Cell Block Showdown: Finding the Best Way to Spot Granulomas
"A new study compares different cell block methods used with ThinPrep slides to detect granulomatous disease, focusing on effective diagnostic techniques."
When doctors need to figure out what’s going on in the mediastinum (the space in your chest between your lungs), they often use a technique called EBUS-TBNA. Think of it as a minimally invasive way to take samples for testing. This method is especially useful for detecting diseases like sarcoidosis, infections, lymphomas, and even cancer that has spread from other areas of the body.
EBUS-TBNA allows doctors to collect cells, which can then be prepared in a few different ways for examination. These include direct smears, liquid-based preparations like ThinPrep (TP), and cell blocks (CBs). Each method has its pros and cons, and labs often pick the one that works best for them based on their specific needs and resources. Cell blocks, in particular, can be really helpful because they allow for additional studies like immunohistochemistry, genetic testing, and molecular analysis—all crucial in the age of targeted therapies.
In a recent study, researchers set out to compare three different cell block preparation methods: plasma-thrombin, HistoGel, and a modified version of HistoGel called CellGel. They wanted to see which method, when used with ThinPrep slides, was most effective at finding granulomas (small clumps of immune cells) in samples taken from patients with mediastinal granulomatous disease. This research is all about finding the best way to improve diagnostic accuracy using minimally invasive techniques.
Granuloma Yield Across Cell-Block Methods
Laboratories use multiple cell-block preparation methods, and not all perform cell blocks alongside ThinPrep slides. In the comparison of plasma-thrombin, HistoGel, and CellGel methods for endobronchial ultrasound-guided transbronchial needle aspiration, plasma-thrombin and CellGel produced higher granuloma yields than HistoGel. Cell blocks generally showed more numerous and larger granulomas than ThinPrep slides. These findings highlight the importance of cell-block preparation for concentrating cellular material when evaluating mediastinal granulomatous disease.
Established Methods and Tradeoffs
A 2023 review examined the most common cell-block preparation methods used in cytology. It considered the advantages and disadvantages of each method as described in the literature and through the authors’ combined experiences. The review presents cell-block preparation as an established area with meaningful differences in method performance and practical limitations.
From Early Cell Blocks to Immunohistochemistry
The cell-block technique has been used in cytopathology for more than a century. The first reported use was by Bahrenburg in 1896, who processed large quantities of ascitic fluid from two patients into histologic sections. Later developments in immunohistochemistry renewed interest in cell blocks because they could help answer questions that morphological interpretation alone could not resolve. A Springer chapter recommends the thrombin-clot technique when a laboratory does not already have a satisfactory cell-block method.
Plasma-Thrombin vs. HistoGel vs. CellGel: Which Method Wins?
The study looked back at 264 specimens taken from 124 patients who had undergone EBUS-TBNA for suspected granulomatous disease. After the ThinPrep slide was made, any material left over was used to create a cell block using one of the three methods. The researchers then carefully counted and measured the granulomas on each preparation using digital software. Granulomas were defined as a cluster of at least five epithelioid histiocytes clumped together.
- Cell Blocks Excel: Granulomas were spotted on cell blocks in nearly 19% of cases, but only on ThinPrep slides in about 5%.
- More and Bigger: All three cell block methods found significantly more and larger granulomas compared to the ThinPrep slides.
- Plasma-Thrombin and CellGel Lead: Plasma-thrombin and CellGel methods seemed to yield more diagnostic material compared to HistoGel.
- Numbers Don’t Lie: On average, ThinPrep slides showed 4.0 ± 0.4 granulomas, while cell blocks showed 15.3 ± 1.1. Granuloma size averaged 119.2 ± 3.2 µm on ThinPrep slides versus 271.8 ± 7.3 µm on cell blocks.
Current Evidence and New Directions
In a study of mediastinal and hilar lymphadenopathy samples obtained by endobronchial ultrasound-guided transbronchial needle aspiration, sensitivity was 77.14% for cytology, 83.33% for histology, and 87.5% for combined evaluation. A 2025 report presented an internally validated protocol for alginate-encapsulated cell blocks used in routine pathology and cancer research studies. European laboratory practice remains variable: 113 of 399 laboratories prepared cell blocks from all cytology samples, while 42 of 399 processed only one specific sample and 244 of 399 used different combinations. Reviews describe cell blocks as useful across body fluids, fine-needle aspirates, and exfoliative samples, including applications related to personalized medicine.
Limits in Routine Use and Specificity
Cell-block preparations are not yet widely used for endobronchial ultrasound-guided transbronchial needle aspiration samples, and one study describes limited information about their contribution to diagnosis. Cytological assessment of lymph-node aspirates can demonstrate epithelioid histiocytes in a background of lymphocytes and plasma cells. However, the absence of giant cells makes that finding less specific for true granulomatous disease. These limitations show why cell blocks and cytology may not provide equivalent diagnostic certainty in every case.
Additional Yield Over Cytology
A comparison of endobronchial ultrasound-guided transbronchial needle aspiration cytology and cell blocks in adults with undiagnosed mediastinal lymphadenopathy found an overall additional cell-block yield of 3.2%. The additional yield was 1.8% for malignancy, 0% for tuberculosis, and 14.3% for sarcoidosis. The results indicate that the incremental value of cell blocks differed substantially by diagnostic category.
Why This Matters for You
This study highlights the importance of using cell block preparations in addition to ThinPrep slides when evaluating samples for granulomatous disease. The plasma-thrombin and CellGel methods appear to be particularly effective at capturing granulomas, potentially leading to more accurate diagnoses. This could mean fewer missed cases and better outcomes for patients undergoing evaluation for mediastinal granulomatous disease. Future research may explore whether these findings apply to other types of lesions and specimens, further refining diagnostic techniques in cytology.
Bringing Cell Blocks Into Practice
A prospective study evaluated how to establish, optimize, and implement the cell-block technique in routine diagnostic practice. Its stated purpose was to support immunocytochemistry. The work was conducted with approval from an institutional ethics committee, underscoring that introducing a laboratory technique involves both method development and formal clinical oversight.