Celiac Panel: Which Tests to Order Alongside for a Complete Workup

What a Celiac Panel Actually Measures

A standard celiac panel measures antibodies that the immune system produces in response to gluten exposure. The primary marker is tissue transglutaminase IgA (tTG-IgA), which carries a sensitivity of 93% to 98% and specificity above 95% for active celiac disease according to the American College of Gastroenterology (ACG) clinical guidelines [1]. Most labs bundle tTG-IgA with a total serum IgA level. That second value matters.

Roughly 2% to 3% of celiac patients have selective IgA deficiency, a rate 10 to 15 times higher than the general population [2]. When total IgA is low, tTG-IgA results become unreliable. A false negative follows. In these cases, IgG-based assays (deamidated gliadin peptide IgG or tTG-IgG) replace the standard test [3]. The American Gastroenterological Association recommends checking total IgA on every initial celiac screen for exactly this reason [3].

Some panels also include endomysial antibodies (EMA-IgA), which are highly specific (near 99%) but more expensive and operator-dependent. EMA confirmation is useful when tTG-IgA results fall in an indeterminate range (weak positive, typically 1 to 2 times the upper limit of normal).

A positive celiac panel does not end the workup. It starts it.

Iron Studies and CBC: The Most Common Deficiency Pair

Iron deficiency anemia is the single most frequent extraintestinal presentation of celiac disease, and in many patients it is the reason the celiac panel was ordered in the first place. A 2019 systematic review published in the American Journal of Gastroenterology found that iron deficiency affected up to 46% of adults with celiac disease at the time of diagnosis [4]. Proximal duodenal villous atrophy directly impairs iron absorption. The damage is anatomically specific.

Order a complete blood count (CBC) with differential alongside serum ferritin, serum iron, total iron-binding capacity (TIBC), and transferrin saturation. Ferritin alone is insufficient because it is an acute-phase reactant. A patient with active intestinal inflammation can have a "normal" ferritin while profoundly iron-depleted. The combination of low transferrin saturation (<20%) with elevated TIBC is more reliable in this context.

"Unexplained iron deficiency anemia, especially in young women or men without a clear bleeding source, should prompt celiac serologic testing," according to the ACG 2013 celiac disease guidelines [1]. This recommendation underscores why the pairing works in both directions: iron studies support celiac workup, and celiac panels explain refractory iron deficiency.

Thyroid Function: Autoimmune Overlap Is Not Rare

Celiac disease and autoimmune thyroid disease share HLA-DQ2 and HLA-DQ8 haplotypes, and they co-occur at rates that exceed coincidence. A meta-analysis of 27 studies in the Journal of Clinical Endocrinology and Metabolism reported that autoimmune thyroid disease (Hashimoto thyroiditis and Graves disease combined) was present in roughly 2% to 5% of celiac patients, compared with 1% to 2% in the general population [5]. The Endocrine Society notes this overlap as part of the polyautoimmune screening rationale.

Order TSH and free T4 at minimum. Adding thyroid peroxidase (TPO) antibodies is reasonable if the clinical picture includes fatigue, weight change, or family history of thyroid disease. Subclinical hypothyroidism in a newly diagnosed celiac patient can be missed if you rely on symptoms alone because the two conditions share nearly identical complaints: fatigue, constipation, hair thinning, brain fog.

The relationship runs both ways. The American Thyroid Association acknowledges that patients with established autoimmune thyroid disease carry an increased celiac risk, making bidirectional screening clinically justified [6].

Vitamin D and Bone Density: A Quiet Emergency

Celiac disease damages the proximal small intestine where calcium and vitamin D are absorbed. The clinical consequence is bone loss, and the numbers are striking. A study published in Alimentary Pharmacology and Therapeutics found that 50% to 80% of newly diagnosed celiac patients had 25-hydroxyvitamin D levels below 20 ng/mL [7]. Osteopenia or osteoporosis, confirmed by dual-energy X-ray absorptiometry (DXA), appeared in up to 75% of untreated adults with celiac disease [8].

Order 25-hydroxyvitamin D (not 1,25-dihydroxyvitamin D, which is less clinically useful for screening). If vitamin D is low or the patient has additional risk factors (postmenopausal status, glucocorticoid use, family history of osteoporosis), add serum calcium, intact PTH, and a DXA scan referral.

The British Society of Gastroenterology (BSG) guidelines on celiac disease explicitly recommend DXA scanning for all adults at diagnosis if they have low vitamin D, are postmenopausal, or have had symptomatic disease for more than one year [9]. This is not optional screening. It is part of the standard of care.

Bone recovery on a strict gluten-free diet takes 1 to 2 years for measurable improvement on DXA. Vitamin D and calcium supplementation during that window accelerates the process.

B12 and Folate: Distal Absorption Isn't Always Spared

Folate is absorbed in the proximal jejunum, which lies adjacent to the duodenum and is frequently involved in celiac mucosal damage. Folate deficiency affects approximately 20% of untreated celiac patients [10]. B12 absorption occurs in the terminal ileum, which celiac disease typically spares, so B12 deficiency is less common (roughly 5% to 8%) but not negligible [10].

A complete paired workup includes serum B12, serum folate, and methylmalonic acid (MMA) if B12 is borderline. The reason to measure both: macrocytic anemia from folate or B12 deficiency can coexist with microcytic anemia from iron deficiency, producing a normal-looking mean corpuscular volume (MCV) that masks two simultaneous deficiencies. The CBC looks deceptively normal. Only individual vitamin levels reveal the problem.

"Celiac disease should be considered in the differential of any unexplained B12 or folate deficiency, particularly when combined with iron deficiency," notes a review in Nutrients [10]. Testing all three (iron, B12, folate) together prevents the diagnostic tunnel vision of treating one deficiency while missing another.

Comprehensive Metabolic Panel: Liver and Electrolytes

Mild transaminase elevation occurs in 15% to 55% of celiac patients with active disease, a phenomenon called celiac hepatitis [11]. The World Journal of Gastroenterology published data showing that ALT and AST elevations up to 2 to 3 times the upper limit of normal were common in untreated celiac disease and typically normalized within 6 to 12 months of gluten withdrawal [11].

A comprehensive metabolic panel (CMP) captures hepatic aminotransferases, albumin (a proxy for protein status and malabsorption severity), electrolytes, and renal function. Low albumin at diagnosis suggests prolonged or severe malabsorption. Hypocalcemia on CMP, even before checking vitamin D, can be the first sign of impaired calcium absorption.

There is no separate order required. The CMP is routinely part of baseline labs, but clinicians ordering a celiac panel in isolation sometimes omit it. Do not.

Total IgA: The Gatekeeper Test

This point deserves its own section because missing it is the most common ordering error. A 2020 analysis in Clinical Gastroenterology and Hepatology found that approximately 7% of celiac screening panels were ordered without a concurrent total IgA, potentially rendering the tTG-IgA result uninterpretable [12].

Selective IgA deficiency, defined as serum IgA <7 mg/dL with normal IgG and IgM, affects 1 in 300 to 1 in 700 people in the general population. Among celiac patients, the prevalence is 2% to 3% [2]. If a patient has IgA deficiency, every IgA-based celiac test (tTG-IgA, EMA-IgA) is inherently unreliable. The lab may report "negative" when the patient actually has active celiac disease.

The fix is straightforward: order total IgA with every celiac panel. If total IgA is low, reflexively order tTG-IgG or deamidated gliadin peptide (DGP) IgG. Some reference laboratories offer this as an automatic reflex. Confirm with your lab whether this is built into the order set.

Type 1 Diabetes and Other Autoimmune Screening

The association between celiac disease and type 1 diabetes is well established. Between 3% and 10% of patients with type 1 diabetes also have celiac disease [13]. The American Diabetes Association (ADA) Standards of Care recommend celiac screening at the time of type 1 diabetes diagnosis and periodically thereafter [13]. The reverse pairing also matters: a new celiac diagnosis should prompt a fasting glucose or HbA1c if there is any clinical suspicion.

Other autoimmune conditions seen at increased frequency in celiac patients include dermatitis herpetiformis (the skin manifestation of celiac disease, present in 10% to 15% of cases), Sjögren syndrome, autoimmune hepatitis, and Addison disease. Screening for all of these at initial celiac diagnosis is not standard practice, but clinicians should maintain a low threshold for testing if symptoms arise.

The shared genetic architecture (HLA-DQ2 is found in over 90% of celiac patients) makes polyautoimmune clustering the norm rather than the exception for many celiac patients.

When to Repeat Labs After Diagnosis

Initial paired testing establishes the baseline. The follow-up cadence depends on clinical response to a gluten-free diet. The ACG guidelines recommend rechecking tTG-IgA at 6 to 12 months after starting gluten elimination, with the expectation that antibody levels should decline by at least 50% within the first 6 months and normalize by 12 to 24 months [1].

Nutritional labs (iron studies, B12, folate, vitamin D, CMP) should follow a similar schedule. Persistent iron deficiency after 12 months of strict gluten avoidance warrants investigation for ongoing gluten exposure (the most common cause) or an alternative diagnosis such as refractory celiac disease.

"Failure of tTG-IgA to normalize after 12 months of a gluten-free diet should prompt evaluation for ongoing gluten exposure or refractory celiac disease," states the ACG position statement [1].

Bone density reassessment via DXA should occur at 1 to 2 years if the baseline scan was abnormal. Thyroid function should be rechecked annually given the persistent autoimmune risk.

Building the Complete Order Set

The practical order set for a celiac panel workup, whether you are confirming a new diagnosis or evaluating a patient with suggestive symptoms, should include all of the following in a single blood draw:

Celiac-specific: tTG-IgA, total serum IgA (with reflex to DGP-IgG or tTG-IgG if IgA is low), EMA-IgA if tTG-IgA is equivocal.

Nutritional deficiency screen: CBC with differential, serum ferritin, serum iron, TIBC, transferrin saturation, serum B12, serum folate, 25-hydroxyvitamin D.

Metabolic and hepatic: comprehensive metabolic panel (includes ALT, AST, albumin, calcium, electrolytes).

Autoimmune overlap: TSH, free T4, TPO antibodies (if clinically indicated), fasting glucose or HbA1c (if type 1 diabetes risk factors present).

Referrals to consider: DXA scan for bone density, small bowel biopsy (remains the gold standard for histologic confirmation per ACG), and dietary counseling with a registered dietitian experienced in celiac disease management.

A single blood draw covers all the serologic tests. There is no reason to stage these across multiple visits for a patient already getting a needle stick for a celiac panel.