What Can a Drop of Blood Tell You?

Blood is a treasure trove of information that provides clues to an individual’s internal metabolic status. However, obtaining the blood can be a challenge. In this blog post, the ODX Research team dives deep into the topic of blood spot testing, comparing it with the more traditional venous blood testing.

Substantial amounts of blood can be obtained from a venous blood draw, but some individuals may be averse to having their blood drawn or may only have blood drawn once per year. An alternative, less invasive method of obtaining blood samples is a capillary or “fingerstick” blood draw, which uses just a small amount of blood applied to standardized filter paper. The dried blood spot (DBS) method of obtaining and processing capillary blood samples is used for evaluating nutritional and infectious disease status, as well as immune, endocrine, reproductive, and metabolic function. The DBS method has been used widely in NIH-funded research, including National Health and Nutrition Examination Surveys (NHANES), the National Health and Retirement Study, and the National Longitudinal Study of Adolescent Health (Barr 2021).

Capillary Blood Testing Overview

Taking a small “micro” blood sample is less invasive and more convenient than a venous blood draw. Microsampling techniques include dried blood spot (DBS), volumetric absorptive microsampling (VAMS), and use of specialty devices such as Tasso, TAP, and Mitra. The most common microsampling technique is the dried blood spot method which uses 50-75 uL of blood to yield 4-6 spots that must be dried for four hours prior to testing. While DBS can be cost-effective, it also has limitations that must be considered (AACC 2022):

• Hematocrit effect (especially if “milking” the puncture site which increases the content of interstitial fluid in the sample)
• Improper sample collection
• Age and medical conditions can impact hematocrit, sample viscosity, and application of the blood to the filter paper
• High humidity and temperature can negatively affect the sample
• Sample heterogeneity
• Low sample volume
• Long drying time
• Labor-intensive processing 

Non-exhaustive list of pre-analytical considerations when using dried blood spot (DBS) in field settings.

Source: Lim, Mark D. “Dried Blood Spots for Global Health Diagnostics and Surveillance: Opportunities and Challenges.” The American journal of tropical medicine and hygiene vol. 99,2 (2018): 256-265. doi:10.4269/ajtmh.17-0889 https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/29968557/  This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

The use of capillary dried blood spot testing has been utilized and improved over the past century and is currently applied in epidemiological and infectious disease research, environmental monitoring, drug monitoring, and newborn and metabolic screening.

As of 2001, DBS testing is used to evaluate more than 175 biomarkers, including glucose, lipoproteins, acylcarnitines, C-reactive protein, vitamin A, selenium, zinc, other trace elements, prolactin, cytokines, protoporphyrin, various medications, hepatitis B, and antibodies to over 30 viruses.

Blood spot testing is accepted and considered valid in the field of laboratory testing, and many biomarker results are comparable to venous blood testing. However, not all DBS ranges parallel venous blood biomarker ranges, and specific diagnostic decision levels may need to be considered when utilizing blood spot testing (Li 2014). 

Capillary blood testing is used to assess exposure to specific environmental toxins in adults and children. The DBS method can be used to detect persistent organic pollutants (POPs), including PCBs, organochlorine pesticides, and flame retardants, as well as other toxins such as bisphenol A, phthalates, and various pesticides. The use of DBS avoids the potential phthalate contamination of the sample that can occur with a venous blood draw (Barr 2021).

Capillary blood results tend to correlate better with circulating levels than urine or saliva results do. However, clinical reference ranges and cut-offs are often adjusted for DBS testing to account for subtle differences between capillary and venous values. Dried blood spot testing may be especially useful in evaluating micronutrient status in a large-scale or community-based application. For example, DBS testing of thyroid function was used to monitor response to iodine supplementation in a study of 377 Moroccan children with limited access to healthcare. Dried blood spot testing was also utilized in the HIM study evaluation of men’s health and behaviors. The DBS method was employed in the Demographic and Health Surveys (DHSs) designed to incorporate widespread biomarker testing in the general population. The DHS program has evaluated more than 16 biomarkers in 80 countries comprising millions of participants (Brindle 2014).  

The quality of the DBS sample determines its accuracy. Appropriate training can reduce potential adverse environmental effects associated with collecting dried blood spots. Obtaining an adequate amount of blood appears to be one of the most significant variables in DBS testing. Considering the need to account for varying spot sizes, temperature exposure, and drying times, correction formulae that provide a high degree of accuracy in comparing capillary DBS results to venous blood draw results have been proposed (Borsch-Supan 2021).

Capillary Blood Testing Applications

Dried blood spot samples were collected from 27,000 participants in The Survey of Health, Ageing and Retirement in Europe (SHARE) study. The DBS method was used to evaluate several biomarkers associated with chronic disease, including:

• ApoE
• Brain-derived neurotrophic factor (BDNF)
• Cholesterol, total
• Clusterin
• C-reactive protein 
• Cystatin C
• HDL
• Hemoglobin A1C
• Hemoglobin, total
• Inflammatory cytokines e.g., IL-8, IL-16, IL-18
• Triglycerides
• Vascular epithelial growth factor (VEGF)
• Vitamin D

Researchers note that many results obtained via DBS cannot automatically be compared to reference ranges based on venous blood draw results and that some biomarkers are more sensitive to processing factors such as small spot size, short drying time, and long shipment times. Measuring total cholesterol via DBS appears to be particularly challenging and can correlate poorly with venous blood samples. However, researchers suggest that correction formulae can be developed to compare results obtained from DBS to venous blood samples and reference ranges (Borsch-Supan 2019).

Comparison of laboratory results of DBS and plasma

Source: Borsch-Supan, Axel, Martina Börsch-Supan, and Luzia M. Weiss. "36 Dried blood spot samples and their validation." Health and socio–economic status over the life c 349. 2019. https://library.oapen.org/bitstream/handle/20.500.12657/23548/1006598.pdf?sequence#page=367
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. https://doi.org/10.1515/9783110617245-002

Utilizing the data of 150 individuals from The Be Well Work Well study and the Sleep and Cardiovascular Disease Risk study, researchers determined DBS to serum equivalencies providing R2 values for total cholesterol, HDL-C, and CRP of 0.484, 0.118, 0.666, respectively (Samuelsson 2015).

Another study compared DBS to serum cholesterol in 317 blood samples, with serum cholesterol levels ranging from 81-337 mg/dL (2.1-8.83 mmol/L). The DBS method was found to overestimate total cholesterol when levels were low in the blood and underestimate it when blood levels were high. Researchers note that the DBS method may reflect cholesterol found in erythrocyte membranes better than serum or plasma samples and that this may factor into the discrepancy between DBS and circulating cholesterol. Ultimately, researchers conclude that use of a correlation coefficient (r) of 0.611 allowed them to predict serum cholesterol from the DBS sample without a significant difference between the two results (Corso 2016).

Blood spot testing was used effectively and found comparable to venipuncture in assessing liver function tests, including ALT, AST, total bilirubin, creatinine, alkaline phosphatase, albumin, magnesium, and phosphorus (Wickremsinhe 2022).   

Screening for diabetes and prediabetes can be done using capillary blood testing to test fasting glucose levels. In a study of 993 randomly selected subjects, 57 individuals were diagnosed with diabetes (previously undetected), and 145 individuals were diagnosed with pre-diabetes using capillary blood sampling and results were confirmed with oral glucose tolerance testing, highlighting the value of this method for diabetes screening in a rural population (Zhao 2013).

Dried blood spot glucose testing in 307 pregnant women revealed DBS glucose levels ranging from 53-166 mg/dL (2.94-9.21 mmol/L) versus plasma results of 66-190 mg/dL (3.66-10.55 mmol/L). Researchers note that DBS glucose results had good correlation with plasma glucose but not good concordance, highlighting the difference between the two metrics. However, researchers found the data obtained from DBS testing valuable and applicable in the clinical setting (Matos 2020).

Screening for autoantibodies associated with type 1 diabetes can be accomplished using DBS technology as well. In a study of 229 relatives of type 1 diabetics, DBS testing accurately identified 95.5% of individuals positive for antibodies with venous blood testing, and 98.6% of those negative for antibodies with venous testing (Bingley 2015).

The DBS method is also used to evaluate the Omega-3 Index, a measurement of the EPA and DHA content of red blood cells. Samples were found to be viable for at least six weeks at room temperature, three years at -20 degrees Celsius, and four years at -80 degrees Celsius when using antioxidant-treated filter paper (Harris 2016).

One study comparing capillary 25(OH)D levels to venous levels found that capillary blood results were significantly higher at 43.27 ng/mL (108 nmol/L) versus 36.6 ng/mL (90 nmol/L) in venous blood samples (Dayre 2008).

Dried blood spot testing has been used for hs-CRP, a biomarker of acute and chronic inflammation, infection, morbidity, and mortality. One study comparing various testing methods found that DBS samples from capillary and venous blood were comparable but were approximately 31-33% lower than serum results. Plasma results were approximately 7% lower than serum results in this study. Researchers note that DBS CRP samples can degrade in long-term storage of more than 20 days at ambient temperature or more than one year at -20 degrees Celsius, though they did not attribute differences DBS versus serum results to degradation in this study (Brindle 2010). Degradation of DBS samples in IgE testing has also been observed, and researchers recommend refrigerating or freezing samples within one to two days of collection (Tanner 2007).

A cross-sectional study of reproductive-age women 18-35 found that blood spot levels of estradiol, FSH, LH, and progesterone correlated well with plasma levels. Researchers concluded that blood spot testing was superior for documenting hormonal changes over time and picked up LH peaks missed by biweekly venipuncture results (Edelman 2007).

Capillary dried blood spot testing for evaluation of progesterone levels may more accurately reflect tissue levels and help guide therapeutic dosing than venous blood samples. One study of 10 postmenopausal women found that capillary blood levels of progesterone were 100 times higher than serum levels, suggesting that dosing based on the lower venous values may lead to an overdose of progesterone (Du 2013).

Optimal Takeaways

• Capillary blood testing offers a viable alternative to a venous blood draw in the evaluation of several biomarkers.
• Reference ranges for venous blood samples cannot automatically be applied to capillary blood results and ranges may need to be adjusted depending on the biomarker.
• The process of obtaining and processing capillary blood samples significantly affects the quality of the sample and the validity of test results. 

References

American Association for Clinical Chemistry (AACC). Dried Blood Spots and Beyond. September 1, 2022. 

Barr, Dana Boyd et al. “The use of dried blood spots for characterizing children's exposure to organic environmental chemicals.” Environmental research vol. 195 (2021): 110796. doi:10.1016/j.envres.2021.110796 

Bingley, Polly J et al. “Use of Dried Capillary Blood Sampling for Islet Autoantibody Screening in Relatives: A Feasibility Study.” Diabetes technology & therapeutics vol. 17,12 (2015): 867-71. doi:10.1089/dia.2015.0133 

Borsch-Supan, Axel et al. “Dried blood spot collection, sample quality, and fieldwork conditions: Structural validations for conversion into standard values.” American journal of human biology : the official journal of the Human Biology Council vol. 33,4 (2021): e23517. doi:10.1002/ajhb.23517 

Brindle, Eleanor et al. “Serum, plasma, and dried blood spot high-sensitivity C-reactive protein enzyme immunoassay for population research.” Journal of immunological methods vol. 362,1-2 (2010): 112-20. doi:10.1016/j.jim.2010.09.014 

Brindle, Eleanor, Kathleen A. O'Connor, and Dean A. Garrett. "Applications of dried blood spots in general human health studies." Dried blood spots: Applications and techniques (2014): 114-129.

Corso, Gaetano et al. “Development and Validation of an Enzymatic Method for Total Cholesterol Analysis Using Whole Blood Spot.” Journal of clinical laboratory analysis vol. 30,5 (2016): 517-23. doi:10.1002/jcla.21890 

Dayre McNally, J et al. “Capillary blood sampling as an alternative to venipuncture in the assessment of serum 25 hydroxyvitamin D levels.” The Journal of steroid biochemistry and molecular biology vol. 112,1-3 (2008): 164-8. doi:10.1016/j.jsbmb.2008.08.006

Du, Joanna Y et al. “Percutaneous progesterone delivery via cream or gel application in postmenopausal women: a randomized cross-over study of progesterone levels in serum, whole blood, saliva, and capillary blood.” Menopause (New York, N.Y.) vol. 20,11 (2013): 1169-75. doi:10.1097/GME.0b013e31828d39a2 

Edelman, Alison et al. “A comparison of blood spot vs. plasma analysis of gonadotropin and ovarian steroid hormone levels in reproductive-age women.” Fertility and sterility vol. 88,5 (2007): 1404-7. doi:10.1016/j.fertnstert.2006.12.016 

Harris, William S., and Jason Polreis. "Measurement of the omega-3 index in dried blood spots." Ann Clin Lab Res 4.4 (2016): 137. 

Li, Wenkui, et al. "Dried blood spots." Applications and Techniques (2014): VIII-IX.

Matos, Ana Lígia Soares et al. “Comparison of glucose measurement on dried blood spots versus plasma samples in pregnant women with and without anemia.” Archives of endocrinology and metabolism vol. 64,4 (2020): 454-461. doi:10.20945/2359-3997000000229 

Samuelsson, Laura B et al. “Validation of Biomarkers of CVD Risk from Dried Blood Spots in Community-Based Research: Methodologies and Study-Specific Serum Equivalencies.” Biodemography and social biology vol. 61,3 (2015): 285-97. doi:10.1080/19485565.2015.1068105 

Tanner, Susan, and Thomas W McDade. “Enzyme immunoassay for total immunoglobulin E in dried blood spots.” American journal of human biology : the official journal of the Human Biology Council vol. 19,3 (2007): 440-2. doi:10.1002/ajhb.20635 

Wickremsinhe, Enaksha et al. “Standard Venipuncture vs a Capillary Blood Collection Device for the Prospective Determination of Abnormal Liver Chemistry.” The journal of applied laboratory medicine, jfac127. 19 Dec. 2022, 

Zhao, X et al. “Fasting capillary blood glucose: an appropriate measurement in screening for diabetes and pre-diabetes in low-resource rural settings.” Journal of endocrinological investigation vol. 36,1 (2013): 33-7. doi:10.3275/8304