The tuberculin skin test: a comparison of ruler and calliper readings.
BACKGROUND
The Mantoux tuberculin skin test (TST) is widely used to diagnose latent infection with Mycobacterium tuberculosis. TST skin induration may be measured either by a transparent ruler or by a pair of callipers. We hypothesised that the type of instrument used may affect the reading.


OBJECTIVE
To determine whether variability in Mantoux TST measurement is affected by the type of reading instrument.


METHODS
A TST (Mantoux method) was performed among healthy adolescents. The indurations were read with among ruler and calliper by two independent readers. Limits of agreement and Kappa (κ) scores at TST positivity cut-off points were calculated. A Bland-Altman graph was constructed.


RESULTS
The 95% limits of agreement between instruments ranged from -5 mm to 3 mm. The limits of agreement between readers ranged from -5 mm to 4 mm. κ scores between instruments were respectively 0.7 and 0.8 at 15 mm and 10 mm cut-offs.


CONCLUSIONS
The variability between readers of TST indurations is not influenced by changing the reading instrument.
Geldenhuys
H
H
South African Tuberculosis Vaccine Initiative, University of Cape Town, Cape Town, South Africa. hennie.geldenhuys@uct.ac.za
Verver
S
S
Surtie
S
S
Hatherill
M
M
van Leth
F
F
Kafaar
F
F
Tameris
M
M
Kleynhans
W
W
Luabeya
K K
KK
Moyo
S
S
Sikhondze
W
W
Hanekom
W
W
Mahomed
H
H
D000293:Adolescent; D002648:Child; D003430:Cross-Sectional Studies; D004867:Equipment Design; D006801:Humans; D055985:Latent Tuberculosis / Q000175:diagnosis* / Q000382:microbiology; D009169:Mycobacterium tuberculosis / Q000472:pathogenicity*; D015588:Observer Variation; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D014374:Tuberculin Test / Q000295:instrumentation* / Q000592:standards