Celiac Disease

Indications for Testing

• Children and adolescents (ESPGHAN, 2012)

  • Who have unexplained
    • Gastroenterological symptoms
    • Poor growth
    • Delayed puberty
    • Iron deficiency anemia
    • Abnormal liver testing
  • Who have one of the following risks for celiac disease (CD) (even if asymptomatic)
    • Autoimmune disorders – diabetes mellitus type 1, autoimmune thyroiditis, autoimmune liver disease
    • At risk genetic syndromes – Down syndrome, Turner syndrome, Williams syndrome
    • First-degree relatives with CD
    • Selective IgA deficiency
• Adults

  • Who have unexplained
    • Gastrointestinal symptoms (diarrhea, abdominal pain, bloating)
    • Unexplained iron deficiency
    • Dermatitis herpetiformis
    • Recurrent aphthous stomatitis
    • Early-onset osteoporosis
    • Delayed puberty/unexplained short stature
    • Alopecia areata
  • Who have one of the following risks for CD (even if asymptomatic)
    • Family history of CD
    • Syndromes associated with risk for CD (eg, Down syndrome, Turner syndrome)
    • Autoimmune disease associated with CD (eg, diabetes mellitus type 1, thyroid or adrenal disease)
    • Selective IgA deficiency

Criteria for Diagnosis

• Positive tTG IgA (ACG, 2013) and/or EMA IgA serologic test (ESPGHAN, 2012)
• Biopsy consistent with CD in individuals with normal serum IgA levels
• tTG IgA or DGP and biopsy, with HLA-DQ genotyping only in event of biopsy/serology disagreement (WGO, 2016)
• CD may be confirmed without the need for biopsy in symptomatic individuals with high levels of CD-specific antibodies (10 x upper limit of normal) who are HLA-DQ2 or HLA-DQ8 positive (ESPGHAN, 2012)
• Complete resolution of clinical symptoms and/or a seronegative response following a gluten-free diet
  • Gluten rechallenge not necessary except in patients who did not have initial biopsy or had an uncharacteristic biopsy

Laboratory Testing

• Celiac disease tests and characteristics

  Test	Characteristics	Limitations
  Celiac Disease Reflexive Cascade	Preferred reflex screening test for celiac disease (CD) diagnosis Depending on initial results from IgA screening, one or more of the following tests may be added for clinical interpretation Tissue transglutaminase antibody, IgA Tissue transglutaminase antibody, IgG Endomysial antibody, IgA by IFA Deamidated gliadin peptide (DGP) antibody, IgA Deamidated gliadin peptide (DGP) antibody, IgG Celiac disease dual antigen screen
  Celiac Disease Dual Antigen Screen with Reflex	Acceptable single screening test for CD Reflex pattern – positive screen results reflex to IgA and IgG antibody testing for tTG and DGP	More expensive than tTG testing
  Tissue Transglutaminase (tTG) Antibody IgA Tissue Transglutaminase (tTG) Antibody IgG	Recommended single screening test for CD IgA testing recommended first to identify IgA deficiency prior to choosing tTG test Use tTG IgA in individuals who are IgA-competent; use tTG IgG in individuals who are IgA-deficient Confirmation by EMA may be necessary for low to moderate levels of tTG antibody Testing for DGP antibodies may also increase sensitivity for CD, particularly in children <2 yrs	May be less reliable in children <2 yrs tTG antibodies may be present despite undetectable levels of IgA
  Deamidated Gliadin Peptide (DGP) Antibody, IgA Deamidated Gliadin Peptide (DGP) Antibody, IgA	Acceptable single screening test for CD IgA testing recommended first to identify IgA deficiency prior to choosing DGP test May be considered in children <2 yrs if tTG or EMA negative Higher sensitivity/specificity than conventional antigliadin antibody (AGA) tests	May be present in the absence of  tTG IgA antibodies
  Endomysial Antibody, IgG Endomysial Antibody, IgA by IFA	Acceptable single screening test for CD IgA testing recommended first to identify IgA deficiency prior to choosing EMA  test High clinical specificity with good positive predictive value for active CD	More labor intensive  and expensive than tTG or IgA/ IgG testing
• Initial testing
  • Serum IgA level by nephelometry – determination of IgA levels prior to antibody testing is recommended; if patient is IgA deficient, all serologic testing must be performed using IgG tests to prevent false-negative antibody results
    • IgA level ≥7.0 mg/dL but below age-matched range – order Celiac Dual Antigen Screen with Reflex (see table above for components and characteristics)
      • Celiac Dual Antigen Screen with Reflex test results

        Celiac Disease Dual Antigen Screen with Reflex Test Results
        Normal	Celiac disease unlikely
        Positive or equivocal	Consider HLA genotyping (refer to Genetic testing section)
    • IgA <7.0 mg/dL – order tTG IgG and DGP IgG
      • Consider evaluation for immunoglobulin deficiency if IgG is normal – IgA deficiency may accompany other immunoglobulin deficiencies
      • Note – infants may present with transient suboptimal levels of IgA and/or IgG levels, which may not be related to immune deficiency
      • tTG IgG and DGP IgG test results

        tTG IgG and DGP IgG Test Results
        Normal	Celiac disease unlikely
        Positive or equivocal	Consider HLA genotyping (refer to Genetic testing section)
    • IgA level normal (age-matched range) – order tTG IgA
      • tTG IgA test results

        tTG IgA Test Results
        High-positive tTG IgA (≥41 U/mL)	Celiac disease (CD) likely; consider HLA genotyping (see Genetic testing section)
        Weak-moderate positive tTG IgA (4-40 U/mL)	Order EMA IgA by IFA, DGP IgA, HLA genotyping
        EMA and/or DGP negative; HLA positive	Perform biopsy (see Histology section)
        EMA and/or DGP positive, HLA negative	Likely false-negative HLA genotyping test; consider biopsy to confirm or rule out CD
        EMA and/or DGP positive, HLA positive	CD confirmed
        EMA and DGP negative; HLA negative	Likely false-positive anti-tTG test
        Negative tTG IgA (≤3 U/mL)	CD unlikely Exclude history of gluten-free diet or immunosuppressive drug (causes false-positive results) Consider HLA genotyping (in light of age and associated diseases) – refer to Genetic Testing section
• Genetic testing

  • HLA genotyping
    • HLA-DQ2 (encoded by HLA-DQA1*05 and HLA-DQB1*02) and HLA-DQ8 (encoded by HLA-DQB1*03:02)
      • DQ2
        • Present in >90% of individuals with celiac disease (CD); presence does not confirm CD
        • Found in 20-30% of general population
      • DQ8
        • Present in ~5-10% of individuals with CD
        • Found in 10% of general population
      • Absence virtually excludes CD
      • Not necessary for routine laboratory evaluation of CD due to low positive predictive value
      • May be indicated in individuals at risk for CD or individuals who are repeatedly seropositive but biopsy negative
      • Biopsy can be avoided if IgA anti-tTg >10x manufacturer's cutoff, confirmed by EMA in a different blood sample, and HLA testing is positive (ESPGHAN, 2012)

• Other testing
  • F-actin IgA antibody by ELISA
    • Presence of anti-actin antibodies in biopsy-confirmed CD patients may indicate intestinal villus atrophy – more severe form of disease expected
    • Should be ordered only in patients with confirmed CD by biopsy

Histology

• Duodenal biopsy – gold standard for CD diagnosis
  • 4-5 samples preferred to increase probability
    • ≥1 from the bulb and ≥4 from the second and third portion of the duodenum (ESPGHAN, 2012)
  • Patient must be on a gluten-containing diet at time of biopsy
• Intestinal damage is indicated by modified Marsh classification of histologic findings in CD (Oberhuber) or simplified system classification (Corazza, Roberts, Ensari)

Prognosis

• Anti-actin IgA (F-actin)
  • Levels correlate with severity of mucosa damage
  • May indicate moderate to severe disease – lacks specificity

Differential Diagnosis

• General differential based on clinical presentation
  • Irritable bowel syndrome
  • Inflammatory bowel disease
  • Infectious
    • Giardia
    • Cryptosporidium
    • Mycoplasma tuberculosis
  • Common variable immune deficiency
  • Malabsorption
  • Colorectal cancer
  • Malnutrition
  • Wheat allergy
  • Nongluten food hypersensitivity
  • Nonceliac gluten sensitivity
  • Microscopic colitis
  • Eosinophilic gastroenteritis
  • Intestinal lymphoma
  • Pancreatic insufficiency
  • IgA deficiency
  • Small intestinal bowel overgrowth
• Villous atrophy on biopsy
  • Tropical sprue
  • Whipple disease
  • Small intestinal bowel overgrowth
  • Hypogammaglobulinemic sprue
  • Drug-associated enteropathy
  • Lactose intolerance
  • Crohn disease
  • Autoimmune enteropathy
  • Refractory sprue
  • Collagenous sprue
  • Radiochemotherapy
  • Graft-versus-host disease
  • Nutritional deficiencies
  • Enteropathy-induced T-cell lymphoma
• Lymphocytic duodenosis
  • Helicobacter pylori
  • Medication effects
  • Small intestinal bowel overgrowth
  • Systemic autoimmune disorders
  • Intestinal lymphoma
  • Nonceliac gluten sensitivity