Analysing blood samples in the blink of an eye

This machine collects cattle blood which then goes onto a card. Photo: Wageningen Food Safety Research


The dried blood spot (DBS) method allows samples taken from animals to be checked quickly and easily for banned substances. The idea is that this new analysis method should become one of the major innovations in the work of the Netherlands Food and Consumer Products Safety Authority in a few years’ time. Researcher Irma Bongers and project manager Marco Blokland of Wageningen University & Research are working on improving this technique. They talk about its benefits for people and animals.

Fipronil in chicken eggs, hepatitis E in pork, fraud with horsemeat and prohibited growth hormones: if you follow the news, you will regularly hear of abuses in the food industry, mainly involving animal products. The Food and Consumer Products Safety Authority (NVWA) has inspectors who carry out checks in the food industry to prevent these and similar risks for humans and animals. An important element of these checks is analysing animal tissues (and their products) to detect the presence of substances that are banned in the European Union, such as certain antibiotics and growth hormones. The NVWA inspectors collect samples for this purpose. Depending on what they are testing, the sample may consist of urine, meat, eyeballs, hair or milk from a milk tank. Then the samples have to be analysed, which is something Wageningen Food Safety Research does.

Promising analysis method

The laboratories responsible for the analyses are currently working hard on DBS, which is seen as a promising new analysis method. Anyone who has had a baby will know exactly how it works, because it is similar to the heel prick that is carried out a few days after birth. A few droplets of blood are put on a piece of card, which can then go to the lab for testing. That is where researcher Irma Bongers starts to get enthusiastic, as DBS has numerous advantages. “Taking a urine sample is tricky because you have to wait until the animal pees,” explains Bongers, whereas you can always take a blood sample. What is more, the sample cards with the blood droplets are cheap to transport and store. “But the most important advantage is that you can automate the entire process in the lab. When the card arrives, not a single human has to handle it. That saves a lot of time.”

Livestock in the Netherlands undergoes preventive testing for banned substances and antibiotics. WUR researcher Irma Bongers is experimenting with the dried blood spot method, which makes taking blood samples easy and efficient. It’s a painless technique for cattle and pigs, comparable with the finger prick test.

The traditional methods are very different in that respect, explains Bongers. “With urine and meat samples, an analyst has to spend a full day in the lab adding chemicals until the sample can finally enter the system.” First you need to perform an extraction, a process similar to brewing tea, to get the substances you are looking for. Then you have to clean up the solution. The awkward aspect is that each substance that you want to detect has different properties and reacts differently to the extraction and clean-up. “We test for the presence of 200 to 300 substances, from specific antibiotics to banned hormones. You need different techniques with different solvents for each substance. That makes it impossible to test for all those substances in one go.”

Detecting a hundred substances

They are increasingly close to being able to implement DBS because improvements keep being made to the detection technique used to analyse the samples. “Conventional analyses require material in gram and millilitre quantities,” explains Bongers. “That lets you create concentrated samples with levels of substances that are above the limit of detection. With the dried spot method, you only need a small droplet of about 10 microlitres. Fifteen years ago, the techniques weren’t good enough to detect substances in such small amounts, but we have now demonstrated that you can still detect very low levels of the substances you are looking for in such a small amount of blood.” Even so, DBS needs a lot of work before it can actually become the standard method in use at Wageningen’s laboratories. “We can currently detect nearly 100 substances using DBS.”

It’s just so easy: I send you a card, you add the spot to it and send the card back

Bongers and her colleagues have been developing and validating more and more methods using this technique, for example to detect steroid esters (banned growth promotors) and nitroimidazoles (antibacterial compounds that are now known to be toxic). They are also working hard on a method for revealing beta-agonists, substances that are banned here — although permitted under some circumstances in the United States — and that influence the ratio of fat to meat.

Machines for blood collection of cows. Photo: Wageningen Food Safety Research

The machine collects blood through micro needless almost painlessly, which reduces stress significantly. Photo: Wageningen Food Safety Research

But however promising DBS might sound, it also has its disadvantages, explains project manager Marco Blokland. “We want to be able to take a blood sample without hurting the animal, so you can’t just put a needle in a vein. With people, you can ask them to stick out their finger so you can take a droplet of blood. You can’t do that with an animal.” Bongers explains that this is why they are using a medical device that was developed in the United States. “It is a little box with micro-needles and a strip of adhesive. You place it on the cow’s hide, press a button and the tiny needles shoot through the surface of the skin. Because the box applies suction, blood is slowly drawn into the reservoir. This is aimed at minimising the stress for the cow.”

Olympic Games

There is still work to be done too in letting the sector get accustomed to this new method. “A change like this takes time. We try to get everyone in the supply chain on board. At the same time, we make sure the methods work properly and show that it is technically feasible.” That is why Blokland organised online workshops over the past year with inspectors and other stakeholders to introduce the method and discuss it. “We demonstrated taking the blood sample and analysing dried blood spots and explained the benefits of this technique through short videos.” This approach seems to be bearing fruit. Inspectors see for themselves that DBS will let them work more effectively and they are enthusiastically joining the discussion on what is possible and what isn’t. The Dutch government also sees DBS as an interesting option that has benefits for the entire supply chain.

The card onto which blood or other liquids are applied. Photo: Wageningen Food Safety Research

The dried blood spot system is linked to automatic clean up and detection systems. Photo: Wageningen Food Safety Research

There are also the more long-term speculations on what the DBS method can achieve. As Blokland says, it is not just applicable to blood. “You can make spots from any fluid, so that could mean milk.” He also sees use of DBS taking off in the clinical sector, with people rather than animals. “It is just so easy: I send you a card, you add the spot to it and send the card back. That is a huge advance as you no longer have to go to the hospital and it doesn’t cost much effort.” Even the world of sports has its eye on the technique, says Bongers. “The World Anti-Doping Agency is looking at whether it could use dried blood spots. They hope they will be able to implement it further by the next Olympic Games.”

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