Abstract
BackgroundUsing serum creatinine leads to an overestimation of kidney function in patients with primary neuromuscular disorders, and reduced kidney function may remain undetected. Cystatin C (CysC) could provide a better estimation.AimTo evaluate the precision, accuracy, and bias of two creatinine-, one cystatin C-based and one combined equation to estimate glomerular filtration rate (eGFR) in patients with primary neuromuscular disease.Patients and methodsOf the 418 patients initially identified at the out-patient clinic, data on kidney function was obtained for 145 adult patients (age 46 ± 14 years, BMI 26 ± 6 kg/m2) with primary neuromuscular disease. Kidney function was measured by iohexol clearance, and blood samples for serum creatinine and CysC were drawn simultaneously. Bias was defined as the mean difference between eGFR and measured iohexol clearance, and accuracy as the proportion of eGFRs within ± 10% (P10) of measured clearance.ResultsKidney function (iohexol clearance) was 81 ± 19 (38–134) ml/min/1.73m2. All equations overestimated kidney function by 22–60 ml/min/1.73m2. eGFR CysC had the lowest bias overall 22 (95% CI 20–26) ml/min/1.73m2 also at all levels of kidney function we evaluated (at 30–59 ml/min/1.73m2 bias was 27 (95% CI 21–35), at 60–89 it was 25 (95% CI 20–28) and at ≥ 90 it was 12 (95% CI 7–22)). eGFR CysC also had the best accuracy in patients with reduced kidney function (P10 was 5.9% at 30–59 ml/min/1.73m2).ConclusionsCystatin C-based estimations of kidney function performed better than creatinine-based ones in patients with primary neuromuscular disease, but most importantly, all evaluated equations overestimated kidney function, especially in patients with reduced kidney function. Therefore, kidney function should be measured by gold-standard methods when precision and accuracy are needed.Graphic abstract
Highlights
Glomerular filtration rate (GFR) is a validated marker of kidney function [1, 2] recommended in treatment guidelines [3, 4]
Cystatin C (CysC) has been evaluated in different patient populations, but few studies have assessed CysC in patients with primary neuromuscular diseases including Duchenne muscular dystrophy (DMD) [13, 14], amyotrophic lateral sclerosis (ALS) [15] and myotonic dystrophy type 1 (DM1) [16]
All estimate glomerular filtration rate (eGFR) correlated to measured clearance (ρ = 0.41–0.64) and the strongest correlation was found between the cystatin C-based eGFR (ρ = 0.64) followed by the combined cystatin C- and creatinine–based eGFR (ρ = 0.61) and the creatinine-based eGFR (CKD-EPI) (ρ = 0.48)
Summary
Glomerular filtration rate (GFR) is a validated marker of kidney function [1, 2] recommended in treatment guidelines [3, 4]. Male gender, body mass index (BMI), fat mass, triglycerides, hypertension, uric acid, C-reactive protein and diabetes have all been associated with higher serum concentrations of CysC regardless of kidney function [12, 17] This is of importance since patients with muscular dystrophy often have an absolute or relative increase in body fat [18, 19]. Aim To evaluate the precision, accuracy, and bias of two creatinine-, one cystatin C-based and one combined equation to estimate glomerular filtration rate (eGFR) in patients with primary neuromuscular disease. Conclusions Cystatin C-based estimations of kidney function performed better than creatinine-based ones in patients with primary neuromuscular disease, but most importantly, all evaluated equations overestimated kidney function, especially in patients with reduced kidney function. Kidney function should be measured by gold-standard methods when precision and accuracy are needed
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