**3. Point-of-care tests for celiac disease**

### **3.1 Current commercial point-of-care tests**

One of the most widely used commercial kits for celiac disease detection is the new generation of Biocard™ celiac test (AniBiotech®, Vantaa, Finland). In this commercial kit, lateral flow method was utilized to detect human anti-tTG IgA antibodies from a whole blood. Gold-labeled anti-human IgA antibodies are prefixed on the conjugate pad, protein that binds to tTG antigen on the test line and anti-mouse IgG antibody on the control line [19].

The procedure is as follows: first, a drop of whole blood is taken from a finger prick, and then, the assumption is if the blood sample contains anti-tTG antibody, it will complex with liberated self-tTG found on hemolyzed red blood cells. Then the complex will flow to the conjugated pad due to the capillary force, forming a larger complex with anti-human IgA labeled on gold colloids. The larger aggregate is then recognized and captured by the tTG binding protein on the test line, and the red color will appear. The excess gold-labeled anti-IgA antibodies migrate further to control line, combining with anti-mouse IgG antibodies, which is prefixed on the control line, producing another red line (**Figure 2**). Both red lines represent positive result; only one red line in the control line means negative. If neither of the lines turns red, it means the subject is IgA deficient, or the test did not function properly. Usually the result can be viewed within 5–10 min; positive result can even appear after 2 min.

Since the Biocard™ celiac test has been made available on the market, a considerable number of papers have evaluated its sensitivity and specificity. Though the reported sensitivity and specificity vary in a wide range, most of them are around 90%, where some can reach as high as 93 and 94% for sensitivity and specificity, respectively [19–24]. However, this result is slightly lower than laboratory-based celiac disease test (more than 95%); therefore, this commercial kit can be only used for screening for celiac disease, but not for diagnosis. Nevertheless, this test can be also used to detect patients who have IgA antibody deficiency.

Another widely available POCT is Simtomax® Blood Drop system (Augurix SA, Switzerland). It is also a lateral flow assay device but slightly more sophisticated as it presents with two test line, A and B, in addition to a control line [25]. Test line A is used to detect both anti-DGP IgA and IgG antibodies, while test line B is for the detection of the whole IgA antibodies. Control line detects the presence of antibodies by capturing with anti-mouse antibodies. On the test line A, synthetic DGP is embedded to capture and detect anti-DGP IgA and IgG. For the test line B, mouse anti-human IgA detects total IgA. For the conjugate pad, it is secondary antibodies combined with gold colloid. If anti-DGP present in the patient's serum, anti-DGP will be captured by the secondary antibodies in the conjugate pad, and then the

**27**

**Table 1.**

[30].

*Challenges with Point-Of-Care Tests (POCT) for Celiac Disease*

complex will flow further to the test line A and B, captured by A and B, and line A and B will become red. For the control line, goat anti-mouse antibodies are preattached; the excess conjugate of gold colloid with secondary antibodies can interact with it forming red line. All these three lines can be formed after 10 minutes, but not later than 15 min. Three red lines mean that the patient is celiac disease positive and has no IgA deficiency. If only two lines become red, in test line A and control line, then it represents that the subject is positive for celiac disease and IgA deficient, while two red lines, line B and control line, indicate that the subject is healthy, negative for celiac disease, and has IgA deficiency. Only one red line on the control means that the subject is negative for celiac disease but positive for IgA deficiency. If all of these three lines do not turn red demonstrating a non-valid result, meaning the

Various assessments have been done for this commercial kit, and it has been proved to have high sensitivity (95–100%) and specificity (93.1–95.7%) [26–28]. However, specificity of this test drastically reduced when used for patients on a gluten-free diet [26, 29]. This is not surprising as the amount of celiac-related antibodies will decrease with a strict following of gluten-free diet but still can be

Except the above two simple and popular POCT kits, additional lateral flow test has made commercially available, Stick CD 1 and 2 [30]. Stick CD 1 can detect IgA, IgG, and IgM antibodies against human tTG, while Stick CD 2 also detects AGA antibodies. It was demonstrated that the sensitivity of Stick CD 1 was 97% and as to CD 2, 95% for anti-tTG antibodies and 63% for AGA antibodies. The specificity of CD1 has been shown to reach 99%; as for CD 2, it was 99% for anti-tTG antibodies

There are multiple ELISA-based tests that are widely available to identify celiac disease, such as Celikey® or QUANTA®. Typically, these kits use ELISA assay to detect IgA anti-tTG and/or anti-DPG antibodies. The reported sensitivity and specificity have been reported to be higher than 90% [31–33]. QUANTA® products have a various series of commercial kits and can detect different biomarkers with high sensitivity and specificity for celiac disease detection [34] (**Table 1**), including IgA anti-DGP, IgG anti-DGP, IgA human anti-tTG, IgA, and anti-tTG/DGP screening. It can be seen from **Table 1** that the performance of traditional ELISAbased test is still slightly higher than that of any lateral flow tests. This is one of the reasons that most of the gastroenterologists have not accepted the use of POCT as

**Test Sensitivity (95% CI) (%) Specificity (95% CI) (%)** IgA DGP 98.4 (91.4–99.7) 92.7 (85.5–97.1) IgG DGP 95.2 (86.7–99.0) 100.0 (96.2–100.0) IgA human tTG 95.2 (86.7–99.0) 97.9 (92.8–99.7) IgA and IgG DGP screen 96.8 (89.0–99.5) 99.0 (94.4–99.8) tTG/DGP screen 100.0 (94.3–100.0) 92.8 (85.8–97.1)

Although there are some commercial products for the assay of celiac disease in the market, the effort has not been stopped to devise a low-cost kit with high

*Performance of QUANTA lite celiac disease tests in a high-risk population.*

*DOI: http://dx.doi.org/10.5772/intechopen.81874*

patient needs a further test with a new device.

present due to unaware consumption of gluten.

an alternative to the lab-based tests.

**3.2 Research development for point-of-care tests**

**Figure 2.** *Scheme of Biocard™ celiac test.*

## *Challenges with Point-Of-Care Tests (POCT) for Celiac Disease DOI: http://dx.doi.org/10.5772/intechopen.81874*

*Celiac Disease - From the Bench to the Clinic*

anti-mouse IgG antibody on the control line [19].

this commercial kit, lateral flow method was utilized to detect human anti-tTG IgA antibodies from a whole blood. Gold-labeled anti-human IgA antibodies are prefixed on the conjugate pad, protein that binds to tTG antigen on the test line and

The procedure is as follows: first, a drop of whole blood is taken from a finger prick, and then, the assumption is if the blood sample contains anti-tTG antibody, it will complex with liberated self-tTG found on hemolyzed red blood cells. Then the complex will flow to the conjugated pad due to the capillary force, forming a larger complex with anti-human IgA labeled on gold colloids. The larger aggregate is then recognized and captured by the tTG binding protein on the test line, and the red color will appear. The excess gold-labeled anti-IgA antibodies migrate further to control line, combining with anti-mouse IgG antibodies, which is prefixed on the control line, producing another red line (**Figure 2**). Both red lines represent positive result; only one red line in the control line means negative. If neither of the lines turns red, it means the subject is IgA deficient, or the test did not function properly. Usually the result can be viewed within 5–10 min; positive result can even appear

Since the Biocard™ celiac test has been made available on the market, a considerable number of papers have evaluated its sensitivity and specificity. Though the reported sensitivity and specificity vary in a wide range, most of them are around 90%, where some can reach as high as 93 and 94% for sensitivity and specificity, respectively [19–24]. However, this result is slightly lower than laboratory-based celiac disease test (more than 95%); therefore, this commercial kit can be only used for screening for celiac disease, but not for diagnosis. Nevertheless, this test can be

Another widely available POCT is Simtomax® Blood Drop system (Augurix SA, Switzerland). It is also a lateral flow assay device but slightly more sophisticated as it presents with two test line, A and B, in addition to a control line [25]. Test line A is used to detect both anti-DGP IgA and IgG antibodies, while test line B is for the detection of the whole IgA antibodies. Control line detects the presence of antibodies by capturing with anti-mouse antibodies. On the test line A, synthetic DGP is embedded to capture and detect anti-DGP IgA and IgG. For the test line B, mouse anti-human IgA detects total IgA. For the conjugate pad, it is secondary antibodies combined with gold colloid. If anti-DGP present in the patient's serum, anti-DGP will be captured by the secondary antibodies in the conjugate pad, and then the

also used to detect patients who have IgA antibody deficiency.

**26**

**Figure 2.**

after 2 min.

*Scheme of Biocard™ celiac test.*

complex will flow further to the test line A and B, captured by A and B, and line A and B will become red. For the control line, goat anti-mouse antibodies are preattached; the excess conjugate of gold colloid with secondary antibodies can interact with it forming red line. All these three lines can be formed after 10 minutes, but not later than 15 min. Three red lines mean that the patient is celiac disease positive and has no IgA deficiency. If only two lines become red, in test line A and control line, then it represents that the subject is positive for celiac disease and IgA deficient, while two red lines, line B and control line, indicate that the subject is healthy, negative for celiac disease, and has IgA deficiency. Only one red line on the control means that the subject is negative for celiac disease but positive for IgA deficiency. If all of these three lines do not turn red demonstrating a non-valid result, meaning the patient needs a further test with a new device.

Various assessments have been done for this commercial kit, and it has been proved to have high sensitivity (95–100%) and specificity (93.1–95.7%) [26–28]. However, specificity of this test drastically reduced when used for patients on a gluten-free diet [26, 29]. This is not surprising as the amount of celiac-related antibodies will decrease with a strict following of gluten-free diet but still can be present due to unaware consumption of gluten.

Except the above two simple and popular POCT kits, additional lateral flow test has made commercially available, Stick CD 1 and 2 [30]. Stick CD 1 can detect IgA, IgG, and IgM antibodies against human tTG, while Stick CD 2 also detects AGA antibodies. It was demonstrated that the sensitivity of Stick CD 1 was 97% and as to CD 2, 95% for anti-tTG antibodies and 63% for AGA antibodies. The specificity of CD1 has been shown to reach 99%; as for CD 2, it was 99% for anti-tTG antibodies [30].

There are multiple ELISA-based tests that are widely available to identify celiac disease, such as Celikey® or QUANTA®. Typically, these kits use ELISA assay to detect IgA anti-tTG and/or anti-DPG antibodies. The reported sensitivity and specificity have been reported to be higher than 90% [31–33]. QUANTA® products have a various series of commercial kits and can detect different biomarkers with high sensitivity and specificity for celiac disease detection [34] (**Table 1**), including IgA anti-DGP, IgG anti-DGP, IgA human anti-tTG, IgA, and anti-tTG/DGP screening. It can be seen from **Table 1** that the performance of traditional ELISAbased test is still slightly higher than that of any lateral flow tests. This is one of the reasons that most of the gastroenterologists have not accepted the use of POCT as an alternative to the lab-based tests.
