Study objectives: To assess the validity of purified
protein derivative (PPD) readings by patients and trained health-care
professionals as compared with a calibrated model.
and participants: Survey of a group of patients, nurses, medical
assistants, and physicians at five neighborhood health centers in the
Interventions: Participants were asked to
read a calibrated model with four PPD indurations measuring 0 mm, 3 mm,
7 mm, and 13 mm. Indurations ≥ 5 mm were to be considered“
Measurements and results:
Data were obtained from 233 patients and 80 trained professionals. All
patients correctly measured the 0-mm induration site and were able to
detect the presence of an induration in 99.3% of possible
observations. Compared with professionals, patients had more
variability in measurements and interpretations of the 3-, 7-, and
13-mm sites. Professionals detected 100% of all indurations.
Patients’ specificity for the 0- and 3-mm sites was 97.4% and 62.7%,
respectively; whereas sensitivity for the 7- and 13-mm sites was 68.2%
and 89.3%, respectively. Professionals’ specificity for the 0- and
3-mm sites was 98.7% and 65.3%, respectively; their sensitivity for
the 7- and 13-mm sites was 86.7% and 97.3%, respectively. Seventy
percent of professionals agreed that the model was a realistic
representation of PPD indurations.
Patients can reliably distinguish between the presence and absence of
an induration at a PPD injection site. They are not as reliable in the
measurement and interpretation of test reactions. Professionals had
considerable variability in their assessments of PPDs but were more
precise overall in their assessments than patients.