Original Investigation
Transplantation
Effect of Clinical Variables and Immunosuppression on Serum Cystatin C and Beta-Trace Protein in Kidney Transplant Recipients

https://doi.org/10.1053/j.ajkd.2009.06.003Get rights and content

Background

Cystatin C and beta-trace protein (BTP) are low-molecular-weight proteins that have generated interest as alternative endogenous markers of glomerular filtration rate (GFR). Studies examining the effect of demographic, biometric, clinical, and biochemical variables on cystatin C levels have yielded conflicting results, perhaps because of the reliance on inferior methods of GFR determination. The aim of this study is to examine the independent effect of various clinical parameters on serum concentrations of creatinine, cystatin C, and BTP in kidney transplant recipients.

Study Design

Cross-sectional study.

Setting & Participants

207 kidney transplant recipients with stable kidney function.

Predictors

GFR, age, race, sex, body mass index, albumin level, proteinuria, smoking status, prednisone, and calcineurin inhibitor and mycophenolate mofetil use.

Outcomes & Measurements

Multiple linear regression analysis was used to examine the relationship between predictor variables and cystatin C, BTP, and creatinine levels. GFR was measured by using technetium 99m–radiolabeled diethylenetriaminepentaacetic acid clearance.

Results

After adjusting for GFR, cystatin C and BTP levels were significantly lower in women compared with men. Greater albumin concentration was associated with significantly lower cystatin C and BTP concentrations. There was a statistically significant, but clinically small, association between body mass index and cystatin C level, but no association between the other demographic variables or medications analyzed.

Limitations

Predominantly white population; results may not be applicable to other racial groups.

Conclusion

Important nonrenal factors can influence BTP and cystatin C concentrations and need to be considered when interpreting BTP and cystatin C values in kidney transplant patients.

Section snippets

Study Population

Adult kidney transplant recipients followed up at the Ottawa Hospital, Ottawa, Canada, who were at least 6 months posttransplantation with stable kidney function (<20% change in serum creatinine level over the previous 2 measurements) were eligible to participate. Patients were excluded if they were pregnant or breast-feeding, unwilling or unable to provide consent, or likely to die of another comorbid disease or require dialysis therapy or retransplantation within the next 3 months or had

Demographics and Clinical Characteristics

Table 1 lists baseline characteristics of the study population (n = 207). The majority (92%) of patients were white, and only 2% were black. Sixty-four percent of patients were men, and average BMI was 28.2 ± 5.3 kg/m2. Patients had a wide range of kidney function that encompassed all 5 stages of the National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (KDOQI) chronic kidney disease classification system.46 All except 3 patients were on prednisone therapy, and median daily

Discussion

This study characterized important associations between simple clinical parameters and levels of serum analytes used to estimate GFR in kidney transplant recipients. Women were found to have lower BTP, cystatin C, and serum creatinine concentrations; however, the magnitude of the difference was greatest for serum creatinine level. There was no effect of such commonly used immunosuppressive medications as prednisone, mycophenolate mofetil, cyclosporine, or tacrolimus. Age and race were not

Acknowledgements

We thank the staff and patients from the renal transplant program that participated in the study; the staff of the Nuclear Medicine Department at Ottawa Hospital for assistance with DTPA GFR measurements; and the coordinators at the Kidney Research Centre for invaluable assistance in conducting this study.

Support: This study was funded by The Physicians' Services Incorporated Foundation (Grant No. R03-59) and Astellas Pharma Canada. Instrumentation and reagents to measure cystatin C were

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    Originally published online as doi: 10.1053/j.ajkd.2009.06.003 on July 21, 2009.

    C.A.W. and A.A. contributed equally to this work.

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