Scholarly article on topic 'Renal function and MELD: Being direct is better'

Renal function and MELD: Being direct is better Academic research paper on "Basic medicine"

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Academic research paper on topic "Renal function and MELD: Being direct is better"

Editorial

EUROPEAN ASSOCIATION FOR THE STUDY OF THE LIVER |

JOURNAL OF HEPATOLOGY

Renal function and MELD: Being direct is betterq

Stevan A. Gonzalez, James F. Trotter*

Division of Hepatology, Baylor Regional Transplant institute, Baylor All Saints Medical Center, Fort Worth and Baylor University

Medical Center, Dallas, TX, USA

Renal insufficiency is common in patients with end-stage liver disease (ESLD) and is strongly linked to survival in those awaiting liver transplantation. In liver patients, renal dysfunction is largely due to a circulatory disturbance characterized by a low systemic vascular resistance and decreased effective arterial volume leading to impaired renal excretion of solute-free water, dilutional hyponatremia and ultimately hepatorenal syndrome (HRS) [13]. Once a patient develops type I HRS, the median survival without treatment is as low as 2 weeks, while the median survival in type II HRS is approximately six months; both a significant decrease in survival compared to patients without HRS [1,4,5]. The diagnosis and severity of HRS is dependent on two biochemical markers, serum sodium and creatinine, both of which are independently associated with an increased risk of mortality in cirrhosis [6-14]. Their importance is underscored by inclusion in the most widely utilized predictive survival function, the model for end-stage liver disease (MELD) score or Na-MELD, where the addition of serum sodium significantly improves [914] the performance of MELD. Whether sodium will be included into the MELD score (for prioritizing liver transplantation candidates) remains in question for two reasons. Serum sodium levels are easily manipulated with water ingestion and the administration of vaptans. In addition, hyponatremia may have a negative impact on post-transplant complications and survival, [15-17] although recent data have brought this into question [18].

While serum sodium and creatinine are important predictors of mortality in cirrhosis, their relationship to the most sensitive gauge of renal function, measured glomerular filtration rate (GFR), is more complicated. To the degree that renal handling of sodium and water is altered in cirrhosis, serum sodium is determined by renal function. However, serum sodium only correlates roughly with GFR. With regard to serum creatinine, numerous studies have documented its incongruity with measured as well as estimated GFR. Specifically, creatinine typically overestimates renal function in patients listed for liver transplantation [19,20], particularly in those with the lowest GFR. This discrepancy may be due to lower

q Editorial on "Serum sodium, renal function, and survival of patients with endstage liver disease". Lim Y-S, Larson TS, Benson JT, Kamath PS, Kremers WK, Therneau TM, Kim WR. J Hepatol 2010;52:523-528.

* Corresponding author. Address: Division of Hepatology, Baylor University Medical Center, 4th Floor Roberts Building, 3500 Gaston Avenue, Dallas, TX 75246, USA. Tel.: +1 214 820 8500; fax: +1 214 820 8168. E-mail address: james.trotter@baylorhealth.edu (J.F. Trotter).

serum creatinine levels in liver patients caused by decreased hepatic creatine production, poor nutrition, decreased muscle mass, and increased tubular secretion of creatinine [21,22]. Furthermore, in jaundiced patients, elevated bilirubin levels may interfere with commonly used assays leading to further variability in serum creatinine and MELD scores [22].

With this background Lim et al. have addressed the following issue: while renal disease and its serum markers, i.e., serum sodium and creatinine, are important predictors for survival in cirrhosis, their correlation with the gold-standard of renal function, measured GFR, is poor. Therefore, could the predictive capacity of the MELD score be improved by replacement of creat-inine (and sodium) with measured GFR? This is a clever analysis which could only be conducted in very few places, because only a small number of liver transplant programs routinely measure GFR with iothalamate (or similar methodology) in their liver transplant candidates. Its rarity is likely due to the cumbersome nature of the test, requiring pre-test hydration and careful collection of timed samples over several hours after iothalamate administration. Consequently, GFR is usually measured only once during the evaluation phase of transplant candidacy and is poorly suited for critically ill or hospitalized patients. Lim et al. analyzed the effect of the measured GFR on the predictive capacity of MELD and we learn several key points from their study. First, there was an association between one-year mortality and measured renal function. While this is not a surprise to experienced clinicians, the strength of the association is remarkable. The one-year mortality rates for patients with a measured GFR of 30-60 ml/min and <30ml/min were more than threefold and fivefold higher, respectively, compared to patients with normal renal function (GFR > 60 ml/min). In fact, GFR had a significant linear association with survival, independent of MELD score. Second, measured GFR was superior to serum creatinine as a predictor of mortality, in a model incorporating bilirubin, INR, and GFR (in the place of serum creatinine). Finally, the effect of serum sodium on the model loses significance when GFR is included. Thus, inclusion of sodium in the MELD score may not be necessary if measured GFR (or perhaps a yet-to-be-determined marker) is used to determine renal function.

There are some qualifications to the findings in this study. The cohort is derived from the pre-MELD era. Consequently, the analyzed patients are likely to be less sick (median serum creatinine = 1.0 mg/dl and serum sodium 137 mEq/L) and have different demographics (only 20% with hepatitis C) than current

Journal of Hepatology 2010 vol. 52 I 622-623

liver transplant recipients. In addition, the total waiting list mortality (9.2%) over the course of this multi-year study was quite low, compared to current standards. These differences might limit the applicability of the authors' findings in our current cohort of liver transplant candidates. Finally, the improvement reported by the authors, while statistically significant, is relatively small between MELD (C-statistic = 0.780) and MELD with GFR (C-statistic = 0.792).

Overall, the authors have broadened our understanding of the impact of renal function, and its markers, on the MELD score. Modification of the MELD score to include measured GFR may indeed improve the predictive accuracy of the model, yet challenges arise in its general applicability. Serum creatinine and serum sodium are easily accessible to all clinicians evaluating liver transplant candidates. In contrast, methods to assess GFR, including clearance of compounds such as iothalamate, require specialized laboratory resources not readily available at all liver transplant centers. However, these findings suggest that identification of more accurate laboratory tests for renal function might improve the predictive function of the MELD score. Perhaps the most likely candidate for this role is serum cystatin C. Unfortunately, there is relatively little data available assessing this marker in cirrhotic patients. Nevertheless, the available data suggests that, compared to serum creatinine, cystatin might provide a slightly more accurate estimate of renal function and therefore could improve the predictive capacity of the MELD [23-27]. Whether this or any other marker could improve the function of MELD will require further careful analysis.

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JOURNAL OF HEPATOLOGY

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