Estimation of glomerular filtration rates before and after orthotopic liver transplantation: evaluation of current equations

Chronic kidney disease in solid-organ transplantation

As the long-term survival of nonrenal solid-organ transplant recipients continues to improve, more complications related to transplantation occur. Among the most serious is chronic kidney disease (CKD). Although CKD was previously thought to only clinically affect a minority of this population, closer measurements of kidney function and monitoring of CKD complications now show that CKD will affect a significant number, if not a majority, of transplant recipients-particularly the long-term survivors who often have excellent function of their primary allograft. This article will review the incidence, risk factors, treatment, and outcomes of patients who develop CKD after heart, liver, and lung transplantation.

Estimating pediatric glomerular filtration rates in the era of chronic kidney disease staging

With the use of information from a database of pediatric patients with concomitant nuclear GFR and serum creatinine (Cr), estimated GFR equations were derived on the basis of local laboratory methods and population. These formulas then were compared with those recommended by the National Kidney Foundation for estimating GFR in children. For this, their ability to estimate accurately an individual's true GFR and chronic kidney disease stage, identify patients whose true GFR was <60 ml/min per 1.73 m(2), and to identify correctly deterioration in an individual's GFR over time was compared. Next, two methods to estimate GFR in children without the use of height or weight were developed. The first was a height- and weight-independent formula; the second was a novel approach using the Schwartz formula and calculating a Cr cutoff based on age-based estimates of height and GFR level of interest, i.e., <60 ml/min per 1.73 m(2). Our results suggest that if local laboratory constants are derived and a height is known, then the Schwartz formula offers the most accuracy with least mathematical complexity to perform in the clinical setting. If height is not available but the local laboratory constants have been derived, then the British Columbia's Children's Hospital 2 formula is of value; however, in the setting of estimating pediatric renal function in the outpatient laboratory, where neither of these factors is commonly known, an approach whereby a Cr cutoff for a GFR of interest is developed is suggested. Provided are Cr levels that are based on a reference method of Cr measurement to facilitate this approach for the clinician.

Calculation of glomerular filtration rate based on cystatin C in cirrhotic patients

BACKGROUND

Plasma creatinine and creatinine clearance are of limited value for the estimation of renal function in cirrhotics. In these patients, cystatin C (Cys C) has been proposed as an alternative marker of glomerular filtration rate (GFR) and Cys C-based equations for calculation of GFR have been developed in non-cirrhotic patient cohorts.

METHODS

We retrospectively analyzed correlation, bias, precision and accuracy of two Cys C-based formulae (Larsson and Hoek) for GFR estimation in comparison with two creatinine-based equations (Cockroft & Gault and MDRD). The Cys C was determined by an immunonephelometric method. The GFR was measured by means of inulin clearance in 44 consecutive patients with liver cirrhosis.

RESULTS

On average, inulin clearance was 28.3 (95% CI: 29.2-41.3 ml/min/1.73 m2). Creatinine as well as Cys C-based equations overestimated the true GFR by 105-154%. However, Cys C-based equations showed significantly lower bias and higher precision than the creatinine-based formulae. Correlation and accuracy tended to be better with the Hoek and Larsson equation than with the Cockroft & Gault or MDRD formulae. Hoek and Larsson equations showed a similar diagnostic performance in all statistical procedures.

CONCLUSION

Our data suggest a significant improvement of GFR estimation in liver cirrhotics by means of the Cys C-based Hoek and Larsson formulae. However, all estimates remain a crude approximation of true GFR and thus cannot replace gold standard methods.

Endothelin activation and postoperative renal failure after human liver transplantation

Renal failure is an established risk factor for impaired patient outcome after orthotopic liver transplantation (OLT). As the endothelin pathway is known to be involved in the development of acute renal failure (ARF), we designed a study to clarify its role in ARF following OLT. Twenty consecutive patients with intact kidney function scheduled for their first OLT were prospectively studied. Plasma big endothelin-1 (ET-1) levels were measured before surgery, after graft reperfusion, and on the first and second postoperative day. According to postoperative glomerular filtration rate (GFR), patients were assigned to the acute renal dysfunction group (ARDF) and the non-ARDF group. Each patient's GFR was estimated according to the 4-variable formula used in the modification of diet in renal disease before surgery, daily within the first postoperative week, and at 1, 3, 12, and 24 months after surgery. Postoperative mean big ET-1 levels correlated significantly with the maximum percent decrease of GFR within 3 days after OLT (P < 0.01). The proportion of patients who developed ARDF was significantly correlated to mean postoperative big ET-1 quartiles (P < 0.01). In the ARDF group, the percent decrease of GFR within 24 months was significantly higher (P < 0.05) as compared to the non-ARDF group. In conclusion, patients who develop ARDF immediately after OLT do not fully recover to baseline regarding long-term kidney function. Short-term GFR was significantly correlated with postoperative big ET-1 plasma levels, suggesting renal dysfunction is mediated by the activated endothelin system.

Evaluation of renal function in liver transplant recipients receiving daclizumab (Zenapax), mycophenolate mofetil, and a delayed, low-dose tacrolimus regimen vs. a standard-dose tacrolimus and mycophenolate mofetil regimen: a multicenter randomized clinical trial

Posttransplant chronic renal failure, secondary to calcineurin inhibitor agents, is emerging as a major problem in liver transplantation. We report a randomized clinical trial comparing daclizumab, delayed low-dose tacrolimus (target trough level 4-8 ng/mL, starting day 4-6), Investigational Arm (n = 72), to standard tacrolimus induction/maintenance dosing, Standard Arm (n = 76), with mycophenolate mofetil and tapering corticosteroids in both study arms. The end-points were renal function indicated by the Modification of Diet in Renal Disease (MDRD). There was no significant difference in patient survival (86.6% Investigational Arm vs. 92.9% Standard Arm; P = 0.21) or acute rejection (23.2% vs. 27.7%, respectively; P = 0.68). Statistically significant differences in median glomerular filtration rate (GFR) were found in favor of the Investigational Arm. With the CG equation, the GFR at the end of the first week was 110.7 vs. 89.6 mL/min (P = 0.019) without significant differences thereafter. With the MDRD, statistically significant differences extended to the first posttransplant month (86.8 vs. 70.1 mL/min/1.73 m(2); P < 0.001) with and was seen at month 6 (75.4 vs. 69.5 mL/min/1.73 m(2); P = 0.038). In conclusion, delayed low-dose tacrolimus, in combination with daclizumab and mycophenolate mofetil, preserves early renal function post-liver transplantation without the cost of increased acute rejection.

Performance of the Cockcroft-Gault and Modification of Diet in Renal Disease Equations in Estimating GFR in Ill Hospitalized Patients

BACKGROUND

Estimating glomerular filtration rate (GFR) in severely ill inpatients is clinically important for therapeutic interventions and prognosis, but notoriously difficult to do accurately. The Modification of Diet in Renal Disease (MDRD) equation and Cockcroft-Gault (CG) formula are widely used to estimate renal function in sick hospitalized patients; however, neither method has been validated in this setting.

METHODS

Iodine 125-iothalamate clearances (iGFR) performed in 107 sick inpatients with renal dysfunction were compared with estimated GFRs (eGFRs) from the 6- and 4-variable MDRD (MDRD eGFR) and CG (CG eGFR) equations.

RESULTS

Mean serum creatinine (SCr) level was 3.5 +/- 2.0 mg/dL (309 +/- 177 micromol/L), and mean iGFR was 17.1 +/- 17.9 mL/min/1.73 m2 (0.29 +/- 0.30 mL/s/1.73 m2). Six-variable MDRD eGFR was 22.5 +/- 17.4 mL/min/1.73 m2 (0.38 +/- 0.29 mL/s/1.73 m2), 4-variable MDRD eGFR was 23.9 +/- 16.3 mL/min/1.73 m2 (0.40 +/- 0.27 mL/s/1.73 m2), and CG eGFR was 26.0 +/- 17.1 mL/min/1.73 m2 (0.43 +/- 0.29 mL/s/1.73 m2). Blood urea nitrogen (BUN)/SCr ratios greater than 20 were seen in 58% of patients. Overall, the CG and MDRD equations overestimated iGFR, with poor agreement. Overestimation of at least 25% of measured iGFR was seen in 63%, 67%, and 70% of all inpatients when using the 6-variable MDRD, 4-variable MDRD, and CG equations, respectively. Accuracy of eGFR within 50% of measured iGFR was 55% for the 6-variable MDRD equation, 49% for the 4-variable MDRD equation, and 40% for the CG formula. The performance of both methods deteriorated further in patients with a BUN/SCr ratio greater than 20.

CONCLUSION

Estimation equations are performed poorly compared with iGFR and are not reliable measures of actual level of function in sick hospitalized patients, especially those with a high BUN/SCr ratio. Although use of the 6-variable MDRD equation provides a better estimation of GFR, it still is unsuitable for clinical application in this population.

MDRD equations for estimation of GFR in renal transplant recipients

After renal transplantation monitoring and detection of slight-to-moderate changes in GFR is a prerequisite for an optimal patient management. Recently, several equations to estimate GFR were developed and verified in the MDRD study cohort. However, little is known about the application of the MDRD formulas in the setting of renal transplantation. We prospectively conducted a study of the GFR estimates of the Cockcroft and Gault (C&G), MDRD6-, MDRD7 and the abbreviated MDRD (aMDRD) with the true GFR as measured by (99m)Tc-DTPA clearance in 95 consecutive patients 6.5, 5.3-7.7 years (mean, 95% CI) after renal transplantation. On average the DTPA clearance was 37.4, 34.4-40.4 mL/min/1.73 m(2), which differed significantly from estimates of GFR by C&G (52.6, 48.3-56.9 mL/min/1.73 m(2)), MDRD7 (44.8, 40.7-49.0 mL/min/1.73 m(2)), MDRD6 (43.8, 39.9-47.7 mL/min/1.73 m(2)) and aMDRD (46.6, 42.4-50.9 mL/min/1.73 m(2)). Bias was lowest for MDRD6 (6.4 mL/min/1.73 m(2)) and highest for C&G (15.2 mL/min/1.73 m(2)). Precision was similar for MDRD7 and aMDRD (10.6 and 11.1 mL/min/1.73 m(2)) but significantly better for MDRD6 (8.6 mL/min/1.73 m(2); p < 0.035). Accuracy within 50% of real GFR was 55.8% for C&G, 83.2% for aMDRD, 87.4% for MDRD7 and 90.5% for MDRD6. MDRD equations perform significantly better than the commonly used C&G formula. Moreover, the MDRD6 equation provides the best diagnostic performance, and should therefore be preferred in renal transplant recipients.