It is well known that high blood levels of urea nitrogen or creatinine do not necessarily incriminate the kidney. Obstructive uropathy, heart failure, dehydration, diabetic and addisonian coma, among other extrarenal conditions, are frequent culprits, which give false-positive readings in regard to renal damage.
Less well appreciated is the fact that the converse may also be true and that normal blood urea nitrogen (BUN) and creatinine do not necessarily absolve the kidney from guilt. In the presence of dietary protein deficiency, these normal readings may give misleadingly false-negative results. Klahr and Tripathy,1 as reported in the October issue of the Archives of Internal Medicine, have observed normal or only slightly elevated nonprotein nitrogen (NPN) values in two patients after several days of anuria in the wake of acute renal failure. Both patients were in a poor state of nutrition.
These investigators report a comparative study of BUN and creatinine
MASKING BY MALNUTRITION. JAMA. 1966;198(3):313. doi:10.1001/jama.1966.03110160141047