NEW YORK (360Dx) – University of Washington researchers have developed a microfluidic-based method for detecting hemoglobin in whole blood.
The technique, which they described in a paper published this week in AIP Advances could enable low-cost point-of-care testing for anemia and prove particularly useful in resource-limited settings, said Nikita Taparia, first author on the study and a graduate student in the lab of University of Washington researcher Nathan Sniadecki.
The method illuminates a whole-blood sample in a microfluidic channel and then uses a CMOS (complementary metal oxide semiconductor) sensor coupled to a lens to detect patient hemoglobin levels. The approach is similar to existing methods for measuring hemoglobin but is simpler in terms of the workflow and equipment required and is capable of assessing levels in whole blood.
This latter point was a central goal of the effort, Taparia said, noting that while hemoglobin testing is typically done on hemolyzed samples, this makes it impossible to perform tests for certain other blood diseases on the same sample.
For instance, she said, labs including Sniadecki's are working on microfluidic devices for detecting platelet disorders. Others are working on devices for detecting conditions like sickle cell disease or malaria. A number of these tests require non-hemolyzed samples, and conventional anemia tests involving lysis of red blood cells are limited in terms of their potential integration with other tests.
In theory, a clinician could take different blood samples for different purposes, but Taparia said that, particularly in resource-constrained areas, additional sample handling leads to additional sources of error, especially when testing is being done by people with limited or no training.
"The thing we are trying to do [in their anemia and other work] is eliminate blood handling altogether," she said.
Optical detection of hemoglobin is based on the fact that the molecule absorbs light at the wavelength of 540nm. This makes it possible to measure its levels in blood by illuminating the sample, and then measuring light absorbance at that wavelength, which will be proportional to the sample's hemoglobin level.
In a conventional lab-based hemoglobin test, a patient sample is lysed to release the hemoglobin from the red blood cells and the hemoglobin is then converted to cyanmethemoglobin, a stabilized form of the analyte. Taparia noted the existence of more streamlined portable hemoglobin tests using, for instance, a smartphone camera to detect light absorption in a cuvette or microfluidic channel, but, she said, these tests also require hemolyzed samples.
Using intact red blood cells presents challenges due to optical scattering, which affects the linearity of hemoglobin measurements.
"Because the cells themselves are intact, light scatters off them," Taparia said. This meant the researchers had to build a calibration curve that took account of the effects of this optical scattering.
She noted, though, that she and her colleagues found this scattering effect to be most pronounced in samples close to the normal hemoglobin range. This means the approach is not able to provide highly accurate hemoglobin measurements for patients with normal levels.
However, Taparia said, this trade-off "is desirable in the sense that we want to focus on people who have anemia."
"We can say, 'Yes, you are normal,' or, 'Yes, you are diseased,' and while we can't say how normal you are, we can definitely say how diseased you are," she said.
In the AIP Advances study, the researchers were able to measure hemoglobin concentrates in patients with severe anemia within 1 g/dL and 3.4 g/dL for moderate anemia, which they noted is sufficient to confidently detect anemia in these populations.
Taparia said that while lab-based tests will also offer higher performance, the hope is that a portable, whole-blood based anemia test integrated with other blood tests could help researchers better assess the levels and causes of anemia in developing world populations, where anemia is most prevalent but still poorly understood.
"If you go into the global health [literature], a lot of it talks about how there is not enough data and detail about … the reason for anemia, especially in places of high anemia risk," she said. "We know, for instance, that this is the level of anemia [in a population] in terms of hemoglobin concentration, but we don't know what kind of anemia it is — whether it is, for instance, from malaria [or], sickle cell."
Taparia said she envisioned an integrated microfluidic device that ran the anemia test as a first-line diagnostic to determine whether or not a patient was anemic, and then passed the sample through additional microfluidic testing chambers to test for different conditions that might be causing the anemia.
"That would add a layer of specificity [to anemia testing] that hasn't existed previously," she said. "Normally, you would need lots of separate tests and a lot more equipment to do that sort of testing. Here, all you would have to do is run one test and it would give you a lot more information."
"For instance, maybe in one region of the world people get a specific type of anemia and in another place in the world they have a totally different state of anemia," she added. "And with that kind of information, down the road you can [explore] how to help treat those specific symptoms. The more specific the information you have, the more specific treatment you can give."
Ultimately, Taparia said, she and her colleagues hope to incorporate the test into microfluidic devices they are developing. In the meantime, though, the hope is that other groups will use their study to integrate similar systems in their own devices.
The device can be built using a basic webcam and LED light, she said. "It's as simple as that."