The loin pain-hematuria syndrome occurs when glomerular hematuria occurs in conjunction with renal colic, in the absence of glomerulonephritis or a worsening of renal function. It is not a common disorder, though appears to be more common in women than in men. It appears to lie along the same continuum as thin basement membrane disease, as a substantial number of patients with loin pain-hematuria syndrome who undergo biopsy demonstrate irregularities (either too thick or too thin) in the glomerular basement membrane; in thin basement membrane disease, however, there does not seem to be a predilection for females and hematuria is typically painless. Approximately 20% of patients with suspected loin pain-hematuria syndrome who undergo biopsy are subsequently found to have IgA deposits–thus biopsy is warranted if the diagnosis of loin-pain hematuria syndrome is suspected. The pathophysiology of loin pain-hematuria syndrome is postulated to be based on irregular basement membranes, which will occasionally rupture and result in glomerular bleeding. When the bleeding is significant enough, it could conceivably result in swelling of the renal capsule and resultant pain. A decent review can be found in this 2006 KI article.