Long-Read Sequencing

Comprehensive Analysis of Thalassemia Alleles (CATSA)

The World’s First IVD-Certified LRS Solution for Thalassemia

The Challenges of Comprehensive Thalassemia Detection

Thalassemia and hemoglobinopathy molecular testing is challenging due to the high sequence homology and variant complexity of the globin gene clusters. Conventional assays (including PCR-based testing and short-read NGS) cannot detect the full spectrum of clinically relevant variants, such as rare SNVs/InDels, large deletions or duplications, and complex structural variants. These limitations can result in stepwise testing, unresolved genotypes, missed carriers, and incomplete reproductive risk assessment.

Limitations of Conventional Testing Methods

Hematological Screening (CBC/CE)

Lacks sensitivity for carriers
Frequently misses silent carriers of α⁺-thalassemia, β⁺-thalassemia, and α-triplications

PCR-Based Testing

Limited to hotspot variants
While over a thousand of thalassemia variants exist, most PCR panels only cover a few dozen common mutations

Short-Read NGS

Struggles with the high homology (HBA1/HBA2, HBB/HBD)
Often misses large structural variants, miscalls variants, and cannot provide phasing information

Comprehensive Testing with CATSA

Comprehensive Analysis of Thalassemia Alleles (CATSA) is a long-read sequencing (LRS) assay designed to resolve the complexity of thalassemia and hemoglobinopathy variants in a single test.

Powered by PacBio HiFi long-read sequencing, CATSA detects more than 2,200 known thalassemia and hemoglobinopathy variants from curated in-house and public databases (e.g. HbVar, ITHANET), including rare variants, complex structural variants, and homologous recombination events. By consolidating multiple conventional assays into a single workflow, CATSA enables accurate detection and genotype interpretation for clinical and research applications.

CATSA has been endorsed as a diagnostic and screening tool by the expert consensus from Medical Genetics Branch of the Chinese Medical Doctor Association in 2025.¹

Comparison: CATSA vs. PCR and NGS

Variant Type

PCR Methods

Short-read NGS

CATSA

Common Deletions

✔

Other Deletions

✔

(Struggle if inside homology)

✔

Homologous Recombination

(e.g. α-triplicate)

(Some may be misinterpreted as deletions)

✔

Common SNVs/InDels

✔

Other SNVs/InDels

✔

(Susceptible to homology)

✔

Variant Phasing

✔

Performance Backed by Published Data

CATSA has been evaluated in 50+ peer-reviewed studies and multi-center clinical cohorts, demonstrating high accuracy and clinical utility in real-world scenarios.

20+ novel variants identified
100% accuracy²

A total of 1,759 blood samples with abnormal hemoglobin parameters were collected across 10 centers to compare CATSA with a standard PCR panel²

vs. NGS

CATSA has 100% accuracy compared to NGS miscalls in both HBA1/2 and HBB genes, driving a 2.28% improvement in overall detection yield

NGS (full-length HBA1/2 and HBB) and CATSA were simultaneously performed for 1,122 individuals in Hainan Province³

Versus a 13.7% NGS error rate (missed triplications and HKαα miscalls as deletions), CATSA delivered 100% accuracy across all α-thalassemia carriers

A total of 2,926 participants were retrospectively enrolled in Shanghai for carrier screening of 5 diseases using both commercial NGS carrier screening panel and LRS panels, with CATSA applied for thalassemia⁴

Prenatal Case Study - vs. PCR

In a multi-center retrospective study of 278 at-risk amniotic fluid samples, CATSA:

Outperformed PCR panel by corrected the results in 15 samples (5.4%)
Reclassified the predicted phenotype severity in 8 fetuses (2 cases from Trait to Intermedia, and 1 from Intermedia to Trait).

These insights directly influenced pregnancy management and counseling.⁵

Comprehensive coverage

Covers the most types of thalassemia and hemoglobinopathy variants

The new gold standard

Improves detection rate compared with routine test with >99.9% accuracy

Proven at scale

With 350,000+ cases and 50+ publications

When considering our send-out sequencing services:

Consultation: Contact our team for the most current test specifications.
Sample Preparation: Check sample types and shipment requirements to ensure high-quality results. Please check your local export regulations and logistics partners.
Submission: Contact Xcelom when placing an order. Include the completed Test Request and Consent Form, along with any required documents.

Sample Requirements

Peripheral Blood: 2 mL in EDTA tube

Dried Blood Spot (DBS): 3 spots, ≥ 8mm diameter each

Long-fragment gDNA

'**For prenatal cases, please include maternal sample for STR to exclude maternal contamination.

Transport Conditions

2-8℃, arrive within 72 hours

Testing Scope

637 Panel

Covers 637 variants associated with α-/β-thalassemia, and hemoglobinopathies (including sickle cell anemia), including:

HBA1/2 : 30 deletions, 4 homologous recombination, and 219 SNVs/InDels
HBB: 28 deletions, and 356 SNVs/InDels

Expanded Panel

Covers 2025 variants associated with α-/β-thalassemia, hemoglobinopathies, and hemoglobin variants, including:

HBA1/2 : 30 deletions, 4 homologous recombination, and 929 SNVs/InDels
HBB: 28 deletions, and 1034 SNVs/InDels

Comprehensive Panel

Covers variants associated with α-/β-thalassemia, hemoglobinopathies, and hemoglobin variants in HBA1/2, HBB, and HBD, including low-frequency mutations and uncertain significance associated with thalassemia and hemoglobinopathy

Turnaround Time (TAT)

15 working days

Xcelom Limited and Berry Genomics provide an end-to-end turnkey solution for labs wishing to conduct this test in-house.

Laboratory Setup: Full consultation
Workflow Integration: SOPs, IVD/RUO reagents, and staff training
Bioinformatics: Complete IVD/RUO software suite for sample management and automated report generation

Platform

PacBio Sequel IIe, Vega and Revio system

Sample Type

gDNA from dried blood spot, blood, buccal swab, and amniotic fluid

Test per Batch

1 - 384 Tests per SMRT Cell (Mixed Batching Supported)

Operation Time

~ 77 hours (Hand on time: ~10.5 hours)

Automation

Supported

Coverage

Targets full-length of HBA1/2, HBB-HBD, and HS-40 regions

Covers > 2,200 clinically relevant variants

The provided time is based on the PacBio Sequel IIe system and may vary across different labs and systems.

Resources

CATSA Brochure

References:

1. Consortium For The Application Of Single-Molecule Real-Time Sequencing For The Precision Medicine And Control Of Thalassemia, Group Of Clinical Genetics Medical Genetics Branch Of Chinese Medical Doctor Association, Wu L. Zhonghua Yi Xue Yi Chuan Xue Za Zhi. 2025;42(4):385-396.

2. Liang Q, Gu W, Chen P, et al. A More Universal Approach to Comprehensive Analysis of Thalassemia Alleles (CATSA). J Mol Diagn. 2021;23(9):1195-1204.

3. Huang R, Liu Y, Xu J, et al. Back-to-Back Comparison of Third-Generation Sequencing and Next-Generation Sequencing in Carrier Screening of Thalassemia. Arch Pathol Lab Med. 2024;148(7):797-804.

4. Li S, Hua R, Han X, et al. Targeted long-read sequencing facilitates effective carrier screening for complex monogenic diseases including spinal muscular atrophy, α-/β-thalassemia, 21-hydroxylase deficiency, and fragile-X syndrome. J Transl Med. 2025;23(1):307.

5. Liang Q, He J, Li Q, et al. Evaluating the Clinical Utility of a Long-Read Sequencing-Based Approach in Prenatal Diagnosis of Thalassemia. Clin Chem. 2023;69(3):239-250.