How does a kidney transplant affect urinalysis parameters?
A: Urine analysis in the first 14 days post-kidney transplant is critical for determining the fate of the allograft. Understanding the challenges associated with each phase post-kidney transplant is therefore crucial for laboratorians.
As an example, take the case of a 58-year old man in our hospital who had a living donor kidney transplant after diagnosis with end-stage renal disease. His urine sample was sent to the laboratory for urine creatinine determination about an hour after the transplant. However, the lab was unaware of the transplant timeline. When staff found that his urine creatinine was below the detectable limit of our instrument, a technologist called our attention to the sample, and we reached out to the provider, who explained the patient’s situation. The next day, the patient’s urine creatinine rose to 36 mg/dL, and by the fourth day post-kidney transplant, his urine creatinine was within the normal range at 133 mg/dL, indicating that the allograft was healthy.
Similar to urine creatinine, proteinuria tends to fall significantly following a kidney transplant. If a rapid increase in proteinuria occurs, this suggests allograft pathology and is associated with graft failure. The leading causes of proteinuria post-kidney transplant are mammalian target inhibitors of rapamycin treatment, antibody-mediated rejection of the allograft, and toxic agents (Transpl Int 2012;25:909-17). It’s also important to note that proteinuria following a kidney transplant might be from the allograft or from the native kidney.
Besides the measurement of biochemical parameters, urine sediment analysis in the early phase post-kidney transplant is critical. Several studies have shown that a small quantity of renal tubular cells can be seen during post-transplant urine microscopy, especially in the first 2 weeks post-kidney transplant. Higher tubular cells in urine sediment post-kidney transplant are associated with acute kidney rejection.
Overall, an understanding of the sample collection timeline is critical for analyzing and interpreting urine samples following a kidney transplant, as is clear communication with providers. In particular, laboratorians should be familiar with the fact that the delay in organ function restoration may impact the content of urine post-transplant.
Following kidney transplants, do you recommend spot or 24-hour urine collection for urine protein and creatinine analysis?
There are no official recommendations on what urine sample type to use following kidney transplants. However, due to compliance and the problem of under- or over-collection of 24-hour urine, spot urine has been widely used to determine albumin or protein creatinine ratio (ACR/PCR).
Several studies have shown a good correlation between spot and 24-hour urine analysis of ACR/PCR following kidney transplants. Though other studies have demonstrated less correlation, it appears that the choice of method for urine creatinine analysis can contribute to the agreement between these two options (PLoS ONE 2016;11:e0166547). Specifically, an enzymatic method is more suitable for urine creatinine measurement following kidney transplant because of possible protein interference with the Jaffe method. Using an enzymatic method improves the correlation between spot and 24-hour ACR/PCR, while also enhancing the use of estimated glomerular filtration rate in establishing and monitoring kidney failure.
John O. Ogunbileje, PhD, is a clinical chemistry postdoctoral fellow at the University of Texas Medical Branch in Galveston, Texas. +Email: [email protected]