A drop of blood spread across a glass slide could offer important clues about a person’s health. Researchers at the Indian Institute of Technology (IIT) Bombay have developed a technique that studies how blood spreads on a glass slide to screen for severe anaemia and sickle cell disease (SCD).The research, led by Professor Mahesh S. Tirumkudulu of IIT Bombay’s Department of Chemical Engineering, was published in the journal Lab on a Chip.In a conventional blood smear test, a technician places a drop of blood on a glass slide and spreads it into a thin layer using another slide. A pathologist then examines the blood cells under a microscope. However, the thickness and spread of the sample can vary depending on how the smear is prepared.To make the process more consistent, the IIT Bombay team developed a device that holds two glass slides at a fixed angle and moves one at a controlled speed. It uses only 10 microlitres of blood. “We found that the distance blood travels on the slide is linked to its viscosity, or how easily it flows. Blood with lower haemoglobin levels, as seen in anaemia, generally flows more easily and spreads further. Blood with higher haemoglobin levels tends to spread less,” says Dr Tirumkudulu.The team has also developed a separate method that estimates haemoglobin levels by analysing the colour of the dried blood film.What did the studies find?In a study involving 516 people from tribal areas of Maharashtra, the viscosity-based method correctly identified 95.1 per cent of people with severe anaemia and 86 per cent of those without it. Severe anaemia was defined as a haemoglobin level below 8 grams per decilitre (g/dL).The separate colour-based method was tested on more than 1,000 patients from Mumbai and tribal areas of Maharashtra. It estimated haemoglobin levels within approximately 0.5 g/dL of standard laboratory measurements. The researchers also reported that it could detect haemoglobin levels as low as 2 g/dL.Story continues below this adProfessor Tirumkudulu said that giving doctors an actual haemoglobin estimate is more useful than simply reporting blood viscosity. “Knowing a patient’s haemoglobin level helps doctors decide what further care may be needed. The technique could help identify people who need further testing, particularly in areas with limited laboratory facilities,” he says.How can it screen for sickle cell disease?Sickle cell disease is an inherited condition in which abnormal haemoglobin causes red blood cells to become rigid and develop a sickle-like shape. These cells can block small blood vessels and cause serious health problems.For screening, the researchers compare how a blood sample spreads before and after adding sodium metabisulfite, a chemical that reduces oxygen in the sample. In people with sickle haemoglobin, this can make red blood cells more rigid, increasing blood thickness and changing how far it spreads.In field testing involving 394 people from tribal areas of Maharashtra, the researchers reported approximately 95 per cent correct screening results. They found that the increase in blood viscosity was generally below 17 per cent in healthy samples, between 17 and 70 per cent in people with sickle cell trait, and above 70 per cent in those with sickle cell disease.Story continues below this adThe team also explored whether the method could help track responses to hydroxyurea, a medicine used to treat sickle cell disease. In their observations, the increase in viscosity fell from around 125 per cent to 70 per cent during treatment. However, further research is needed to establish whether this can reliably monitor treatment.Importantly, the technique is a screening tool, not a definitive diagnostic test. Positive results need confirmation through laboratory testing, such as high-performance liquid chromatography (HPLC).How is it different from a dried blood spot test?A dried blood spot test involves placing a drop of blood on special absorbent paper, allowing it to dry and sending it to a laboratory. For sickle cell testing, the sample can be used for genetic analysis.The IIT Bombay technique works differently. It studies how fresh blood spreads on a glass slide and how this changes when oxygen levels are reduced. It does not directly examine DNA. The two methods, therefore, measure different things and are not interchangeable.Story continues below this adWhat will it cost, and when will it be available?The final cost of the device and each test has not been decided. However, the researchers expect the consumables to be inexpensive. An ordinary glass slide costs less than ₹1, and the chemical used for sickle cell screening is also relatively cheap.The technology has been licensed to Rheoheme Private Limited, an IIT Bombay start-up. The team has applied to the Central Drugs Standard Control Organisation (CDSCO) for a licence. Independent validation by a hospital or an Indian Council of Medical Research (ICMR) centre is still needed before commercial manufacture and sale.The device is not yet available for routine clinical use. The researchers hope it could eventually be used in hospitals and primary health centres, including in remote areas. It is also designed to transmit data to a central server, which could help health authorities understand the distribution of anaemia and sickle cell disease across districts.What are the limitations?The technique requires a precise blood sample of about 10 microlitres. Even small differences in the amount of blood used can affect the result. The team is working to make the procedure more reliable for users with limited technical training.Story continues below this adThe relationship between blood viscosity and haemoglobin may also differ across populations. The method may not work as expected in certain conditions, such as hyperviscosity syndrome, where blood is unusually thick. Larger, independent studies will be needed to establish its accuracy across different populations.The researchers are also exploring whether the approach could eventually be adapted to measure glucose, glycated haemoglobin (HbA1c), creatinine and cholesterol, or assess blood clotting time. These remain possible future applications. “The team’s initial aim was to understand the physics of spreading blood. The potential medical applications emerged from that work,” says Dr Tirumkudulu.