Assessment of renal tubular function and damage and their clinical significance.

Abstract

Renal function is usually assessed by making some estimate of glomerular filtration rate (GFR). Renal damage is usually detected through an increase in the excretion of protein in the urine, which is usually taken as evidence of glomerular damage rather than tubular damage. Renal tubular function or damage is rarely specifically tested or looked for in routine practice because tubular dysfunction is rarely clinically important and is difficult to detect simply, and the generalised loss of tubular function in chronic renal diseases goes hand in hand with the loss of glomerular function and does not need to be assessed separately. During recent years, however, there has been a rapidly increasing interest in the detection of'.renal tubular damage and in the assessment of renal tubular function. There are three general reasons for this change of emphasis. One reason is an increasing clinical need for the detection of minor changes in renal function (tubular or glomerular). A second reason is that certain characteristics of the kidney and renal tubular function, some only recently defined, make it possible to devise tests which will detect very small changes in tubular function. The third reason is that increasingly simple techniques are available to measure the urine components that form the basis of these sensitive tests of tubular function. What has not been much emphasised, although it was for us a major reason for interest in the topic, is the concept that the renal tubular cell can be used as a sample cell for generalised cell damage with the likely advantage that lesser degrees of damage can be detected in the cells of the kidney than in cells of other organs of the body. The clinical need to detect lesser degrees of renal damage is based on the hope that it will be possible to identify patients at risk of progression to more serious damage in situations and at a time when treatment might prevent that progression. In addi­ tion, these more sensitive tests make it possible to study the relation between cause and effect (for