Visual inspection with acetic acid (VIA) for cervical screening

What it measures. Dilute (three to five per cent) acetic acid makes abnormal cervical epithelium, dense with protein, turn opaque white for a minute or two while normal tissue stays pink. A trained nurse or health worker inspects with a bright light and classifies the cervix as negative, positive or suspicious for cancer. Lugol's iodine (VILI) is a variant. The test gives an answer while the woman is still on the couch, which is its whole point: eligible positives can be treated at once by cryotherapy or thermal ablation without a second visit that many women in rural settings never make.

Evidence. Cluster-randomised trials in India provide the evidence. In Dindigul district (Lancet 2007) a single round of VIA screen-and-treat in women aged 30 to 59 reduced cervical cancer incidence by a quarter and mortality by about a third over seven years. The Mumbai trial run by the Tata Memorial Centre, screening every two years with primary health workers, showed a 31 per cent fall in cervical cancer mortality after twelve years. The Osmanabad trial compared VIA, cytology and HPV testing head to head; only HPV testing reduced advanced cancers and deaths in a single round, which is why the World Health Organization now prefers HPV testing as the primary test, with VIA as a triage of HPV-positive women or as the primary test where HPV testing is not yet affordable.