sapovirus, astrovirus, adenovirus, and rotavirus. Parasites typically include Giardia lamblia, cryptosporidia, Cyclospora cayetanensis, Dientamoeba fragilis, Entamoeba histolytica and microsporidia.  The stool tests are negative.
What is the next best test (choose one)!
Serum BK virus PCR
BK viremia is typically asymptomatic. It may picked up on screening tests or in the setting of acute kidney injury and indicative of over immunosuppression. BK nephropathy can also present with pyuria and acute kidney injury.
Mycophenolate acid (MPA) trough level
Unfortunately, MPA trough levels do not correlate with adverse effects related to the drug. While diarrhea is a common adverse effect, this test will not help us distinguish between drug-related diarrhea and other etiologies.
Serum adenovirus virus PCR
Thus far, we haven’t seen any evidence of adenovirus infection. Adenovirus nephritis may present with hematuria and acute kidney injury.
Great choice, the combination of donor CMV IgG+ and a CMV IgG – recipient presents the highest risk for post-transplantation CMV infection. The serum CMV PCR is 1,237,082 IU/mL. Further, diarrhea in an immunocompromised patient should raise suspicion for CMV colitis.
It’s time to lock in your final diagnosis! Which of the following best explains this patient’s presentation?
Cytomegalovirus (CMV) infection
Adenovirus infection
Acute cellular rejection (ACR)
Antibody-mediated rejection (AMR)
Mycophenolate-mofetil induced diarrhea
Tacrolimus-induced diarrhea
Pneumocystis jiroveci pneumonia (PJP)
BK virus infection
Post-transplant lymphoproliferative disorder (PTLD)

Click here once you’re confident in your diagnosis!

Case 15 Index
Case 15 Introduction
Case 15 Physical Exam