Michela Ardini

Cystatin C, β2-microglobulin, and retinol-binding protein as indicators of glomerular filtration rate: comparison with plasma creatinine

BACKGROUND The aim of this study was to assess the diagnostic accuracy of plasma levels of three low-molecular weight proteins cystatin C, beta 2-microglobulin, and retinol-binding protein, as indicators of impairment of glomerular filtration rate in comparison with plasma creatinine. METHODS Glomerular filtration rate (GFR) was measured in 110 patients (51 M and 59 F, aged 18--79 years); creatinine (Creat), cystatin C (Cys), beta 2-microglobulin (beta 2M), and retinol-binding protein (RBP) were determined on the same day. The correlation coefficients between the different markers and GFR were determined. Receiver-operating characteristics (ROC) analysis was performed to assess their diagnostic accuracy. Furthermore, the relationship between plasma levels of the examined markers of GFR and body weight, height, fat-free mass (FFM) and body cell mass (BCM) was determined. FFM and BCM were calculated by means of total body electrical impedance measurement. RESULTS Serum concentrations of Cys, beta 2M and RBP increase progressively with the reduction of GFR. The magnitude of the increase in blood levels of Creat and beta 2M was higher than the increase of Cys, and much more than that of RBP, in particular in patients with GFR<20 ml/min/1.73 m(2). The correlation coefficients between GFR and 1/plasma concentrations were 0.647 for Creat, 0.651 for Cys, 0.731 for beta 2M, and 0.406 for RBP. ROC analysis indicated that the accuracy of beta 2M and Cys, as indicators of different degrees of GFR impairment (<80, <60, and <40 ml/min per 1.73 m(2)), was similar to that of Creat, while the diagnostic accuracy of RBP resulted significantly lower than that of Creat for any level of GFR. In patients without renal failure (GFR>40 ml/min per 1.73 m(2)), plasma concentrations of Creat were positively correlated with body weight (P<0.01), height (P<0.01), FFM (P<0.001) and BCM (P<0.001). Serum concentrations of RBP resulted correlated with FFM (P<0.05) and BCM (P<0.05), while no correlation was found between anthropometric data and Cys and beta 2M. CONCLUSION Cystatin C and beta 2-microglobulin have a diagnostic accuracy very similar to that of creatinine, while retinol-binding protein is not an adequate marker of glomerular filtration.

Serum levels of beta-trace protein and glomerular filtration rate--preliminary results.

The aim of this study was to evaluate the relationship between serum levels of beta-trace protein (BTP), a low molecular weight (MW) protein, and glomerular filtration rate (GFR). GFR and serum levels of BTP, and for comparison creatinine (Creat), cystatin C (Cys) and beta 2-microglobulin (beta 2M), were measured in 60 patients, with renal function ranging from normality to advanced renal failure. Serum levels of BTP progressively increased with the reduction of GFR. A good correlation was found between GFR and serum levels of BTP (r=0.918), Creat (r=0.932), Cys (r=0.937), and beta 2M (r=0.924). Furthermore, no statistically significant difference was found between BTP and Creat, Cys, beta 2M, as indicators of a moderate GFR impairment. These preliminary data indicate that BTP might be suitable as an indicator of GFR.

Prediction of Glomerular Filtration Rate From Body Cell Mass and Plasma Creatinine

The gold standards for the measurement of glomerular filtration rate (GFR) are inulin clearance and radioisotopic methods. However, creatinine clearance is the most used test to evaluate GFR in clinical practice. Its adequacy is questionable, since its repeatability is quite poor, mainly due to errors in the collection of urine. The aim of this study was to evaluate a new method to predict GFR from the body cell mass (BCM) and plasma creatinine (Pcr), avoiding urine collection. The values of BCM were obtained in 275 adult renal patients with different renal function, ranging from normality to advanced renal failure. The relationship of GFR (clearance of (99m)Tc-DTPA) with BCM and Pcr was calculated in the first 85 patients. A highly significant linear correlation was found between GFR and the ratio BCM/Pcr. Thereafter, GFR was predicted from BCM and Pcr (BCM GFR) with formulas derived from the relationships found between GFR and the ratio BCM/Pcr. For comparison, GFR was predicted also according to other prediction formulas: Cockcroft and Gault (CG GFR), and the simplified MDRD formula (MDRD GFR). BCM GFR gave a more precise estimate of GFR than CG GFR and MDRD GFR. In fact, BCM GFR had the best correlation and agreement with true GFR ((99m)Tc-DTPA). Furthermore, CG GFR and MDRD GFR markedly overestimated true GFR. Finally, the error of prediction of BCM GFR was definitely lower than that of the two other estimates of GFR. GFR can be predicted from BCM and plasma creatinine. This method, which is very simple and accurate, seems suitable to establish the adequate dosage of drugs cleared by the kidneys.

Parathyroid hormone and large related C-terminal fragments increase at different rates with worsening of renal function in chronic kidney disease patients. A possible indicator of bone turnover status?

BACKGROUND The intact parathyroid hormone (PTH) serum value has been the non-invasive biomarker of choice for the early diagnosis of renal bone disease in the chronic kidney disease (CKD) patient population. It has now been known that the intact PTH assay value is the sum of 1-84 PTH (true hypercalcemic PTH) and large C-terminal PTH fragments, mainly 7-84 PTH, a fragment with hypocalcemic hormone actions. AIM The aim of this study was to investigate the differences among the different functional stages of CKD in the following PTH parameters: intact PTH, 1-84 PTH, 7-84 PTH, and the ratio 1-84 PTH/7-84 PTH. GFR (clearance of 99mTc-DTPA) was measured in 164 (85 males and 79 females) adult CKD patients with different degrees of renal function impairment (serum creatinine 0.50 12.1 mg/dl, mean 2.00). PATIENTS AND METHODS Plasma concentrations of calcium, phosphate, 1-84 PTH and intact PTH were also measured. The value of 7-84 PTH was calculated as the difference between intact PTH and 1-84 PTH. The reduction of, GFR was accompanied by an increase of intact PTH, with a prevalent increase of 7-84 PTH over 1-84 PTH, resulting in a decrease of the ratio 1-84 PTH/7-84 PTH. RESULTS The values of 7-84 PTH showed a discrimination between Stages 1 and 2 (GFR > 60 ml/min ) and Stage 3 (GFR 30 60 ml/ min) CKD patient populations. In fact, 7-84 PTH was already significantly increased in patients at CKD Stage 3. The analysis of individual patients indicated that a low value (< 1.4) of the ratio 1-84 PTH/7-84 PTH, suggestive for low bone turnover, was already found in more than 20% of CKD Stage 3 patients. CONCLUSION The results of the present study demonstrate that the reduction in GFR is accompanied by a higher increase in 7-84 PTH with respect to 1-84 PTH, which suggests the possibility that bone metabolism and calcemic status are already reduced in patients with moderate renal failure (CKD Stage 3).

Renal effects of cardiac angiography with different low-osmolar contrast media.

The aim of this study was to evaluate the renal effects of cardiac angiography performed with three low-osmolar contrast media (CM): iopromide (IPR), ioversol (IVR) and ioxaglate (IOX). IPR and IVR are non-ionic CM, IOX is an ionic CM. Different parameters of renal function were determined before and 6, 24, 48, 72 hrs after angiography in 45 patients: 15 patients were examined with IPR, 15 with IVR and 15 with IOX. Glomerular effects – Plasma creatinine increased slightly at the 24th hour after IVR and IOX and at 48 hours after IOP. A significant increase in plasma β2-microglobulin was observed, at the same time, only after IOX. A significant decrease in creatinine clearance was found at 6 hours after IOX. No significant variations in glomerular filtration rate (GFR) and in effective renal plasma flow were found at 48 hours after cardiac angiography; while filtration fraction was significantly reduced after IOP and IOX. Tubular effects – A marked decrease in sodium clearance and a relevant increase of urinary activities of different tubular enzymes were found after cardiac angiography with all CM, but were more evident after the ionic CM IOX, than after the two non-ionic agents. These tubular effects reached the maximum between 6 and 24 hours and returned to baseline within 72 hrs after cardiac angiography. In conclusion, slight glomerular effects were observed mainly after IOX. A reversible tubular malfunction was found with the three low-osmolar CM and was more evident after ionic CM IOX, thus suggesting that other mechanisms, besides osmolarity, play a role in tubular toxicity due to CM. In no patient did the glomerular and tubular effects of CM have a clinical relevance.

Renal impairment in patients with ovarian cancer

OBJECTIVE To investigate the prevalence of renal impairment in patients with ovarian cancer at the time of the diagnosis. STUDY DESIGN Creatinine clearance was estimated according to Cockcroft and Gault (C&G Ccr), glomerular filtration rate (GFR) was determined as renal clearance of 99mTc-DTPA, and renal ultrasound was performed in 60 consecutive patients with newly diagnosed ovarian cancer. RESULTS A 28% of the total population studied had a GFR <60 ml/min/1.73 m(2). A moderate/severe dilation of the upper urinary tract was found in 12% of patients. The length of kidneys ranged between 9.0 and 13.5 cm, and a statistically significant correlation was found between kidney length and values of GFR. CONCLUSION A reduction in renal function and a moderate to severe dilation of upper urinary tract frequently occur in patients with ovarian cancer at the time of the diagnosis.

Dose individualization can minimize nephrotoxicity due to carboplatin therapy in patients with ovarian cancer.

Carboplatin (Carbo-Pt), an alkylating agent cleared from the plasma through glomerular filtration, is commonly used for the treatment of ovarian cancer. When administered at high dosage or to patients with reduced renal function, Carbo-Pt may be nephrotoxic. The dose of Carbo-Pt is calculated with Calvert formula, using the value of 24-hour creatinine clearance (24h Ccr) as an estimate of glomerular filtration rate (GFR). The aim of this study was to evaluate the possibility of individualizing the dose of Carbo-Pt using an alternative method to estimate GFR, based on body composition analysis, and then to assess the nephrotoxicity of Carbo-Pt therapy individualized with this new method. First, we evaluated the agreement between GFR (renal clearance of diethylene triamine pentaacetic acid (99mTc-DTPA)), 24h Ccr, and the new estimate of GFR (BCMGFR) calculated on the basis of individual values of body cell mass (BCM) and plasma creatinine. BCMGFR gave a better estimate of GFR than 24h Ccr. Then, we evaluated the nephrotoxicity of a combination chemotherapy based on Carbo-Pt (AUC5-6) in 23 patients affected by ovarian cancer. The dose of Carbo-Pt was adjusted to residual renal function of patients, evaluated as BCMGFR. No case of acute renal failure was observed with this treatment regimen. Urinary excretion of proteins (albumin, β2-microglobulin, and retinol-binding protein) and tubular enzymes, measured as markers of tubular damage, increased significantly and transiently only in the first days after chemotherapy, whereas no evidence of chronic nephrotoxic effect was documented. Dose individualization, using the value of BCMGFR, may minimize nephrotoxicity due to Carbo-Pt therapy.