Limited Performance of Estimated Total Kidney Volume for Follow-up of ADPKD

Abstract

Introduction: Total kidney volume (TKV) is a qualified biomarker for disease progression in autosomal dominant polycystic kidney disease (ADPKD). Recent studies suggest that TKV estimated using ellipsoid formula correlates well with TKV measured by manual planimetry (gold standard). We investigated whether the ellipsoid formula could replace manual planimetry for follow-up of ADPKD patients.

Methods: Abdominal magnetic resonance images of patients with ADPKD performed between January 1, 2013, and June 31, 2019, in Saint-Luc Hospital, Brussels, were used. Two radiologists independently performed manual TKV (mTKV) measures and kidney axial measures necessary for estimating TKV (eTKV) using ellipsoid equation. Repeatability and reproducibility of axial measures, mTKV and eTKV, and agreement between mTKV and eTKV were assessed (Bland-Altman). Intraclass correlation coefficient (ICC) was used to assess agreement on Mayo Clinic Imaging Classification (MCIC) scores.

Results: 140 patients were included with mean age 45±13 years, estimated glomerular filtration rate (eGFR) 71±31 ml/min per 1.73 m², and mTKV 1697±1538 ml. Repeatability and reproducibility were superior for mTKV versus eTKV (repeatability coefficient 2.4% vs. 14% in senior reader, and reproducibility coefficient 6.7% vs. 15%). Intertechnique reproducibility coefficient (95% confidence interval [CI]) was 19% (17%, 21%) in senior reader. Intertechnique agreement on derived MCIC scores was very good (ICC = 0.924 [0.884, 0.949]).

Conclusion: TKV estimated using ellipsoid equation demonstrates poor repeatability and reproducibility compared with that of mTKV. Intertechnique agreement is also limited, even when measurements are performed by an experienced radiologist. Estimated TKV, however, accurately determines MCIC score.

Keywords: ADPKD; TKV; ellipsoid equation; manual planimetry.

Graphical abstract

Figure 1

Study flow chart.

Figure 2

Total kidney volume distribution according to age in the total cohort (n = 140).

Figure 3

Bland-Altman plots showing repeatability of axial measures, estimated TKV (eTKV) and measured TKV (mTKV) when performed by senior radiologist. Length (L), transverse diameter (T) (width), and anterior-posterior diameter (A-P) (depth) are expressed in millimeters, whereas eTKV is expressed in milliliters. The mean bias (orange solid line), regression line of differences (red dotted line), and limits of agreement (green dotted lines) with 95% CIs (green whiskers) are represented.

Figure 4

Bland-Altman plots for the agreement between estimated TKV (eTKV) and measured TKV (mTKV) for right kidney volume (right KV), left kidney volume (left KV), and TKV, when performed by junior and senior radiologists. Paired differences are expressed as a percentage of the geometric mean to overcome potential variability in the differences across the range of mean values. The mean bias (orange solid line), regression line of differences (red dotted line), and limits of agreement (green dotted lines) with 95% CIs (green whiskers) are represented.

Figure 5

Upper limits of repeatability and reproducibility of measured TKV (mTKV) and estimated TKV (eTKV) and of agreement between mTKV and eTKV. Repeatability and agreement limits for junior radiologist (JR) are in light gray and for senior radiologist in dark gray; reproducibility limits are in black.