Table 4. Pharmacokinetic and non-pharmacokinetic adherence measures among five participants who had at least one sample with undetectable drug in the US CDC PrEP safety study.

	Detectable tenofovir in biological measures of drug exposure					Count data for non-biological measures of drug exposure					Most likely Interpretation
Participant	Hair (level ng/mg hair)	Plasma on hair collection date (ng/mL)	Plasma on PBMC collection date (ng/mL)	PBMC on hair collection date (fmol/sample)	PBMC if done on date other than hair	MEMS openings 90 days before hair (%)	MEMS openings 90 days before PBMC (%)	Self-report by ACASI using VAS (%)	Pill counts in 90 days before hair	Pill counts in 90 days before PBMC	-
1	Yes (0.026)	Yes (48.3)	PBMCs, plasma and hair collected on same date	No (BLQ)	n/a	92.2	92.2	90	95.5	95.5	False negative PBMC result or remote dosing (suggested by hair) with dosing holiday (PBMC BLQ) and then very recent dosing before clinic visit (plasma elevated)
2	Yes (0.042)	Yes (99.5)	No (BLQ)	n/a	No (BLQ) (58 days before hair)	68.9	1.1	100	73.3	N/A	Low/no adherence before PBMC collection date, but higher adherence before hair collection date
3	Yes (0.069)	Yes (446)	No (BLQ)	n/a	Yes (52.48 fmol/sample, 103 days after hair)	34.4	31.1	90	86.0	38.8	Adherence throughout the duration with waning adherence in the last few days prior to PBMC sampling, or false negative plasma test.
4	No (BLQ)	Yes (188)	Yes (87.4)	n/a	Yes (43.62 fmol/sample, 91 days after hair)	42.2	75.6	90	82.4	80.2	False negative hair result, or, less likely, recent adherence without remote adherence.
5	Yes (0.011)	No (BLQ)	No (BLQ)	n/a	No (BLQ) (32 days after hair)	0	0	70	1.6	21.9	Remote adherence without recent adherence.

PBMC = peripheral blood mononuclear cells, MEMS = medication electronic monitoring system; ACASI = audio computer-assisted self-interview; VAS = visual analog scale; BLQ = below lower limit of quantification