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Finger-prick blood tests can deliver inaccurate results, according to a study published in the American Journal of Clinical Pathology.
Investigators found that results varied greatly when they performed multiple finger-prick tests on a single subject.
However, averaging the results of multiple droplet tests allowed the investigators to achieve results on par with venous blood tests.
They required 6 to 9 drops of blood to achieve consistent results.
“We began looking at this after we got some surprising results from our controls in an earlier study,” explained lead investigator Rebecca Richards-Kortum, PhD, of Rice University in Houston, Texas.
“Students in my lab are developing novel, low-cost platforms for anemia, platelet, and white blood cell testing in low-resource settings, and one of my students, Meaghan Bond, noticed there was wide variation in some of the benchmark tests that she was performing on hospital-grade blood analyzers.”
The benchmark controls are used to gauge the accuracy of test results from the new technology under study, so the variation among the control data was a sign that something was amiss.
What wasn’t immediately clear was whether the readings resulted from a problem with the current experiments or actual variations in the amount of hemoglobin, platelets, and white blood cells in the different drops of blood.
So Dr Richards-Kortum and Bond designed a simple protocol to test whether there was actual variation and, if so, how much.
They drew 6 successive 20 µL droplets of blood from 11 donors. As an additional test to determine whether minimum droplet size might also affect the results, the pair drew 10 successive 10 µL droplets from 7 additional donors.
All droplets were drawn from the same finger prick, and the investigators followed best practices in obtaining the droplets. The first drop was wiped away to remove contamination from disinfectants, and the finger was not squeezed or “milked,” which can lead to inaccurate results.
For experimental controls, the investigators used venipuncture to draw tubes of blood from an arm vein.
Each 20 µL droplet was analyzed with a hospital-grade blood analyzer for hemoglobin concentration, total white blood cell count, platelet count, and 3-part white blood cell differential. Each 10 µL droplet was tested for hemoglobin concentration with a popular point-of-care blood analyzer.
“A growing number of clinically important tests are performed using finger-prick blood, and this is especially true in low-resource settings,” Bond noted.
“It is important to understand how variations in finger-prick blood collection protocols can affect point-of-care test accuracy as well as how results might vary between different kinds of point-of-care tests that use finger-prick blood from the same patient.”
She and Dr Richards-Kortum found that hemoglobin content, platelet count, and white blood cell count each varied significantly from blood drop to blood drop.
“Some of the differences were surprising,” Bond said. “For example, in some donors, the hemoglobin concentration changed by more than 2 g/dL in the span of 2 successive drops of blood.”
Fortunately, the investigators found that averaging the results of the droplet tests could produce results that were on par with venous blood tests, but tests on 6 to 9 drops of blood were needed to achieve consistent results.
“Finger-prick blood tests can be accurate, and they are an important tool for healthcare providers, particularly in point-of-care and low-resource settings,” Bond said.
“Our results show that people need to take care to administer finger-prick tests in a way that produces accurate results because accuracy in these tests is increasingly important for diagnosing conditions like anemia, infections, and sickle cell anemia, malaria, HIV, and other diseases.” 
Finger-prick blood tests can deliver inaccurate results, according to a study published in the American Journal of Clinical Pathology.
Investigators found that results varied greatly when they performed multiple finger-prick tests on a single subject.
However, averaging the results of multiple droplet tests allowed the investigators to achieve results on par with venous blood tests.
They required 6 to 9 drops of blood to achieve consistent results.
“We began looking at this after we got some surprising results from our controls in an earlier study,” explained lead investigator Rebecca Richards-Kortum, PhD, of Rice University in Houston, Texas.
“Students in my lab are developing novel, low-cost platforms for anemia, platelet, and white blood cell testing in low-resource settings, and one of my students, Meaghan Bond, noticed there was wide variation in some of the benchmark tests that she was performing on hospital-grade blood analyzers.”
The benchmark controls are used to gauge the accuracy of test results from the new technology under study, so the variation among the control data was a sign that something was amiss.
What wasn’t immediately clear was whether the readings resulted from a problem with the current experiments or actual variations in the amount of hemoglobin, platelets, and white blood cells in the different drops of blood.
So Dr Richards-Kortum and Bond designed a simple protocol to test whether there was actual variation and, if so, how much.
They drew 6 successive 20 µL droplets of blood from 11 donors. As an additional test to determine whether minimum droplet size might also affect the results, the pair drew 10 successive 10 µL droplets from 7 additional donors.
All droplets were drawn from the same finger prick, and the investigators followed best practices in obtaining the droplets. The first drop was wiped away to remove contamination from disinfectants, and the finger was not squeezed or “milked,” which can lead to inaccurate results.
For experimental controls, the investigators used venipuncture to draw tubes of blood from an arm vein.
Each 20 µL droplet was analyzed with a hospital-grade blood analyzer for hemoglobin concentration, total white blood cell count, platelet count, and 3-part white blood cell differential. Each 10 µL droplet was tested for hemoglobin concentration with a popular point-of-care blood analyzer.
“A growing number of clinically important tests are performed using finger-prick blood, and this is especially true in low-resource settings,” Bond noted.
“It is important to understand how variations in finger-prick blood collection protocols can affect point-of-care test accuracy as well as how results might vary between different kinds of point-of-care tests that use finger-prick blood from the same patient.”
She and Dr Richards-Kortum found that hemoglobin content, platelet count, and white blood cell count each varied significantly from blood drop to blood drop.
“Some of the differences were surprising,” Bond said. “For example, in some donors, the hemoglobin concentration changed by more than 2 g/dL in the span of 2 successive drops of blood.”
Fortunately, the investigators found that averaging the results of the droplet tests could produce results that were on par with venous blood tests, but tests on 6 to 9 drops of blood were needed to achieve consistent results.
“Finger-prick blood tests can be accurate, and they are an important tool for healthcare providers, particularly in point-of-care and low-resource settings,” Bond said.
“Our results show that people need to take care to administer finger-prick tests in a way that produces accurate results because accuracy in these tests is increasingly important for diagnosing conditions like anemia, infections, and sickle cell anemia, malaria, HIV, and other diseases.”
Finger-prick blood tests can deliver inaccurate results, according to a study published in the American Journal of Clinical Pathology.
Investigators found that results varied greatly when they performed multiple finger-prick tests on a single subject.
However, averaging the results of multiple droplet tests allowed the investigators to achieve results on par with venous blood tests.
They required 6 to 9 drops of blood to achieve consistent results.
“We began looking at this after we got some surprising results from our controls in an earlier study,” explained lead investigator Rebecca Richards-Kortum, PhD, of Rice University in Houston, Texas.
“Students in my lab are developing novel, low-cost platforms for anemia, platelet, and white blood cell testing in low-resource settings, and one of my students, Meaghan Bond, noticed there was wide variation in some of the benchmark tests that she was performing on hospital-grade blood analyzers.”
The benchmark controls are used to gauge the accuracy of test results from the new technology under study, so the variation among the control data was a sign that something was amiss.
What wasn’t immediately clear was whether the readings resulted from a problem with the current experiments or actual variations in the amount of hemoglobin, platelets, and white blood cells in the different drops of blood.
So Dr Richards-Kortum and Bond designed a simple protocol to test whether there was actual variation and, if so, how much.
They drew 6 successive 20 µL droplets of blood from 11 donors. As an additional test to determine whether minimum droplet size might also affect the results, the pair drew 10 successive 10 µL droplets from 7 additional donors.
All droplets were drawn from the same finger prick, and the investigators followed best practices in obtaining the droplets. The first drop was wiped away to remove contamination from disinfectants, and the finger was not squeezed or “milked,” which can lead to inaccurate results.
For experimental controls, the investigators used venipuncture to draw tubes of blood from an arm vein.
Each 20 µL droplet was analyzed with a hospital-grade blood analyzer for hemoglobin concentration, total white blood cell count, platelet count, and 3-part white blood cell differential. Each 10 µL droplet was tested for hemoglobin concentration with a popular point-of-care blood analyzer.
“A growing number of clinically important tests are performed using finger-prick blood, and this is especially true in low-resource settings,” Bond noted.
“It is important to understand how variations in finger-prick blood collection protocols can affect point-of-care test accuracy as well as how results might vary between different kinds of point-of-care tests that use finger-prick blood from the same patient.”
She and Dr Richards-Kortum found that hemoglobin content, platelet count, and white blood cell count each varied significantly from blood drop to blood drop.
“Some of the differences were surprising,” Bond said. “For example, in some donors, the hemoglobin concentration changed by more than 2 g/dL in the span of 2 successive drops of blood.”
Fortunately, the investigators found that averaging the results of the droplet tests could produce results that were on par with venous blood tests, but tests on 6 to 9 drops of blood were needed to achieve consistent results.
“Finger-prick blood tests can be accurate, and they are an important tool for healthcare providers, particularly in point-of-care and low-resource settings,” Bond said.
“Our results show that people need to take care to administer finger-prick tests in a way that produces accurate results because accuracy in these tests is increasingly important for diagnosing conditions like anemia, infections, and sickle cell anemia, malaria, HIV, and other diseases.”