The most common test for lymphedema is the circumferential measurements taken along the hand, wrist, forearm, and upper arm at regular intervals. These measurements should be taken in the same places every time. Tape measures are widely available, inexpensive, and easy to use. However, your doctor or lymphedema therapist might use some of the following tests as well. These can be helpful not only for diagnosing lymphedema, but also monitoring its response to treatment.
- Optoelectronic limb volumeter (also called infrared perometry): This technique uses an infrared optical electronic scanner to calculate the volume of the affected arm, which is then compared to the other arm. You would place each arm into a large frame that sends infrared light beams inward from different angles. A computer then uses the resulting information to calculate arm volume.
- Water displacement: Water displacement isn’t used all that much anymore, mainly due to mess and inconvenience, but you might encounter it if you take part in a research study on lymphedema. You’d place each arm into a large cylinder of water and then any water that is pushed out is measured. Your therapist looks to see if the affected arm displaces more water than the other arm, which suggests larger volume.
- Bioimpedance scanning (BIS): Instead of measuring the volume of the arm, bioimpedance scanning detects the amount of fluid in the arm. The scanning device passes a small, painless electrical current through the limb and measures resistance to the current. Measurements are taken all the way up and down the arm. The higher the fluid content in the spaces between the tissues (also known as interstitial fluid), the lower the resistance. It’s thought that BIS is most useful when there are early changes in the arm associated with lymphedema, even before any symptoms become apparent.
- Tonometry: A tonometer is a device pressed into the skin to measure the amount of force required to make an indent in the tissue. The resulting measurement can help gauge the degree of firmness or fibrosis (tissue scarring) under the skin — a consequence of worsening lymphedema. However, the accuracy of tonometry can vary widely depending on the skill of the doctor or therapist using it. The original tonometers were mechanical devices with dial faces, but these are no longer in production. Newer electronic tonometers give digital readings. It’s thought that these electronic tonometers will be more accurate and easier to use, but they’re still under investigation in clinical trials.
- Imaging studies: Imaging studies such as Doppler ultrasound, MRI, and/or CT scans are most often used to rule out other problems that could be causing the lymphedema, such as a blood clot or a recurrence of the cancer. However, MRI and CT scans may occasionally be used to evaluate soft tissue for lymphedema-related changes. Another imaging test you might encounter is lymphoscintigraphy. This test involves injecting a radioactive substance into the hand or forearm, where it gets taken up by the lymphatic system. Then, a scanner or probe is used to follow the movement of this substance on a computer screen, providing information about how the lymph vessels and nodes are working.
More research is needed before we’ll know which test (or tests) is most reliable for diagnosing lymphedema. Don’t worry if your doctor or therapist can’t offer you one of the “high-tech” tests, such as infrared perometry or bioimpedance scanning. We don’t yet know whether these offer any real advantage over tape measurements. Also, the symptoms you report will play a very important role in making the diagnosis, as will the skill and experience of your lymphedema therapist. Andrea Cheville, MD, associate professor of physical medicine and rehabilitation at Mayo Clinic, suggests keeping a diary of symptoms that you can share with your lymphedema therapist.