Routine serologic tests in the differential diagnosis of the adult nephrotic syndrome.

From 1980 to 1985, we performed biopsies on 87 adults with nephrotic syndrome (NS). The patients were tested for whether serologic studies obtained routinely at biopsy added to clinical diagnostic accuracy. Using history, physical examination, complete blood cell count (CBC), chemistry panel, urinalysis, and urine creatinine and protein, four nephrologists each predicted whether the patient had primary NS (PNS) or secondary NS (SNS), and the most likely histopathologic entity. Six months later, each nephrologist used this information, with results of tests of sera for fluorescent antinuclear antibody (FANA), rheumatoid factor (RF), complement components, hepatitis B surface antigen (HBsAg), venereal disease research laboratory serology (VDRI), cryoglobulins and protein electrophoresis (SPEP), with an erythrocyte sedimentation rate (ESR) and protein electrophoresis of the urine (UPEP), to make identical predictions. Histopathology was established by renal biopsy. We analyzed the concordance between nephrologists' choices and biopsy results both before and after serologic tests were available with a kappa statistic. Preserology concordance was moderate (kappa = 0.52), and identical to postserology concordance (kappa = 0.51) for both PNS versus SNS and actual histopathology. Serologies were rarely abnormal without clinical suspicion. These results suggest routine serologic testing does not improve diagnostic accuracy in adult NS.

Complex response of epithelial cells to inhibition of Na+ transport by amiloride.

When toad urinary bladder or frog skin epithelia are treated with amiloride, short-circuit current (Isc), which represents the net active transepithelial Na+ transport rate from the apical to basolateral surface, decreases rapidly (2-5 s) to approximately 15-20% of control values and then slowly, over several minutes, continues falling toward zero. The contribution of this second phase of the decline is dependent on the transporting condition of the tissue before administration of amiloride. Attenuation of the second phase was observed if tissues were subjected to a period of transport inhibition. Tissues preincubated in 0 Na+ Ringer solution on the apical surface were returned to control Na+ Ringer, which caused an approximately 25% increase of Isc above control values. Immediate reapplication of amiloride caused Isc to decrease more rapidly than the previous exposure to values near zero, substantially reducing or eliminating the secondary slow decline. After long-term reincubation of tissues in control, 100 mM Na+ solution, another treatment with amiloride indicated that the magnitude of the secondary decline increased in frog skin but not in urinary bladder epithelia. We conclude that the effect of amiloride is complex and may cause additional effects besides simply blocking entry of Na+ into the apical membrane channel, and we suggest that regulatory mechanisms may be invoked in response to transport inhibition.