Bone Marrow Biopsies

Author: Pallavi Bollineni

A bone marrow biopsy is a routine procedure for the detection of a range of diseases, including blood cancers, severe anemias, and infections. Deep inside your bones is a spongy, gelatinous tissue called bone marrow. Although it is hidden from view, it’s often referred to as the “workhorse organ” since it’s considered a complex functional tissue and one of the largest organs in the human body, accounting for around 4-5% of total body weight. The bone marrow produces billions of new cells every day, including red and white blood cells and platelets. So, the health of blood heavily relies on the marrow, and analyzing it reveals specific issues that a regular blood test cannot. Beyond diagnosing diseases, the biopsy also helps doctors understand what stage of blood cancer the patient is going through and how well treatments like chemotherapy and transplants are working. The procedure is minimally invasive and generally considered very safe, and for decades it’s been the standard to examine the bone marrow, though newer imaging like PET-CT is starting to be utilized when needed. 

Figure 1; Credits: Cleveland Clinic

How A Bone Marrow Biopsy Works

A bone marrow biopsy usually involves two samples: the aspirate and a core biopsy. The aspirate is the liquid part of the bone marrow that’s drawn out through a needle. It is usually taken from the posterior iliac crest, the upper edge of the back of the hip bone (pelvis), which is the most common spot to take marrow samples. For the main part of the biopsy, a needle removes a solid piece of marrow from the back of the hip bone. The operation is done under anesthesia and sterile conditions. There is no specific sample size needed to complete the surgery, but anywhere from 0.5 to 1 cm is considered acceptable, and 2 to 3 cm is ideal. During the procedure, the patient lies on their stomach or side, and the doctor injects anesthesia and makes a small cut in the skin to insert the needle through the hard outer layer of bone until it reaches the marrow. A syringe is then used to pull out the liquid aspirate, which is briefly painful, and the sample is quickly spread onto glass slides before it can clot. For the core biopsy, the needle is moved to a new spot and pushed even further to get a solid piece of marrow. After collected, it’s placed in a preservative and sent to the lab to be analyzed. 

Figure 2; Credits: Peter Hutten-Czapski

Limitations & Risks

Even when the procedure itself goes well, the sample can still cause problems. If the aspirate is mixed with too much blood, it might not have enough marrow to analyze. In some patients who have scarring in the marrow, a condition called fibrosis, where the fibers replace the normal marrow tissue (see Fig.3). When this happens, liquid cannot be drawn out at all. This is known as a “dry tap.” The aspirate and core biopsy don’t always agree, and some abnormalities, like clusters of cancer cells, may be found in the core but not in the aspirate. Interpreting the samples can be difficult as well. For example, conditions like vitamin B12  deficiency or certain (Bone marrow biopsy showing scarring, a “dry tap”) abnormal even when no cancer is present, and for some diseases, doctors disagree on the initial diagnosis in around 20% of patients. Finally, because the needle only samples one small area of the hip bone, it can miss disease that is patchy or located elsewhere in the body.

Figure 3; Credits: Swachi Jain; Rashi Sharma (Bone marrow biopsy showing scarring, a “dry tap”)   

The Future of Bone Marrow Biopsies

Despite these limitations, bone marrow biopsies are still widely used to diagnose potential disease. In some cancers, imaging is now challenging the biopsy’s role as the standard test. PET-CT creates a three-dimensional image of the whole body and shows areas where cells are specifically active. Unlike a biopsy, it’s non-invasive and can examine the entire marrow, including disease far from the hip bone. In a study of DLBCL patients, PET-CT detected marrow involvement, which occurs when cancer cells or other abnormal cells spread, compared to only 38% for biopsy. Results like these have led some experts to recommend skipping a routine biopsy if a PET-CT scan is already positive. However, PET-CT is not an exact replacement. It exposes patients to an abundance of radiation, can confuse inflammation or infections for cancer, and can miss small amounts of disease or a smaller growing lymphoma in the marrow. It also can’t confirm disease under a microscope the way a biopsy can. Because of this, most researchers advise both tests to identify marrow disease. Researchers are also studying PET - radiomics, which uses computer analysis and machine learning to find patterns in scans that people might miss, and PET combined with MRI instead of CT could potentially spare patients the pain of a biopsy. 

Works Cited

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Jain, Swachi, and Rashi Sharma. "Laboratory Evaluation of Bone Marrow." StatPearls, StatPearls Publishing, 3 Mar. 2024, www.ncbi.nlm.nih.gov/books/NBK603716/. 

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Hutten-Czapski, Peter. “The Occasional Bone Marrow Biopsy : Canadian Journal of Rural Medicine.” Ovid, www.ovid.com/jnls/cjrm/fulltext/10.4103/cjrm.cjrm_64_22~the-occasional-bone-marrow-biopsy.