Estimation of total kidney volume in autosomal dominant polycystic kidney disease

Abstract

Background: In autosomal dominant polycystic kidney disease (ADPKD), obtaining measured total kidney volume (mTKV) by magnetic resonance (MR) imaging and manual tracing is time consuming. Two alternative MR imaging methods have recently been proposed to estimate TKV (eTKVellipsoid and eTKVPANK), which require less time.

Study design: Cross-sectional and longitudinal diagnostic test study.

Setting & participants: Patients with ADPKD with a wide range of kidney function and an approved T2-weighted MR image obtained at the University Medical Centers of Groningen, Leiden, Nijmegen, and Rotterdam, the Netherlands, in 2007 to 2014. Test set for assessing reproducibility, n=10; cohort for cross-sectional analyses, n=220; and cohort for longitudinal analyses, n=48.

Index tests: Average times for eTKVellipsoid and eTKVPANK were 5 and 15 minutes, respectively. Bias is defined as (mTKV - eTKV)/mTKV × 100%; precision, as one standard deviation of bias.

Reference tests: mTKV using manual tracing to calculate the area within kidney boundaries times slice thickness. Average time for mTKV was 55 minutes.

Results: In the test set, intra- and intercoefficients of variation for mTKV, eTKVellipsoid, and eTKVPANK were 1.8% and 2.3%, 3.9% and 6.3%, and 3.0% and 3.4%, respectively. In cross-sectional analysis, baseline mTKV, eTKVellipsoid, and eTKVPANK were 1.96 (IQR, 1.28-2.82), 1.93 (IQR, 1.25-2.82), and 1.81 (IQR, 1.17-2.62) L, respectively. In cross-sectional analysis, bias was 0.02% ± 3.2%, 1.4% ± 9.2%, and 4.6% ± 7.6% for repeat mTKV, eTKVellipsoid, and eTKVPANK, respectively. In longitudinal analysis, no significant differences were observed between percentage change in mTKV (16.7% ± 17.1%) and percentage change in eTKVellipsoid (19.3% ± 16.1%) and eTKVPANK (17.8% ± 16.1%) over 3 years.

Limitations: Results for follow-up data should be interpreted with caution because of the limited number of patients.

Conclusions: Both methods for eTKV perform relatively well compared to mTKV and can detect change in TKV over time. Because eTKVellipsoid requires less time than eTKVPANK, we suggest that this method may be preferable in clinical care.

Keywords: Autosomal dominant polycystic kidney disease (ADPKD); PANK; ellipsoid; estimation methods; magnetic resonance imaging (MRI); total kidney volume (TKV); validation.