Pathology/Lab Coding Alert

Focus molecular HLA typing.

Testing protocols for celiac disease diagnosis can be a complex challenge for coders. Look at the following case to help you master coding for the assays your lab may perform.

Define the Case

A clinician orders serology antibody testing for an 18-year-old patient with suspected celiac disease.

The lab evaluates a serum specimen for total IgA antibody using quantitative nephelometry. The patient IgA is elevated, indicating the need for the first-line IgA antibody marker for celiac disease: tissue transglutaminase antibody (tTGA). The quantitative result for this serum test shows a slightly elevated tTGA IgA of 8.2U/ml, indicating possible celiac disease.

Based on the low-positive tTGA IgA levels and the lab’s algorithm for celiac disease testing, the clinician orders a second IgA antibody marker: endomysial antibody (EMA). The EMA IgA test is negative, which reduces likelihood of a celiac diagnosis, but does not rule it out.

The clinician states that the patient may have self-imposed a gluten-restricted diet that could confound antibody test results, and maintains a strong suspicion of celiac disease. For that reason, the physician orders celiac-associated HLA-DQ testing.

The lab performs polymerase chain reaction amplification with sequence-specific oligonucleotide probes (PCR-SSO). The test involves high resolution DQA1 and DQB1 typing, identifying HLA-DQ2 allele groups DQA1*05:01/DQB1*02:01, 02:02; and HLA-DQ8 allele groups DQA1*03:01, 03:02, 03:03 and DQB1*03:02. The lab also reports loci DQA1 and DQB1 typing.

Find the Codes

For the serum IgA antibody titer, you should report 82784 (Gammaglobulin (immunoglobulin); IgA, IgD, IgG, IgM, each). “This is a quantitative nephelometry test that measures the level of IgA antibodies in the blood,” says William Dettwyler, MT AMT, president of Codus Medicus, a laboratory coding consulting firm in Salem, Ore.

tTGA IgA: Because the lab performs a quantitative tTGA IgA test on a serum specimen, you should list the test using code 83520 (Immunoassay for analyte other than infectious agent antibody or infectious agent antigen; quantitative, not otherwise specified). The test results were reported as 8.2U/ml, which is a quantitative finding.

Don’t miss: If the lab had performed a test that was positive or negative for tTGA IgA, you would have reported a different code, such as 83516 (Immunoassay for analyte other than infectious agent antibody or infectious agent antigen; qualitative or semiquantitative, multiple step method).

EMA IgA: A qualitative EMA IgA test looks for the presence or absence of endomysial antibody IgA using an indirect immunofluorescence assay (IFA) to stain a substrate. You may report the test as 86255 (Fluorescent noninfectious agent antibody; screen, each antibody). If the results had been positive, the lab may reflex to the titer and report an additional 86256 (… titer, each antibody).

Strongly positive antibody tests for tTGA and EMA IgA are highly specific for celiac disease, but the findings in this case can’t rule out the condition or specifically indicate the need for tissue biopsy. One possible confounding factor is the physician indication that the patient may have been consuming a gluten-free diet, which can make the IgA tests appear normal. That’s why the lab in this case recommends molecular testing that is not impacted by diet.

HLA-DQ: DQ2 and DQ8 are two serotype groups within the Class II HLA-DQ system that are strongly associated with celiac disease. DQ2 and DQ8 antigens are proteins formed from an alpha and beta strand, encoded on gene loci HLA-DQA1 and HLA-DQB1. Molecular testing allows typing of these loci, specifically identifying allele groups associated with celiac disease, such as HLA-DQ2 allele groups DQA1*05:01/DQB1*02:01, 02:02; and HLA-DQ8 allele groups DQA1*03:01, 03:02, 03:03 and DQB1*03:02.

Coding: Report the testing in this case as two units of 81382 (HLA Class II typing, high resolution (ie, alleles or allele groups); one locus (eg, HLA-DRB1, -DRB3/4/5, -DQB1, -DQA1, -DPB1, or -DPA1), each).

Here’s why: The molecular HLA testing the lab performs represents high resolution HLA typing according to CPT^® instruction, which states, “High resolution typing … is usually denoted by at least 4 digits (eg A*02:02…).

To choose between 81382 and 81383 (… one allele or allele group (eg, HLA-DQB1*06:02P), each), notice the text note following 81383: “When testing for the presence or absence of more than 2 alleles or allele groups at a locus, use 81382 for each locus.” Further, CPT^® Assistant May 2012; Volume 22: Issue 5 states, “When testing for one or two individual alleles … use the corresponding individual single-allele CPT^® code (… 81382 …). Because the lab performs high resolution testing for more than two alleles at two loci in this case, reporting 81382 for each locus is the best choice.

Caution: Some coders want to additionally report two units of 81376 (HLA Class II typing, low resolution (eg, antigen equivalents); one locus (eg, HLA-DRB1, -DRB3/4/5, -DQB1, -DQA1, -DPB1, or -DPA1), each) to report typing of DQB1 and DQA1 loci. “You should not list 81376 in addition to the more extensive procedure code 81382, because National Correct Coding Initiative (NCCI) lists 81376 as a column 2 code for 81382 for the same specimen,” Dettwyler says.