Validation of IgG Levels Test Using Capillary Blood

Introduction

In some individuals, the consumption of certain foods can trigger symptoms such as rashes, joint pain, brain fog, abdominal pain and fatigue that are not due to food allergies (IgE-mediated reactions) or food intolerances (reactions due to enzyme deficiency) [1] . Symptoms can occur hours to days after eating the trigger food and people may not notice they have one due to delayed and indistinct reaction. These are often referred to as food sensitivities. Food sensitivities are typically identified through a trial-and-error approach where certain foods are temporarily removed and subsequently reintroduced into the diet to identify potential triggers [2] . This is often a long and tedious process carried out under the supervision of a healthcare practitioner. Though the exact cause of food sensitivities remains unclear, the symptoms are believed to be caused by immune reactions (increased levels in IgG antibodies) to certain foods [1] . As such, the measurement of food-specific antibodies (IgG) has been proposed to help identify foods that trigger symptoms in affected individuals [3] . IgG are the most abundant antibodies circulating in the body and they are present in both healthy and symptomatic individuals as part of the normal immune response to food [4] . Studies have found that eliminating food with high IgG reactivity helps to reduce symptoms in various conditions such as Irritable Bowel Syndrome (IBS) [5-12] , migraine [10-16] and Crohn’s Disease [17-19] .

In the clinical setting, IgG testing is typically used to screen for immune-mediated disorders such as coeliac disease [20] as well as for prior infections or vaccinations such as in the case of COVID-19 [21] . Many antibody tests use serum or plasma from blood samples collected by venipuncture. However, venipuncture is an invasive and uncomfortable procedure that is often hampered by logistical challenges associated with collecting, processing, and transporting venous blood [22] .

In this study, we compared the IgG levels from capillary blood sampling versus the IgG levels in blood samples taken via venipuncture. We also evaluated the stability of the samples collected at days 1, 2, 3 and 4 following sample collection and also tested the stability of samples under varying temperature conditions.

Methods & Results

A total of 31 individuals who provided informed consent were included in this study. Two samples were collected from each individual – a venous blood sample and a capillary blood sample on the same day around the same time. The venous blood samples and the capillary blood samples were measured at different time points and at different temperatures as shown in Tables 1 and 2.

Briefly, the IgG assay for 96 food types was performed on both these samples using the EuroBlotOne system. The IgG levels in capillary blood were compared to the IgG levels in venous blood and the correlation coefficients are listed in Table 3. The IgG levels were further stratified into 4 different classes to represent different reactivity to different foods. As such, the difference between the classes were also assessed. The difference in IgG levels in classes 0 and 1 versus the IgG levels in classes 2 and 3 reached statistical significance and correlated well with those measured from venous blood (Table 4).

Table 1. Table showing the time points and temperatures at which the tests were performed. Room temp is 22°C.

Number of Samples	Time point of measurement	Temperature setting
5	1 day	Room temp
1	2 days	Room temp
6	3 days	Room temp
2	4 days	Room temp
5	5 days	Temperature cycle 1
12	7 days	Temperature cycle 2

Table 2. Temperature cycling of samples beginning from when they were collected.

Temperature	Hours
22°C	1h
32°C	7h
22°C	14h
27°C	2h
22°C	23h

Table 3:  The correlation coefficients of IgG levels measured at different time points and temperature cycling conditions

Time point of measurement	Correlation Coefficient
24 hours	0.98
48 hours	0.98
72 hours	0.97
96 hours	0.99
Temperature Cycle 1	0.98
Temperature Cycle 2	0.99

Table 4:  The match rate of classes measured at different time points and temperature cycling conditions

Time point of measurement	Correlation Coefficient
24 hours	0.99
48 hours	1
72 hours	0.99
96 hours	1
Temperature Cycle 1	0.99
Temperature Cycle 2	0.99

Conclusion

The present study shows that the IgG levels measured using capillary blood were comparable with those measured using venous blood, with a correlation coefficient of 0.98 at 24 hours after collection. This study also shows that the IgG levels in capillary blood are stable for up to 4 days and at high temperature.

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