Cystatin C as a more sensitive indicator of diminished glomerular filtration rate

Cystatin C: current position and future prospects

Cystatin C is a low-molecular-weight protein which has been proposed as a marker of renal function that could replace creatinine. Indeed, the concentration of cystatin C is mainly determined by glomerular filtration and is particularly of interest in clinical settings where the relationship between creatinine production and muscle mass impairs the clinical performance of creatinine. Since the last decade, numerous studies have evaluated its potential use in measuring renal function in various populations. More recently, other potential developments for its clinical use have emerged. This review summarises current knowledge about the physiology of cystatin C and about its use as a renal marker, either alone or in equations developed to estimate the glomerular filtration rate. This paper also reviews recent data about the other applications of cystatin C, particularly in cardiology, oncology and clinical pharmacology.

Review article: renal function assessment in cirrhosis - difficulties and alternative measurements

BACKGROUND

Renal function in patients with cirrhosis is important prognostically, both before and following liver transplantation. Its prognostic impact is reflected by the inclusion of serum creatinine in the model for end-stage liver disease score, which is now used for recipient prioritization on liver transplantation waiting lists in the USA.

AIM

To review the accuracy of the surrogate markers for the assessment of renal function, i.e. glomerular filtration rate, particularly in patients with cirrhosis.

METHOD

We reviewed the available literature in PubMed regarding the markers for GFR evaluation and the factors which affect their accuracy in cirrhosis.

RESULTS

Although creatinine is widely available, it is an unreliable marker of glomerular filtration rate, particularly in patients with cirrhosis. Clearance of exogenous markers is considered the 'gold standard', but this methodology has many drawbacks, particularly poor applicability. Several mathematical formulae for estimated glomerular filtration rate are used to overcome some of these limitations: Cockcroft-Gault and Modification of Diet in Renal Disease formulae are the most frequently applied, but they are based on serum creatinine.

CONCLUSIONS

Due to the inaccuracy of serum creatinine and its derived formulae in estimating glomerular filtration rate, alternative serum markers, such as cystatin C, and new formulae are desirable. These need formal evaluation in patients with cirrhosis so as to have a reliable surrogate of glomerular filtration rate, and to obviate many problems that are associated with using creatinine and estimated glomerular filtration rate.

Clinical chemistry reference database for Wistar rats and C57/BL6 mice

Clinical chemistry data are decisive for evaluating altered organ function or damage in experimental animals. Few publications provide reliable clinical chemistry reference intervals, and analytical methods are often not described. Here, we investigated common clinical chemistry values in adult male and female Wistar rats and C57/BL6 mice (n=30/group). Blood samples were taken and analysed for electrolytes, substrates, metabolites and enzymes. In addition, we investigated cystatin C, an important marker of glomerular dysfunction. All data were obtained using commercially available kits frequently employed in most clinical chemistry laboratories and compared with data from other studies, as well as with human data. Significant gender-specific differences were observed in rats (electrolytes, retention parameters and transaminases) and in mice (cholesterol, glucose). High variability was noted for sodium, potassium, glucose, creatine kinase, lactate dehydrogenase and transaminase levels. Both rodent species showed markedly higher alpha-amylase activity than humans. This report demonstrates significant differences between genders for many analytes in rats and for fewer parameters in mice. Some reference values displayed major discrepancies between rodents and humans.

Serum cystatin C levels to predict serum concentration of digoxin in Japanese patients

Cystatin C (Cys-C) has been recently paid great attention as a better endogenous marker of the glomerular filtration rate than creatinine (Cr). In this study, the usefulness of Cys-C was compared with Cr in terms of the estimation of the steady-state serum trough concentrations of digoxin in Japanese patients. Forty patients treated with digoxin and 56 healthy elderly subjects were participated in this study. The serum levels of Cys-C and Cr in the patients were higher than those in the healthy elderly subjects, but the increase of Cys-C was more predominant in the patients. Their levels were well-correlated for both of the healthy elderly subjects (r=0.691) and patients (r=0.774), but the serum concentrations of digoxin were better correlated with those of the reciprocal values of Cr (r=0.667) than those of Cys-C (r=0.383), presumably due to the fact that digoxin and Cr were excreted via both glomerular filtration and tubular secretion. Cys-C is useful for the substratification of the patients diagnosed to have normal renal function with Cr of < 1.3 mg/dL into those with normal and pseudo-normal renal function, resulting in the corresponding serum concentrations of digoxin.