Oh, what a groundbreaking revelation we have here! In a stunning display of scientific inquiry, researchers have bravely ventured into the world of rheumatoid arthritis (RA) to discover that—hold your applause—calprotectin levels in the blood and knee juice (a.k.a. synovial fluid) might just tell us something about inflammation. They rounded up 76 eager participants with creaky, cranky knees to play along.

These intrepid scientists measured everything but the kitchen sink: disease activity scores, X-ray evidence of joint party fouls, and a smorgasbord of blood markers including the ever-popular C-reactive protein and those trendy anti-citrullinated peptide antibodies (ACPA). They even counted the white blood cells in the synovial fluid for good measure—because, why not?

And lo and behold, serum calprotectin—our inflammatory tattletale—had a stronger correlation with inflammation than its synovial counterpart. It’s almost as if the blood is a good place to look for signs of systemic trouble! Who knew? But wait, there’s more: serum calprotectin was particularly chatty in patients with ACPA, suggesting that neutrophils might be gossiping about inflammation in these individuals.

But here’s the kicker: measuring calprotectin in the synovial fluid is about as useful as a chocolate teapot. That’s right, folks, it doesn’t seem to add any extra insight beyond what the blood test offers. So, next time you’re thinking about where to look for inflammation in RA patients with knee synovitis, remember: it’s all about the serum. Mind-blowing, I know.