Mayo Clinic Quadratic Research Articles

Comparison of creatinine-based estimations of glomerular filtration rate in endurance athletes at rest

Several creatinine-based estimates of the glomerular filtration rate (GFR) have been advocated as reliable alternatives to the urinary clearance of exogenous filtration markers. The Cockcroft-Gault (C-G) equation requires a body weight parameter, which was not included in the Modification of Diet in Renal Disease (MDRD) Study and the Mayo Clinic Quadratic Equation (MCQE) formulas. However, there is little information on the lifestyle influences on these equations, especially the intensity and the type of physical activity. We evaluated the differences in the GFR, as estimated by the MDRD, MCQE and C-G equations, in 60 professional male cyclists at rest and 60 healthy sedentary matched controls. Professional cyclists had significantly lower body weight, body mass index and serum creatinine concentration than healthy sedentary individuals. We also observed a significantly higher MDRD-estimated GFR in athletes than in controls (119 mL/min/1.73 m2 vs. 104 mL/min/1.73 m2, p<0.001), whereas the GFR values estimated by both the MCQE (137 vs. 135, p=0.128) and C-G (127 vs. 127, p=0.490) formulas did not differ significantly. As compared to the MDRD values, the mean GFR calculated by the MCQE and C-G formulas was overestimated by 29% and 23% in the sedentary population, and by 17% and 7% in athletes, respectively. A lower bias was observed when comparing C-G with MCQE-estimated values in both the sedentary [mean: -5%, 95% confidence interval (CI): -32% to 22%] and athlete (mean: -6%, 95% CI: -41% to 29%) populations. The correlation among the different equations in healthy sedentary individuals was always significant, whereas the only significant association in the athletes was that between MCQE and C-G values. The results of this study attest that the three most widely used creatinine-based formulas produce significant variations in the estimated GFR in a population of endurance athletes at rest. Probably, the use of C-G or MCQE formulas might be more suitable in this context, as they globally appear more robust against variations of the training regimen.

Glomerular filtration rate estimates decrease during high altitude expedition but increase with Lake Louise acute mountain sickness scores

Acute mountain sickness (AMS) can result in pulmonary and cerebral oedema with overperfusion of microvascular beds, elevated hydrostatic capillary pressure, capillary leakage and consequent oedema as pathogenetic mechanisms. Data on changes in glomerular filtration rate (GFR) at altitudes above 5000 m are very limited. Thirty-four healthy mountaineers, who were randomized to two acclimatization protocols, undertook an expedition on Muztagh Ata Mountain (7549 m) in China. Tests were performed at five altitudes: Zurich pre-expedition (PE, 450 m), base camp (BC, 4497 m), Camp 1 (C1, 5533 m), Camp 2 (C2, 6265 m) and Camp 3 (C3, 6865 m). Cystatin C- and creatinine-based (Mayo Clinic quadratic equation) GFR estimates (eGFR) were assessed together with Lake Louise AMS score and other tests. eGFR significantly decreased from PE to BC (P < 0.01). However, when analysing at changes between BC and C3, only cystatin C-based estimates indicated a significant decrease in GFR (P = 0.02). There was a linear decrease in eGFR from PE to C3, with a decrease of approx. 3.1 mL min(-1) 1.73 m(-2) per 1000 m increase in altitude. No differences between eGFR of the two groups with different acclimatization protocols could be observed. There was a significant association between eGFR and haematocrit (P = 0.01), whereas no significant association between eGFR and aldosterone, renin and brain natriuretic peptide could be observed. Finally, higher AMS scores were significantly associated with higher eGFR (P = 0.01). Renal function declines when ascending from low to high altitude. Cystatin C-based eGFR decreases during ascent in high altitude expedition but increases with AMS scores. For individuals with eGFR <40 mL min(-1) 1.73 m(-2), caution may be necessary when planning trips to high altitude above 4500 m above sea level.

New Predictive Equations Improve Monitoring of Kidney Function in Patients With Diabetes

The Cockcroft-Gault and Modification of Diet in Renal Disease (MDRD) equations poorly predict glomerular filtration rate (GFR) decline in diabetic patients. We sought to discover whether new equations based on serum creatinine (the Mayo Clinic Quadratic [MCQ] or reexpressed MDRD equations) or four cystatin C-based equations (glomerular filtration rate estimated via cystatin formula [Cys-eGFR]) were less biased and better predicted GFR changes. In 124 diabetic patients with a large range of isotopic GFR (iGFR) (56.1 +/- 35.3 ml/min per 1.73 m2 [range 5-164]), we compared the performances of the equations before and after categorization in GFR tertiles. A total of 20 patients had a second determination 2 years later. The Cockcroft-Gault equation was the least precise. The MDRD equation was the most precise but the most biased according to the Bland-Altman procedure. By contrast with the MDRD and, to a lesser extent, the MCQ, three of the four Cys-eGFRs were not biased. All equations overestimated the low GFRs, whereas only the MDRD and Rule's Cys-eGFR equations underestimated the high GFRs. For the subjects studied twice, iGFR changed by -8.5 +/- 17.9 ml/min per 1.73 m2. GFR changes estimated by the Cockcroft-Gault (-4.5 +/- 6.8) and MDRD (-5.7 +/- 6.2) equations did not correlate with the isotopic changes, whereas new equation-predicted changes did: MCQ: -8.7 +/- 9.4 (r = 0.44, P < 0.05) and all four Cys-eGFRs: -6.2 +/- 7.4 to -7.3 +/- 8.4 (r = 0.60 to 0.62, all P < 0.005), such as 100/cystatin-C (r = 0.61, P < 0.005). The new predictive equations better estimate GFR than the Cockcroft-Gault equation. Although the MDRD equation remains the most accurate, it poorly predicts GFR decline, as it overestimates low and underestimates high GFRs. This bias is lesser with the MCQ and Cys-eGFR equations, so they better predict GFR changes.

The Mayo Clinic quadratic equation improves the prediction of glomerular filtration rate in diabetic subjects

Although recommended, both the Cockcroft and Gault formula (CG) and the modification of diet in renal disease (MDRD) equation are not ideally predictive of glomerular filtration rate (GFR) in diabetic subjects; we tested whether the new Mayo Clinic Quadratic (MCQ) equation performed better. In 200 diabetic subjects with a wide range of renal function, GFR was measured by 51Cr-EDTA clearance, and compared with the results of the three predictive equations by regression analysis and Bland and Altman procedures. The correlations with body mass index, age and albumin excretion rates were tested. The precisions (absolute difference as percentage), diagnostic accuracies [receiver operating characteristic (ROC) curves for the diagnosis of moderate and severe chronic kidney disease (CKD)], and the results of stratification according to the KDOQ classification were compared. The CG and MCQ overestimated mean GFR, whereas the MDRD underestimated it. Correlation coefficients and areas under the ROC curves were better for the MDRD and the MCQ as compared with the CG, which was biased by body weight (+30% overestimation in obese diabetic subjects). The absolute differences with true GFR were slightly lower for the MDRD than the MCQ, and both better than the CG. Both the MDRD and MCQ correctly stratified 65% of the subjects (CG: 55%, P<0.05). In contrast with the MDRD, the MCQ did not underestimate normal GFR, and its performance for stratification was uniformly good over a wide GFR range. In diabetic subjects, the MCQ has a similar diagnostic performance to the MDRD, but it does not underestimate normal GFR, which is an important advantage.

Prevalence of decreased glomerular filtration rate in patients seeking non-nephrological medical care — An evaluation using IDMS-traceable creatinine based MDRD as well as Mayo Clinic quadratic equation estimates

Background Data on the prevalence of decreased glomerular filtration rate in Europe are limited. Most of the available studies did not employ laboratory methods providing creatinine concentrations traceable to the reference method, i.e. isotope dilution mass spectrometry (IDMS). Methods We therefore conducted a cross-sectional study in the principality of Liechtenstein consecutively enrolling adult patients seeking non-nephrological medical care from whom serum samples were referred for renal function assessment. All measurements were done in one central laboratory. The estimated glomerular filtration rate (eGFR) was calculated based on the determination of IDMS-traceable creatinine by a kinetic Jaffe method (Roche Diagnostics, Switzerland) by means of the MDRD and Mayo Clinic quadratic equations. We further estimated the incidence of end stage renal disease during the next 5 years. Results For 43% ( n = 9378) of the entire population ≥ 25 years renal function assessment was available. An eGFR indicating chronic kidney disease (CKD) stages 3–5 was found in 4.93% when using the MDRD equation and in 3.98 % when using the Mayo Clinic quadratic equation. The two equations had a very good agreement in classifying patients to have an eGFR consistent with CKD stages 3–5 (Cohen's kappa 0.887). Further calculations suggested that among patients aged 80 or younger, annually 42 per 100,000 are going to develop an eGFR < 15 ml/min/1.73 m 2 over the next 5 years. Conclusions 4–5% of patients seeking non-nephrological medical advice have an eGFR consistent with CKD stages 3–5, and a considerable number of subjects is expected to develop end stage renal disease over a 5 year period. In order to obtain comparable kidney function estimates among different institutions it is not only important to use standardized methods to measure creatinine but rather to employ standardized methods to calculate a GFR estimate.