**1. Introduction**

Celiac disease is defined as a lifelong condition as a result of ingestion of gluten among genetically susceptible people that can be relieved by the introduction of gluten-free diet; the condition relapses with gluten intake [1]. Recent studies show that it is prevalent around the world, covering from the western world, such as Europe and America, to Oceania, Africa, and Asia. The number of celiac sufferers increases, doubling its number every two decades [2]. The symptoms vary at a wide range, from flatulence, constipation, anorexia, irregular bowel habits, and irritability to numbness in limbs, foggy mind, diarrhea, and depression [3]. Therefore, it is hard to recognize the condition and deliver the diagnosis. In fact, almost 90% of celiac patients remain undiagnosed, due to the nonspecific or absent symptoms over a long period [4]. Thereby, it is of paramount significance to achieve the early-stage diagnosis of celiac disease that can lead to improving the patients' quality of life.

The current gold standard of celiac disease diagnosis, which has been also developed in a much earlier period, is to observe the small intestine atrophy obtained

through biopsy [1]. This process is highly invasive, time-consuming, and inconvenient to both patients and clinicians.

Over the last several decades, researchers have found that the concentration of some certain antibodies circulating in celiac patients' body increased, and the detection of celiac disease can be achieved with the detection of these antibodies. In fact, the surface of mucosa represents the major targeted sites when foreign antigens attack the body [5]. Plausibly, 80% of all cells producing immunoglobulin (IgG) in the human body are in small bowel mucosa, which also produces the dimers of IgA [6]. Therefore, the antibodies of celiac disease among untreated patients are located in the mucosal surface [7], as extracellular deposit, some present in jejunal juice [8], and most in the intestine [9, 10]. For untreated celiac patients, the additional generation of antibodies leads to an increase of antibodies specific to celiac disease (IgA− class), most of which can be found in the circulating blood and some other bodily fluids. Among all the celiac-specific antibodies, anti-reticulin (ARA), anti-jejunal (JEA), endomysial (EMA), and tissue transglutaminase antibodies (tTG) are among the patients' own endogenous biomolecules that form as a result of immune response to antigen in the intestine, whereas anti-gliadin antibody (AGA) and deamidated gliadin peptide antibody (DGP-Ab) are formed directly against dietary gliadin [11].

Over the years, the detection of the celiac-related antibodies has shown promising results, and whole blood- or serum-based pathology tests are regularly used for screening for celiac disease. Typically, screening for celiac disease includes tests for identification of titers for AGA and/or anti-tTG antibodies, and most of these tests are based on enzyme-linked immunoassays (ELISA). Even though the method of ELISA can reach a high sensitivity and specificity, these tests cannot be used on their own in the process of celiac disease diagnosis. Furthermore, pathology tests are typically confined to centralized laboratories, where expert personnel is required, leading to slow- and high-cost detections. Thereby, it is not suitable for the use outside hospitals, such as clinical offices or home settings, leaving a high number of undiagnosed celiac cases, especially when their symptoms are not obvious or do not affect their normal life. Thus, simple and rapid detection methods are in high demand to be developed.

Fast, accurate, and noninvasive early diagnosis methods and/or devices are needed to achieve the detection of celiac disease with high sensitivity and specificity, especially facing the rapid increasing number of celiac patients. Over the last decade, several point-of-care blood tests have been developed and applied for celiac diseases screening. The most prominent tests are Simtomax® Blood Drop system (Augurix SA, Switzerland) and Biocard™ celiac test (AniBiotech®, Finland), lateral flow immunoassays that detect anti-tTG and/or anti-deamidated gliadin peptide antibodies.

Lateral flow test, also called lateral flow immunoassay or test strip, has been widely and commercially used in the rapid detection of many diseases and conditions, such as HIV, illicit drugs, and early pregnancy [12]. In the following sections, we will discuss and compare several commercial kits available as POCT devices for celiac disease. The principle of lateral flow test is outlined in the next section.

## **2. Lateral flow immunoassays**

Lateral flow immunoassay is a simple immunochromatography technology that has successfully applied for rapid diagnostic testing [12, 13]. It typically made of nitrocellulose or paper-based porous membrane that makes it ideal to fabricate low-cost devices with little maintenance requirements. Porous membrane enables the separation, capture, and recognition of the target analytes. In addition, porous

**25**

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

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

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

*Schematic representation of lateral flow immunoassay in a capture format. Various important parts of the test are identified as sample, conjugate, and absorbent pads, nitrocellulose membrane with test and control lines.*

nature of the material facilitates movement of fluids, such as a whole blood, serum,

There are several types of lateral flow assays available, but the most popular is the capture format. There are two types of capture: "sandwich" and competitive

Overall, lateral flow immunoassay consists of four parts: sample pad, conjugate pad, nitrocellulose membrane (test line and control line labeled on it), and absorbent pad (also called wicking; **Figure 1**). Typically, fluid sample (blood, serum, urine, saliva) is added onto sample pad. Through the capillary action, the liquid moves to the conjugate pad, where preloaded recognition element (conjugated nanoparticles or colored reagent) is imbedded. The sample and the recognition reagent react commonly through antigen-antibody interaction. The sample together with the recognition element continues flowing within nitrocellulose membrane toward test and control lines. Depending on the type of a capture, sandwich or competitive, the test line would show a colorful line or disappear, respectively. Control line always shows colorful signal to indicate the correct functionality of the test. Absorbent pad function is to collect all the unreacted reagents as well as excess

Lateral flow immunoassay for celiac disease is typically used to detect antibodies, such as anti-tTG, anti-DGP, and AGA antibodies from the whole blood or serum in a sandwich type of detection [14–18]. Preloaded reagent can be gold nanoparticles or dye conjugated to antigens, such as transglutaminase, deamidated gliadin peptides, and gliadin protein fragments. The detection of celiac disease-related antibodies will present as color test line that can be usually seen by the naked eye. Lateral flow test or strip test is often used as a point-of-care test (POCT) due to its high specificity, visual color confirmation, and, especially, because of no additional instrumentation is required. In fact, most of the current commercial POCTs for celiac disease are based on lateral flow assay to detect antibodies. In the following section, we will discuss and make a comparison among commercial kits available together with the outlining principles of POCT device for celiac disease.

One of the most widely used commercial kits for celiac disease detection is the new generation of Biocard™ celiac test (AniBiotech®, Vantaa, Finland). In

or urine, by means of capillary action with no external force required.

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

**Figure 1.**

capture [13].

of liquids.

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

**Figure 1.**

*Celiac Disease - From the Bench to the Clinic*

nient to both patients and clinicians.

are formed directly against dietary gliadin [11].

in high demand to be developed.

**2. Lateral flow immunoassays**

through biopsy [1]. This process is highly invasive, time-consuming, and inconve-

Over the last several decades, researchers have found that the concentration of some certain antibodies circulating in celiac patients' body increased, and the detection of celiac disease can be achieved with the detection of these antibodies. In fact, the surface of mucosa represents the major targeted sites when foreign antigens attack the body [5]. Plausibly, 80% of all cells producing immunoglobulin (IgG) in the human body are in small bowel mucosa, which also produces the dimers of IgA [6]. Therefore, the antibodies of celiac disease among untreated patients are located in the mucosal surface [7], as extracellular deposit, some present in jejunal juice [8], and most in the intestine [9, 10]. For untreated celiac patients, the additional generation of antibodies leads to an increase of antibodies specific to celiac disease (IgA− class), most of which can be found in the circulating blood and some other bodily fluids. Among all the celiac-specific antibodies, anti-reticulin (ARA), anti-jejunal (JEA), endomysial (EMA), and tissue transglutaminase antibodies (tTG) are among the patients' own endogenous biomolecules that form as a result of immune response to antigen in the intestine, whereas anti-gliadin antibody (AGA) and deamidated gliadin peptide antibody (DGP-Ab)

Over the years, the detection of the celiac-related antibodies has shown promising results, and whole blood- or serum-based pathology tests are regularly used for screening for celiac disease. Typically, screening for celiac disease includes tests for identification of titers for AGA and/or anti-tTG antibodies, and most of these tests are based on enzyme-linked immunoassays (ELISA). Even though the method of ELISA can reach a high sensitivity and specificity, these tests cannot be used on their own in the process of celiac disease diagnosis. Furthermore, pathology tests are typically confined to centralized laboratories, where expert personnel is required, leading to slow- and high-cost detections. Thereby, it is not suitable for the use outside hospitals, such as clinical offices or home settings, leaving a high number of undiagnosed celiac cases, especially when their symptoms are not obvious or do not affect their normal life. Thus, simple and rapid detection methods are

Fast, accurate, and noninvasive early diagnosis methods and/or devices are needed to achieve the detection of celiac disease with high sensitivity and specificity, especially facing the rapid increasing number of celiac patients. Over the last decade, several point-of-care blood tests have been developed and applied for celiac diseases screening. The most prominent tests are Simtomax® Blood Drop system (Augurix SA, Switzerland) and Biocard™ celiac test (AniBiotech®, Finland), lateral flow immunoassays that detect anti-tTG and/or anti-deamidated gliadin peptide antibodies. Lateral flow test, also called lateral flow immunoassay or test strip, has been widely and commercially used in the rapid detection of many diseases and conditions, such as HIV, illicit drugs, and early pregnancy [12]. In the following sections, we will discuss and compare several commercial kits available as POCT devices for celiac disease. The principle of lateral flow test is outlined in the next section.

Lateral flow immunoassay is a simple immunochromatography technology that has successfully applied for rapid diagnostic testing [12, 13]. It typically made of nitrocellulose or paper-based porous membrane that makes it ideal to fabricate low-cost devices with little maintenance requirements. Porous membrane enables the separation, capture, and recognition of the target analytes. In addition, porous

**24**

*Schematic representation of lateral flow immunoassay in a capture format. Various important parts of the test are identified as sample, conjugate, and absorbent pads, nitrocellulose membrane with test and control lines.*

nature of the material facilitates movement of fluids, such as a whole blood, serum, or urine, by means of capillary action with no external force required.

There are several types of lateral flow assays available, but the most popular is the capture format. There are two types of capture: "sandwich" and competitive capture [13].

Overall, lateral flow immunoassay consists of four parts: sample pad, conjugate pad, nitrocellulose membrane (test line and control line labeled on it), and absorbent pad (also called wicking; **Figure 1**). Typically, fluid sample (blood, serum, urine, saliva) is added onto sample pad. Through the capillary action, the liquid moves to the conjugate pad, where preloaded recognition element (conjugated nanoparticles or colored reagent) is imbedded. The sample and the recognition reagent react commonly through antigen-antibody interaction. The sample together with the recognition element continues flowing within nitrocellulose membrane toward test and control lines. Depending on the type of a capture, sandwich or competitive, the test line would show a colorful line or disappear, respectively. Control line always shows colorful signal to indicate the correct functionality of the test. Absorbent pad function is to collect all the unreacted reagents as well as excess of liquids.

Lateral flow immunoassay for celiac disease is typically used to detect antibodies, such as anti-tTG, anti-DGP, and AGA antibodies from the whole blood or serum in a sandwich type of detection [14–18]. Preloaded reagent can be gold nanoparticles or dye conjugated to antigens, such as transglutaminase, deamidated gliadin peptides, and gliadin protein fragments. The detection of celiac disease-related antibodies will present as color test line that can be usually seen by the naked eye.

Lateral flow test or strip test is often used as a point-of-care test (POCT) due to its high specificity, visual color confirmation, and, especially, because of no additional instrumentation is required. In fact, most of the current commercial POCTs for celiac disease are based on lateral flow assay to detect antibodies. In the following section, we will discuss and make a comparison among commercial kits available together with the outlining principles of POCT device for celiac disease.
