Tubular damage in patients with hypokalaemia

Severe hypokalaemia is occasionally associated with gross changes in renal tubular function. We have looked for lesser degrees of renal tubular damage in unselected patients with hypokalemia by measuring the urine excretion of total protein, albumin, the low molecular mass protein beta 2-microglobulin (B2M) and two enzymes, N-acetyl-glucosaminidase (NAG) and alanine aminopeptidase (AAP). The frequency of abnormal values for these tests separately (compared with matched patients without hypokalaemia) was 39-56%. Many patients had an abnormal value for more than one of the tests, but this was at least partly due to chance association rather than to an underlying common mechanism for the several abnormalities. The frequency of abnormal values was greatest in the patients with the lowest plasma potassium concentrations, but not all of these patients had abnormal values for even one of the tests. Repeated measurements during treatment with potassium supplements showed that the tubular damage resolved in some patients but more slowly than the hypokalemia. These results demonstrate that renal tubular damage is common amongst patients with hypokalaemia and is probably a consequence of the hypokalaemia in most of them. The measurements allow detection of patients whose tissues (at least the kidney) are adversely affected by the hypokalaemia, but the clinical usefulness of this information is yet to be established.