to the editor: Thanks to the authors for this clear and timely article. I would like to add a few words on benign hereditary nephritis, now known as thin basement membrane nephropathy.¹ In the late 1970s, I followed five generations totaling 207 patients with this condition in Lancaster and Chester Counties, Pa.; Cecil County, Md.; and Ashe County, N.C.² These patients had intermittent microscopic hematuria and a high but intermittent incidence of red blood cell casts. No evidence of progression of renal disease was found. Descendants of this group resided in at least 14 states.

For patients with microscopic hematuria who have not received a definitive diagnosis after a thorough workup before kidney biopsy, physicians should evaluate for a family history of recurring intermittent microscopic hematuria with intermittent red blood cell casts. Thin basement membranes are found in 5% to 9% of transplanted kidneys, but thin basement membrane nephropathy is found in less than 1% of the population. Thin basement membrane nephropathy and immunoglobulin A nephropathy are now considered common causes of asymptomatic hematuria after malignancy has been excluded.