Why periorbital swelling is first sign in nephrotic syndrome?

Periorbital swelling is often the first sign of nephrotic syndrome due to the loss of proteins, particularly albumin, through the kidneys, leading to low serum albumin levels (hypoalbuminemia). This decrease in oncotic pressure causes fluid to leak into the interstitial spaces, particularly noticeable in areas like the face and around the eyes. Additionally, the kidneys' impaired function can lead to fluid retention, further contributing to swelling. As a result, periorbital edema frequently becomes one of the earliest visible indicators of this condition.