The diagnostic criteria for nephrotic syndrome are as follows:

1. First, massive proteinuria, with a 24 - hour urine protein exceeding 3 grams.
2. Second, hypoalbuminemia, with albumin less than 30 grams per liter.
3. Third, severe edema.
4. Fourth, hyperlipidemia.

As long as massive proteinuria and hypoalbuminemia are present, the diagnosis can be established.

The cause of primary nephrotic syndrome is primary glomerular diseases. Primary nephrotic syndrome is divided into five pathological types, namely minimal change disease, mesangial proliferative glomerulonephritis, mesangiocapillary glomerulonephritis, membranous nephropathy, and focal segmental glomerulosclerosis.

A renal biopsy is required for patients with primary nephrotic syndrome to clarify the pathological classification because different pathological types have different prognoses and treatments. Among them, the prognosis of minimal change disease is relatively good, while that of mesangiocapillary glomerulonephritis is relatively poor.