Evaluation of plasma cystatin C as a marker for glomerular filtration rate in patients with type 2 diabetes.

AIM: To evaluate plasma cystatin C as a marker of the glomerular filtration rate in patients with type 2 diabetes and their age and sex-matched controls. MATERIALS AND METHODS: Forty-seven patients with one decade of type 2 diabetes and 51 non-diabetic control subjects were studied. Plasma cystatin C was measured by particle-enhanced turbidimetric immunoassay in a new application for the Hitachi 704 analyzer. For comparison, plasma creatinine and creatinine clearance were measured. The plasma clearance of 51Cr-EDTA by the single injection method was utilized as reference. RESULTS: In patients with type 2 diabetes the correlation coefficient between plasma cystatin C and the plasma clearance of 51Cr-EDTA was 0.774 (Spearman's coefficient) and that between plasma creatinine and the plasma clearance of 51Cr-EDTA was 0.556 (p = 0.001 for the difference). The correlation between creatinine clearance and the plasma clearance of 51Cr-EDTA was 0.411. In receiver operating characteristic (ROC) curve analysis the diagnostic accuracy of plasma cystatin C was significantly better than that of plasma creatinine (p = 0.047) or creatinine clearance (p = 0.001). The best diagnostic efficiency (98%) for cystatin C was obtained when the cut-off limit was set at 1.32 mg/l. In the control group the correlation coefficients were: between cystatin C and the plasma clearance of 51Cr-EDTA 0.627, between creatinine and the plasma clearance of 51Cr-EDTA 0.466 and between creatinine clearance and the plasma clearance of 51Cr-EDTA 0.416. The area under the ROC plot curve of cystatin C was also greatest in the control group, but the diagnostic accuracy of cystatin C was marginally better than that of either plasma creatinine (p = 0.05) or creatinine clearance (p = 0.08). Among the control subjects various non-renal causes may have interfered with cystatin C concentrations reducing the correlations. CONCLUSIONS: Cystatin C measurement is a more sensitive and specific test for GFR in patients with type 2 diabetes than plasma creatinine or its clearance, when GFR is normal or only slightly reduced. If an elevated cystatin C concentration is found, non-renal factors have to be excluded. The turbidimetric application described here can easily be applied for most clinical chemistry analyzers and is therefore useful in daily clinical practice.

Cystatin C as a marker for glomerular filtration rate in pediatric patients.

Cystatin C is a non-glycated 13-kilodalton basic protein produced by all nucleated cells. The low molecular mass and the basic nature of cystatin C, in combination with its stable production rate, suggest that the glomerular filtration rate (GFR) is the major determinant of cystatin C concentration in the peripheral circulation. Recently published studies have shown that cystatin C correlates more strongly than creatinine with GFR measured using the 51Cr-EDTA clearance. The aim of this study was to evaluate serum cystatin C as a marker for GFR in children. GFR was determined on medical indications using the 51Cr-EDTA technique in pediatric patients (2-16 years) in our renal unit. Simultaneously their cystatin C and creatinine concentrations were also measured. Of our 52 patients, 19 had a reduced renal function (

Measurement of serum ionized magnesium in CAPD patients.

OBJECTIVE: To evaluate the magnesium status of continuous ambulatory peritoneal dialysis (CAPD) patients using a new method for assessing the level of the ionized fraction of serum magnesium. DESIGN: Serum ionized magnesium was measured in CAPD patients using the ion-selective electrode for Mg2+. SETTING: The Dialysis Unit of Tampere University Hospital. PATIENTS: Twenty-six patients on CAPD (age: 21-81 years, mean 54 +/- 16 years; duration of CAPD: 3-52 months, mean 13 months), and 26 sex- and age-matched healthy controls. RESULTS: Both serum ionized magnesium (0.73 +/- 0.11 mmol/L vs 0.56 +/- 0.07 mmol/L, p < 0.001) and total magnesium (1.11 +/- 0.22 vs 0.81 +/- 0.08 mmol/L, p < 0.01) were higher in CAPD patients than in sex- and age-matched controls. The ionized magnesium fraction of total magnesium was slightly lower in dialysis patients in spite of the fact that 16/26 patients had serum albumin less than 36 g/L. Hypermagnesemia (mean serum ionized magnesium 0.78 +/- 0.10 mmol/L) was observed in the 13 of 26 patients with 0.75 mmol/L Mg2+ dialysate; those with lower magnesium dialysate (Mg2+ 0.50 mmol/L in 10/26 and Mg2+ 0.25 mmol/L in 3/26) had mean serum ionized magnesium at the upper normal margin (0.69 +/- 0.10 mmol/L). CONCLUSION: In CAPD patients with Mg2+ 0.5-0.75 mmol/L in their dialysis fluid, both serum ionized and total magnesium concentrations were higher but the ionized/total magnesium ratio was lower than in healthy control subjects. Use of ion-selective electrodes to measure ionized magnesium may be a more useful methodology than measuring total magnesium in the evaluation of magnesium status of CAPD patients, because it is not influenced by hypoalbuminemia or increased complexed fraction of magnesium often present in dialysis patients.

Bilirubin and metamizol do not interfere with the randox enzymatic creatinine test. An evaluation of a new enzymatic creatinine determination method.

We evaluated the new commercially available enzymatic test kit for creatinine (Randox Laboratories Ltd. Ardmore, Crumlin, UK). The test correlated well with the reference HPLC method (yenz = 0.98x + 1.4; r = 1.00; n = 72). The correlations with the Jaffe method (yenz = 1.00x + 14.1; r = 0.99; n = 72) and the dry slide technique (yenz = 1.07x + 4.1; r = 1.00; n = 72) were also good, but these techniques gave slightly higher creatinine results than the HPLC or the Randox enzymatic method. This new test is insensitive to bilirubin interference. It has been reported that patients receiving metamizol showed unusually low values of creatinine, when determined enzymatically, but this drug does not interfere with the Randox method. The test evaluated is more specific than enzymatic methods published earlier and it provides an attractive alternative to the traditional picrate test.

Serum C-reactive protein concentration in acute myocardial infarction and its relationship to mortality during 24 months of follow-up in patients under thrombolytic treatment.

OBJECTIVES: We studied the relationship between serum C-reactive protein and mortality in acute myocardial infarction. BACKGROUND: Early recanalization of an infarct-related coronary artery is considered to be an essential prerequisite for reducing mortality by thrombolytic treatment in acute myocardial infarction. It also reduces the inflammatory reaction caused by acute myocardial infarction and is measurable by determination of serum C-reactive protein concentrations. We therefore studied the prognostic value of determining serum C-reactive protein in acute myocardial infarction. METHODS: We measured serum C-reactive protein concentrations daily for 6 days and creatine kinase, as well as its MB isoenzyme concentrations twice a day, for 3 days after a myocardial infarct, in 188 consecutive patients selected for thrombolytic therapy and treated in the same University Hospital Coronary Care Unit. The highest serum concentrations were related to total mortality as well as to the causes of death 3, 3-6, 6-12 and 12-24 months after the onset of the myocardial infarction. RESULTS: The highest serum concentrations of serum C-reactive protein were observed 2 to 4 days after the onset of myocardial infarction. The mean value of the highest serum concentration of C-reactive protein in patients who survived the whole 24-month study period was 65 mg. 1(-1), with the 95% confidence intervals for the mean ranging from 58 to 71. The corresponding values in those who died within 3, 3-6, 6-12 and 12-24 months were 166 (139-194), 136 (88-184), 85 (52-119) and 74 (38-111) mg.1(-1), respectively. The values in those who died within 3 and 3-6 months of the infarction differed statistically significantly from the values in those who survived the whole period (P < 0.001 and P < 0.05, respectively). In patients who died due to congestive heart failure the mean highest serum C-reactive protein concentration was 226 (189-265) mg.1(-1). In those who suffered sudden cardiac death and those who died from a new myocardial infarction or non-cardiac causes, the respective values were 167 (138-196), 64 (38-89) and 48 (10-86) mg. 1(-1). The values in those who died due to congestive heart failure and those suffering sudden cardiac death differed statistically significantly (P < 0.001) from the values of those who survived or died due to other causes. The highest serum concentrations of creatine kinase or its MB isoenzyme were not associated with mortality in this study. CONCLUSIONS: High serum C-reactive protein concentrations in acute myocardial infarction patients treated with thrombolytic drugs predict increased mortality up to 6 months following the infarction. Accordingly, reduction of inflammatory reaction by successful thrombolytic treatment may make an important contribution to the survival benefit of thrombolytic treatment of acute myocardial infarction.