An external validation of a novel predictive algorithm for male nipple areolar positioning: an improvement to current practice through a multicenter endeavor

Figures & data

Table 1. Demographic and anatomic measurements.

Demographic data	Age (y)
Weight (kg)	Height (m)
Measurements	Sternal notch to nipple (SNN) (cm) – mean-value
	Nipple-nipple distance (NN) (cm)
	Chest circumference (CC) (cm)
	Anterior axillary fold to anterior axillary fold (AUX–AUX) (cm)

Figure 1. A depiction of how to apply the algorithm in the clinical setting. Previously presented in the primary study [17].

Table 2. Demographic data, measurement outcomes and comparison of the (cisgender male) validation cohort to the (cisgender male) primary cohort.

	Validation cohort (UZG, BE) N = 51	Primary cohort (Amsterdam UMC, NL) N = 150	p-Value
Age (years) (median – IQR)	31.0 (27.0–36.0)	26 (22.0–34.3)	<0.001*
Weight (kg) (mean –SD)	79.5 (10.5)	79.8 (10.3)	0.751**
Height (cm) (mean –SD)	181.2 (6.7)	182.9 (6.7)	0.138**
BMI (kg/m2) (mean –SD)	24.2 (3.0)	23.7 (3.0)	0.511**
Inter-nipple distance (NN) (cm) (mean –SD)	23.4 (1.9)	22.9 (2.0)	0.127**
Sternal-notch to nipple distance (SNN) (cm) (mean –SD)	19.9 (1.8)	19.9 (1.7)	0.474**
Chest circumference (CC) (cm) (mean –SD)	94.2 (8.6)	93.5 (8)	0.612**
Anterior-axillary fold to anterior-axillary fold (AUX-AUX) (cm) (mean –SD)	40.3 (4.1)	40.7 (3.9)	0.408**

*Mann–Whitney U test; **independent t-test.

Table 3. External validation of the NN-algorithm and utility comparison to other comparable NN-algorithms.

Measure	Author(s)	Algorithm	MSE (95% CI)	MAPE (%) (95% CI)	R^2
NN	This study (external validation cohort)	4.11 + (0.035 * age + 0.041 * weight + 0.093 * CC + 0.14 * AUX–AUX)	2.35	4.9	0.315
			(0–6.9)	(3.8–6.1)
	Timmermans et al. (primary cohort) (Timmermans et al., 2021)	4.11 + (0.035 * age + 0.041 * weight + 0.093 * CC + 0.14 * AUX–AUX)	1.37	4.1	0.650
			(1.08–1.68)	(3.6–4.6)
	Beer et al. (Beer et al., 2001)	2 * (2.4 + 0.09 * CC)	5.34	8.4	−0.552
			(0–10.95)	(7.2–6.9)
	Shulman et al.(Shulman et al., 2001)	2.192 + (0.19 * CC)	13.7	14.6	−0.300
			(4.33–23.19)	(13.3–15.9)

MSE: mean square error; MAPE: mean absolute percentage error.

Table 4. External validation of the SNN-algorithm and utility comparison to comparable SNN-algorithms.

Measure	Author(s)	Algorithm	MSE (95% CI)	MAPE (%) (95% CI)	R^2
SNN	This study (external validation cohort)	7.248 + (0.303 * NN + 0.072 * weight)	1.51 (0–4.02)	4.73 (3.7–5.7)	0.423
	Timmermans et al. (primary cohort) (Timmermans et al., 2021)	7.248 + (0.303 * NN + 0.072 * weight)	1.43 (1.13–1.74)	4.7% (4.1–5.3)	0.510
	Shulman et al.(Shulman et al., 2001)	(0.12 * height) – 2.782	4.06 (0–12.71)	7.19 (5.6–8.8)	−0.524
	Beckenstein et al.(Beckenstein et al., 1996)	11.1 + (0.13 * height in inches)	2.60 (0–7.06)	6.59 (5.29–7.89)	0.025

MSE: mean square error; MAPE: mean absolute percentage error.

Table 5. Site comparison of NAC positioning in transgender individuals based on standard practice.

	Center 1 (UZG, BE) (n = 25) Mean, median (SD, IQR)			Center 2 (Amsterdam UMC, NL) (n = 96) Mean, median (SD, IQR)			p-Value
Age	24.0 (20.5–28.5)			21.0 (19.0 − 25.0)			0.054*
Age (year)	69.6 (12.3)			68.2 (13.5)			0.627**
Weight (kg)	88.8 (8.0)			86.3 (9.7)			0.234**
CC (cm)	35.8 (3.1)			35.5 (3.3)			0.714**
NN (cm)	Measured	Predicted	p-Value	Measured	Predicted	p-Value
	22.0 (2.6)	21.2 (1.6)	0.025***	19.8 (2.2)	20.7 (1.9)	<0.001***
Mean difference	0.8 (1.7)			−0.9 (1.7)			<0.001**
SNN (cm)	Measured	Predicted	p-Value	Measured	Predicted	p-Value
	17.1 (1.7)	18.7 (1.4)	<0.001***	16.2 (1.8)	18.4 (1.5)	<0.001***
Mean difference	−1.6 (1.1)			−2.3 (1.8)			0.067**

Mann–Whitney U test*; independent t-test**; paired t-test***.

Timmermans FW, Jansen BAM, Mokken SE, et al. The ideal location of the male nipple-areolar complex: a pinpointing algorithm. Int J Transgender Health. 2021; 22(4):403–411.

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