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In the era of precision medicine, a high-quality bone marrow biopsy specimen is the cornerstone for a correct diagnosis. However, many factors can affect the quality of the sample, and the most crucial aspect is the type of biopsy needle. Incorrect selection of the needle can lead to sample fragmentation, compression, dilution, or insufficiency, ultimately resulting in false negatives or misjudgments. This article will explore from the perspective of quality control how different types of bone marrow biopsy needles affect the accuracy of diagnosis.

1. Core Biopsy Needle Type: The Key Factor Determining the Completeness of the Tissue Strip

The purpose of a core biopsy is to obtain a complete and undamaged section of bone marrow tissue to assess the composition ratio of bone marrow cells, the degree of fibrosis, and the pattern of tumor infiltration, etc. Different types of core biopsies have a significant impact on this.

Tru-Cut type (manual cutting):

• Advantages: Theoretically, it can obtain the longest tissue strips (up to 2-3 cm), and the cutting process is relatively gentle, causing less damage to the cell morphology.
• Disadvantages: The operation technique requires extremely high skills. If the inner core is not fully embedded in the tissue when advancing it, or if the force applied when advancing the outer cannula is uneven, it is very likely to cause the tissue strips to be "broken" or "flattened." Moreover, for severely fibrotic bone marrow, manual cutting is often insufficient, leading to sampling failure.

Spring-type power biopsy needle (automatic cutting):

• Advantages: Its high-speed, standardized "launch-cut" mechanism almost eliminates human operational variations. Regardless of the softness or hardness of the bone marrow, it can obtain well-shaped and uniform tissue strips (usually 1-2 cm). Studies have shown that using the spring-type biopsy needle can increase the success rate of core biopsy from 70% of manual needles to over 95%.
• Disadvantages: The high-speed cutting may generate certain thermal effects or mechanical shear forces, causing slight damage to some fragile cells (such as lymphoma cells). Additionally, the length of the tissue strips obtained by this method is usually shorter than that of manual operation.

Vacuum-assisted biopsy needle:

This is a newer design. Negative pressure is applied inside the puncture needle to actively draw the tissue into the needle cavity before cutting. It can effectively solve the problem of difficulty in fixing bone marrow due to being too thin or fibrotic, especially suitable for dry tap cases. However, excessive negative pressure may also cause tissue collapse or cell fragmentation.

II. Type of Aspiration Needle: The "First Line of Defense" for Ensuring the Quality of Bone Marrow Fluid

Bone marrow fluid aspiration is used for cell counting, classification, flow cytometry, chromosome karyotype analysis, etc. The selection of the aspiration needle directly affects whether the sample is diluted by peripheral blood.

Side-hole needle vs. End-hole needle:

• End-hole needle: The traditional design makes it prone to aspirating blood from peripheral blood sinuses during aspiration, resulting in severe dilution of the sample and loss of representativeness for cytological examination.
• Side-hole needle: A hole is made on the side of the needle tip. During aspiration, it mainly sucks the substantive components within the medullary cavity, significantly reducing the risk of peripheral blood contamination. Therefore, for leukemia patients who need precise assessment of the original cell ratio, the side-hole needle is a better choice.

Needle diameter:

• Fine needle (22G): The trauma is minimal, but the aspiration resistance is high, it is prone to clogging, and the amount of liquid obtained is limited, making it difficult to conduct comprehensive molecular biology testing.
• Coarse needle (18G): The aspiration is smooth, and a sufficient amount of high-quality bone marrow fluid can be obtained. This is particularly suitable for scientific research projects that require a large number of cells for gene sequencing. However, the risk of bleeding increases accordingly.

III. Sample Processing and the Closed Loop of the Diagnostic Chain

Choosing the appropriate type of biopsy needle is just the first step. The subsequent sample processing is equally important.

• Core biopsy specimen: After extraction, it should be immediately placed in 10% neutral buffered formalin for fixation to prevent drying. The fixation time should not be too long to avoid affecting antigen retrieval. The decalcification step should be carried out carefully. Excessive decalcification will damage DNA and RNA, affecting subsequent FISH or NGS testing.
• Aspirate specimen: A slide and anticoagulation tube (EDTA or heparin) should be prepared immediately. The slide should be made evenly thick and thin to avoid artificial changes in cell morphology. The anticoagulation tube should be gently inverted and mixed to prevent clotting or hemolysis.

IV. Quality Control Indicators: How to Evaluate the Performance of Biopsy Needles?

Medical institutions should establish an internal quality control system and conduct regular evaluations of the performance of different biopsy needles.

• Core biopsy success rate: The proportion of tissue strips obtainable for diagnosis after a single puncture.
• Length and integrity of tissue strips: Average length, breakage rate, and compression degree score.
• Degree of bone marrow fluid dilution: Determined by calculating the ratio of the number of bone marrow granules in the smear to the proportion of peripheral blood cells.
• Incidence of complications: Including bleeding, infection, pain score, etc.
• Operation time: Total time from preparation to the specimen being removed from the body.

Conclusion

The type of bone marrow biopsy needle is the primary controllable variable affecting the quality of the sample. From the pursuit of "getting it" to the pursuit of "getting it well," clinicians and pathologists must closely collaborate. Based on the characteristics of the disease and the testing requirements, they should scientifically select the type of biopsy needle and strictly follow the standardized operating procedures. Only in this way can each precious bone marrow sample achieve the maximum diagnostic value.