TABLE 7.

Formulas to calculate full and abbreviated iBOX scores.

	$iBo{x}_i={\displaystyle {\sum }_{j=1}}\widehat{{\mathit{b}}_j}{\mathit{x}}_{i,j}$ for subject i where	Full iBOX	Abbreviated iBOX
	Factor	HR (exp $\left.{\left[\widehat{\beta }\right.}_j]\right)$ (95% CI) a
${\mathit{X}}_{\mathit{i},\mathbf{1}}$	Time from transplant to evaluation (y)	1.08 (1.03–1.14)	1.12 (1.07–1.18)
${\mathit{X}}_{\mathit{i},\mathbf{2}}$	eGFR (mL/min/1.73 m2)	0.96 (0.95–0.96)	0.95 (0.95–0.96)
${\mathit{X}}_{\mathit{i},\mathbf{3}}$	Log transformed UPCR proteinuria (g/g)	1.5 (1.39–1.62)	1.59 (1.48–1.71)
${\mathit{X}}_{\mathit{i},\mathbf{4}}$	Anti-HLA DSA MFI
	<1,400	1	1
	≥1,400	1.84 (1.44–2.34)	1.84 (1.44–2.34)
${\mathit{X}}_{\mathit{i},\mathbf{5}}$	Interstitial fibrosis/tubular atrophy (IFTA score)		N/A
	0–1	1
	2	1.14 (0.92–1.43)
	3	1.41 (1.1–1.8)
${\mathit{X}}_{\mathit{i},\mathbf{6}}$	Microcirculation inflammation (g score and ptc score)
	0–2	1
	3–4	1.43 (1.11–1.85)
	5–6	1.84 (1.25–2.7)
${\mathit{X}}_{\mathit{i},\mathbf{7}}$	Interstitial inflammation and tubulitis (i score and t score)
	0–2	1
	≥3	1.33 (1.06–1.68)
${\mathit{X}}_{\mathit{i},\mathbf{8}}$	Transplant glomerulopathy (cg score)
	0	1
	≥1	1.47 (1.14–1.9)

CI, confidence interval; DSA, donor-specific antibody; HLA, human leukocyte antigen; HR, hazard ratio; MFI, mean fluorescence intensity; N/A, not applicable.

^a ${\widehat{\beta }}_j$ = the log of the HR values.

For categorical variables with more than 2 levels, e.g., IFTA score, the contribution of the variables was calculated as follows: β₁x₁ + β ₂x₂. If the IFTA score = 0 or 1, then x₁ = 0 and x₂ = 0. If the IFTA score = 2, then x₁ = 1 and x₂ = 0. If the IFTA score = 3, then x₁ = 0 and x₂ = 1. β₁ and β₂ refer to the beta coefficients for the IFTA scores = 2 and 3, respectively.