Typically, clinicians rely on either self-report by patients, pill counts or expensive medication dispensing devices to monitor how well patients are taking their pills as directed. These methods are highly patient dependent.

Now, a US team, led by Indian-origin scientist Monica Gandhi, has found that the levels of antiretrovirals in hair of patients on treatment correlated strongly with levels of HIV virus circulating in patients' blood, the 'AIDS' journal reported in its latest edition.

"Clinicians can draw blood and then measure plasma levels of medications, but since a single plasma level represents medication exposure hours prior to the blood draw, this method hasn't been a good predictor of viral suppression.

"High levels of antiretrovirals in hair correlated with success in HIV viral suppression in treatment and did so better than any of the other variables usually considered to predict response," Gandhi of California University said.

In fact, according to the scientists, hair, which grows at a rate of about a centimetre a month, gives a reading of drug levels which reflects the rate of pill consumption sustained by patients over weeks, not days.

Assessing an average level of drug exposure over time may be more predictive of treatment response than the "snapshot" of exposure provided by a single plasma level of medication, Gandhi said.

Added co-scientist Ruth M. Greenblatt "Hair sampling for antiretroviral levels could become a new standard to look at how much drug a patient is getting – an equivalent in HIV clinical care of measuring haemoglobin A1C, the method used in diabetes to monitor average blood glucose levels."

In their study, the scientists took 10 strands of hair from patients on HIV therapy from the back of the head. They cut the hair sample close to the scalp underneath the top layer of hair, marked the part farthest from the scalp with tape and wrapped the strands in aluminium foil. The sample was stored at room temperature in plastic bag till its analysis.

"This is a painless, bloodless, biohazard-free, method of collecting a stable specimen from HIV patients that may allow for the monitoring of levels of antiretroviral drugs absorbed over time and the prediction of treatment success.

"Our next step is to test this method in resource-limited settings where blood collection and viral load monitoring may be expensive and difficult.