Measurement Matters: A Metrological Approach to Renal Preimplantation Biopsy Evaluation to Address Uncertainty in Organ Selection

Abstract

Background: Preimplantation biopsy combines measurements of injury into a composite index to inform organ acceptance. The uncertainty in these measurements remains poorly characterized, raising concerns variability may contribute to inappropriate clinical decisions.

Methods: We adopted a metrological approach to evaluate biopsy score reliability. Variability was assessed by performing repeat biopsies (n = 293) on discarded allografts (n = 16) using 3 methods (core, punch, and wedge). Uncertainty was quantified using a bootstrapping analysis. Observer effects were controlled by semi-blinded scoring, and the findings were validated by comparison with standard glass evaluation.

Results: The surgical method strongly determined the size (core biopsy area 9.04 mm², wedge 37.9 mm²) and, therefore, yield (glomerular yield r = 0.94, arterial r = 0.62) of each biopsy. Core biopsies yielded inadequate slides most frequently. Repeat biopsy of the same kidney led to marked variation in biopsy scores. In 10 of 16 cases, scores were contradictory, crossing at least 1 decision boundary (ie, to transplant or to discard). Bootstrapping demonstrated significant uncertainty associated with single-slide assessment; however, scores were similar for paired kidneys from the same donor.

Conclusions: Our investigation highlights the risks of relying on single-slide assessment to quantify organ injury. Biopsy evaluation is subject to uncertainty, meaning each slide is better conceptualized as providing an estimate of the kidney's condition rather than a definitive result. Pooling multiple assessments could improve the reliability of biopsy analysis, enhancing confidence. Where histological quantification is necessary, clinicians should seek to develop new protocols using more tissue and consider automated methods to assist pathologists in delivering analysis within clinical time frames.

Graphical abstract

FIGURE 1.

Sample processing and analysis in unblinded and semi-blinded conditions. This flowchart depicts the progression of samples from collection to analysis. For both methods, 12 patients provided 16 kidneys, from which 144 biopsies were produced and 2 HE and PAS glass slides were generated. In the unblinded scenario, slides were examined jointly, and a single Remuzzi score was reported for each biopsy. In the semi-blinded scenario, slides were assessed individually. HE, hematoxylin and eosin; PAS, periodic acid–Schiff.

FIGURE 2.

Scatter plots analyzing core (green cross), punch (orange circle), and wedge (purple star) biopsies. A, Physical profile (n = 250), core biopsies are long and thin, with wedge biopsies having the reverse profile. Punch biopsies are the most consistent. B and C, Glomerular yield (n = 250, r = 0.94) and arterial yield (n = 249, r = 0.62) retrieved and the size of each sample. D, Relationship between the number of glomeruli in the sample and the percentage of glomerulosclerosis. The background color reflects the Remuzzi score (0 = blue, 1 = green, 2 = orange, 3 = red). Glomerulosclerosis is weakly correlated with the size of the sample (Spearman’s rank coefficient r = 0.13, P = 0.03).

FIGURE 3.

Distribution of Remuzzi scores for each kidney, with each column representing a single kidney (eg, PL1 = donor 1, left kidney). Shading illustrates the decision to transplant singly (1–4, white), as a dual (>4–6, gray), or discard (≥7, red). Markers indicate the type of biopsy performed: green cross for core, orange circle for punch, and purple star for wedge biopsy. Noticeable variation is present within kidney groups, and pairs of kidneys (eg, PL2 and PR2) exhibit similar score distributions.

FIGURE 4.

Violin plot representing the bootstrapped (n = 1000) distribution of Remuzzi score sample means for each kidney. The plot presents the spread and density estimation of the simulated means. Shading illustrates the decision to transplant singly (1–4, white), as a dual (>4–6, gray), or discard (≥7, red). Bootstrapped means distributions show a tighter range as well as high similarity distribution within pairs, whereas distributions from other donors are generally less alike.

FIGURE 5.

Distribution of unblinded (glass slide) Remuzzi scores for each kidney, with each column representing a single kidney (eg, PL1 = patient 1, left kidney). Shading describes the decision to transplant singly (1–4, white), as a dual (>4–6, gray), or discard (≥7, red).

FIGURE 6.

Box plots that show the measured degree of injury on the y-axis for each slide scored by the pathologist (n = 265). Glomerulosclerosis = upper, IFTA = lower. The perfect agreement would show increasing, nonoverlapping groups, which are separable at the Remuzzi threshold for each component (gray boundaries 0–3). IFTA, interstitial fibrosis and tubular atrophy.