Researchers studied 178 patients with rheumatoid arthritis to understand why some develop sarcopenia—a condition where people lose muscle mass and strength. They found that a simple blood test called the Prognostic Nutritional Index (PNI), which measures protein levels and immune cells, could help doctors identify patients at risk. About one-third of the patients in the study had sarcopenia. The study suggests that patients with lower PNI scores are more likely to develop this muscle-wasting condition, especially if they’re older or have had arthritis for a long time.

The Quick Take

  • What they studied: Whether a simple blood test (PNI) that measures nutrition and inflammation could predict which rheumatoid arthritis patients would develop sarcopenia—a condition where muscles become weak and small.
  • Who participated: 178 patients with rheumatoid arthritis who were hospitalized in China between June 2023 and June 2025. About one-third of them had sarcopenia.
  • Key finding: Patients with lower PNI scores were significantly more likely to have sarcopenia. For every 1-point increase in PNI, the risk of sarcopenia dropped by 12%. Age, how long someone had arthritis, and inflammation levels also affected risk.
  • What it means for you: If you have rheumatoid arthritis, a simple blood test might help your doctor catch muscle loss early, before it becomes a serious problem. This could lead to earlier treatment and better outcomes. However, this finding needs to be confirmed in larger studies before it becomes standard practice.

The Research Details

This was a retrospective study, meaning researchers looked back at medical records from patients who had already been treated. They collected information from 178 rheumatoid arthritis patients seen at a hospital in China over a two-year period. The researchers measured a blood test called PNI, which combines two measurements: albumin (a protein in your blood) and lymphocytes (white blood cells that fight infection). They also recorded patient age, how long they’d had arthritis, inflammation markers, and whether they had sarcopenia. Sarcopenia was diagnosed using standard criteria that measure muscle mass and strength.

The researchers used statistical methods to figure out which factors were most important for predicting sarcopenia. They created a prediction model combining age, PNI score, disease duration, and inflammation levels, then tested how well this model could identify patients with sarcopenia.

This approach is practical because the PNI test is inexpensive, quick, and uses information doctors already collect routinely. It doesn’t require special equipment or procedures.

Understanding which patients are at highest risk for sarcopenia matters because muscle loss can lead to falls, disability, and reduced quality of life. If doctors can identify at-risk patients early using a simple blood test, they can intervene with nutrition support, exercise programs, or other treatments before serious muscle loss occurs. This study suggests that nutrition and inflammation status—both measured by PNI—are connected to sarcopenia risk in arthritis patients.

This study has several strengths: it used a clear definition of sarcopenia based on established guidelines, included a reasonable sample size (178 patients), and used appropriate statistical methods. However, there are limitations to consider: it was conducted at a single hospital in China, so results may not apply to other populations; it was a retrospective study, which means researchers couldn’t control all variables; and the study is relatively recent (2025), so findings haven’t been widely confirmed by other researchers yet. The study would be stronger if it included patients from multiple hospitals and different countries.

What the Results Show

Among the 178 rheumatoid arthritis patients studied, 56 patients (31.5%) had sarcopenia. When researchers analyzed the data, they found that lower PNI scores were strongly associated with sarcopenia. Specifically, for every 1-point increase in the PNI score, the risk of having sarcopenia decreased by 12%. This relationship remained significant even after accounting for other factors like age and inflammation.

Three other factors also independently increased sarcopenia risk: older age (each year of age increased risk by 7%), longer duration of arthritis (each year increased risk by 50%), and higher inflammation levels measured by C-reactive protein (each unit increased risk by 6%). When researchers combined all four factors (age, PNI, disease duration, and inflammation) into a prediction model, the model was very good at identifying which patients had sarcopenia, with a score of 0.92 out of 1.0 (where 1.0 is perfect).

These findings suggest that PNI is a useful marker for identifying arthritis patients at risk for muscle loss. The fact that it combines both nutritional status (albumin) and immune function (lymphocytes) makes it particularly valuable, as it captures two important aspects of the sarcopenia problem.

The study confirmed that sarcopenia is common in hospitalized rheumatoid arthritis patients, affecting nearly one-third of the group. The combination of multiple risk factors—age, disease duration, inflammation, and poor nutrition—appears to work together to increase sarcopenia risk. This suggests that patients with several of these risk factors need especially close monitoring. The study also demonstrated that a simple, cost-effective blood test could be used as a screening tool, which is important because many patients may not have access to more expensive muscle-imaging tests.

Previous research has shown that malnutrition and muscle loss are common problems in rheumatoid arthritis patients and are linked to worse health outcomes. This study builds on that knowledge by identifying a specific, simple blood test that could help predict which patients are at highest risk. The use of PNI as a marker is relatively new in arthritis research, though it has been used in other medical conditions. This study is among the first to thoroughly examine PNI’s usefulness for identifying sarcopenia in arthritis patients.

Several important limitations should be considered: First, this was a single-center study at one hospital in China, so results may not apply to patients in other countries or healthcare settings. Second, it was a retrospective study looking at past records, which means researchers couldn’t control all variables or confirm cause-and-effect relationships. Third, the study included only hospitalized patients, who may be sicker than arthritis patients in general. Fourth, the study is very recent and hasn’t been confirmed by independent researchers yet. Finally, while the prediction model performed well in this group, it needs to be tested in different populations to confirm it works reliably.

The Bottom Line

For rheumatoid arthritis patients: Ask your doctor about checking your PNI score as part of routine blood work, especially if you’re older or have had arthritis for many years. Focus on adequate protein intake and work with a nutritionist if possible. For healthcare providers: Consider using PNI as a screening tool to identify arthritis patients at risk for sarcopenia, and consider early intervention (nutrition support, physical therapy) for high-risk patients. Confidence level: Moderate—this is promising research, but larger studies in different populations are needed before making this standard practice.

This research is most relevant to: people with rheumatoid arthritis, especially those over 50 or who have had arthritis for many years; rheumatologists and primary care doctors treating arthritis patients; and nutritionists working with arthritis patients. People with other types of arthritis or those without arthritis should not assume these findings apply to them, as this study focused specifically on rheumatoid arthritis.

If your doctor identifies you as high-risk based on PNI and other factors, improvements in nutrition and muscle strength typically take 8-12 weeks of consistent effort to become noticeable. However, preventing further muscle loss can begin immediately with dietary changes and appropriate exercise.

Want to Apply This Research?

  • Track weekly protein intake (target: 1.0-1.2 grams per kilogram of body weight) and log any blood test results showing albumin and lymphocyte counts. Users can input their PNI score when available and monitor trends over time.
  • Set a daily reminder to consume adequate protein at each meal (aim for 20-30 grams per meal). Log resistance exercises or strength-training activities 2-3 times weekly. Users can set goals to maintain or improve muscle mass and track progress with simple measurements like grip strength or ability to perform daily activities.
  • Review PNI scores every 3 months if available from blood work. Track changes in muscle strength, energy levels, and ability to perform daily activities. Monitor inflammation markers (CRP) if your doctor orders them. Create a trend chart showing how nutrition, exercise, and inflammation markers change together over 6-12 months.

This research is informational only and should not replace professional medical advice. The findings are based on a single-center study in China and have not yet been widely confirmed by other researchers. If you have rheumatoid arthritis or concerns about muscle loss, consult with your rheumatologist or primary care doctor before making any changes to your diet, exercise routine, or treatment plan. The PNI test is not yet a standard diagnostic tool for sarcopenia and should only be used as recommended by your healthcare provider. Individual results may vary based on your specific health situation.