. 2023 Jun 28;9(2):e12404. doi: 10.1002/trc2.12404

TABLE 2.

Parameter estimates for plasma biomarker models.

	Plasma p‐tau 217 model	Plasma GFAP model
K_in (U/mL/h)	0.000372 (0.000247, 0.000613)	0.000355 (0.000237, 0.000584)	0.0017 (0.00103, 0.00259)	0.00179 (0.00099, 0.00250)
Baseline p‐tau217 concentration (U/mL)	0.389 (0.376, 0.403)	0.384 (0.372, 0.396)	‐	‐
Baseline GFAP concentration (U/mL)	‐	‐	201 (188.4, 212.2)	201 (193.3, 212.0)
Effect of amyloid reduction on K_in	0.273 (0.236, 0.315)	0.274 (0.231, 0.319)	–1.17 (–2.113, –0.673)	–1.17 (–2.31, –0.75)

Plasma p‐tau 217 model

Plasma GFAP model

Parameter

Base model

Population mean

(95% CI) ^a

Final model

Population mean

(95% CI) ^a

Base model

Population mean

(95% CI) ^a

Final model

Population mean

(95% CI) ^a

K_in (U/mL/h)

0.000372

(0.000247, 0.000613)

0.000355

(0.000237, 0.000584)

0.0017

(0.00103, 0.00259)

0.00179

(0.00099, 0.00250)

Baseline p‐tau217 concentration (U/mL)

0.389

(0.376, 0.403)

0.384

(0.372, 0.396)

‐

Baseline GFAP concentration (U/mL)

‐

201

(188.4, 212.2)

201

(193.3, 212.0)

Effect of amyloid reduction on K_in

0.273

(0.236, 0.315)

0.274

(0.231, 0.319)

–1.17

(–2.113, –0.673)

–1.17

(–2.31, –0.75)

Covariate effect on baseline plasma concentration
Effect of baseline tau PET SUVR ^b	‐	0.966 (0.671, 1.27)	‐	‐
Effect of baseline age ^c	‐	‐	‐	0.0180 (0.0106, 0.0251)
Effect of baseline weight ^d	‐	‐	‐	–0.50 (–0.70, –0.294)

Covariate effect on baseline plasma concentration

Effect of baseline tau PET SUVR ^b

‐

0.966

(0.671, 1.27)

‐

Effect of baseline age ^c

‐

0.0180

(0.0106, 0.0251)

Effect of baseline weight ^d

‐

–0.50

(–0.70, –0.294)

Interindividual variability CV% (95% CI) ^e
Baseline p‐tau217 concentration (U/mL)	26.0% (23.2, 28.6)	23.4% (20.6, 25.6)	‐	‐
Baseline GFAP concentration (pg/mL)	‐	‐	36.9% (33.4‐40.2)	33.7% (30.1‐38.1)
Treatment effect	39.5% (23.3, 51.2)	38.3% (21.4, 50.2)	91.9% (44.0‐151.5)	91.1% (33.3‐154.6)

Interindividual variability CV% (95% CI) ^e

Baseline p‐tau217 concentration (U/mL)

26.0%

(23.2, 28.6)

23.4%

(20.6, 25.6)

‐

Baseline GFAP concentration (pg/mL)

‐

36.9%

(33.4‐40.2)

33.7%

(30.1‐38.1)

Treatment effect

39.5%

(23.3, 51.2)

38.3%

(21.4, 50.2)

91.9%

(44.0‐151.5)

91.1%

(33.3‐154.6)

Residual unexplained variability
Proportional	18.6% (16.8, 20.5)	18.6% (16.9, 20.7)	17.9 % (16.9‐19.4)	17.9% (16.7‐19.3)

Residual unexplained variability

Proportional

18.6%

(16.8, 20.5)

18.6%

(16.9, 20.7)

17.9 %

(16.9‐19.4)

17.9%

(16.7‐19.3)

Abbreviations: BTAUSUVR, baseline tau PET SUVR; CI, confidence interval; CV, coefficient of variation; K_in, p‐tau217 synthesis input rate; PET, positron emission tomography; SUVR, standardized uptake value ratio.

^{^a}

95% CI from bootstrap.

^{^b}

Typical logit for baseline p‐tau217 concentration = 0.384* (1 + 0.966*[BTAUSUVR‐1.2]), where BTAUSUVR is baseline tau PET SUVR (mean, CV%: 1.22, 9.68%).

^{^c}

Effect of age on baseline is (1+0.0183*[age‐75]).

^{^d}

Effect of weight on entry on baseline is (WT/72.2)^–0.50.

^{^e}

Inter‐individual variability was calculated using the following equation for log‐normal distributions of the random effects $% C V = 100 \times \sqrt (e^{O M E G A_{N}} - 1)$ , or normal distribution of random effects of $% C V = 100 \times \sqrt e^{O M E G A_{N}}$ , where OMEGA_N is the variance of the parameter.