Correspondence

Metabolic Mimicry -- Renal Failure with Normal Renal Function

N Engl J Med 1994; 331:1778December 29, 1994

Article

To the Editor:

Diet is known to affect serum creatinine and urea nitrogen,1 but dietary variations are not usually considered in the differential diagnosis of elevated serum creatinine and urea nitrogen concentrations. I report an instance in which an unusual diet caused such an elevation, simulating chronic renal failure.

A 50-year-old asymptomatic woman who was apparently healthy was found during a routine medical checkup to have a serum creatinine concentration of 1.8 mg per deciliter (160 μmol per liter) and a serum urea nitrogen concentration of 35 mg per deciliter (12.4 mmol per liter). The physical examination was normal. She weighed 55 kg (121 lb). The serum concentrations of electrolytes and calcium were normal, as were the results of urinalysis, microscopical analysis of the urine, and intravenous urography. Histologic analysis of a renal-biopsy specimen containing 29 glomeruli revealed no abnormalities. Three months later, the serum creatinine concentration was 2.4 mg per deciliter (210 μmol per liter), and the serum urea nitrogen concentration was 41 mg per deciliter (14.6 mmol per liter). Urinary creatinine excretion was extremely high -- 4.6 g per 24 hours (41.0 mmol per 24 hours) -- and creatinine clearance was 148 ml per minute per 1.73 m² of body-surface area.

Because of the extremely high creatinine excretion, the patient was asked about her diet. She explained that it consisted of fresh fruit, raw vegetables, and approximately 2000 ml of broth daily, which she consumed at regular intervals. The broth was prepared by adding water to 4 kg (9 lb) of meaty bones, simmering the mixture for 10 hours, and then decanting the broth. The average creatinine and protein concentrations of two samples of the broth were 2.2 g per liter (19.5 mmol per liter) and 67 g per liter, respectively. Various laboratory measurements were made while the patient was ingesting this diet and after broth had been omitted for two days, and the results are shown in Table 1Table 1Laboratory Measurements Made While the Patient Was Following Her Usual Diet and Two Days after Broth Had Been Omitted from the Diet..

The high creatinine content of the broth resulting from prolonged heating of meat2 led in this patient to excessive ingestion of creatinine, which was reflected by the large reduction in urinary creatinine excretion when broth was not consumed. Since the serum creatinine concentration is dependent on the amount of creatinine ingested as well as the glomerular filtration rate and the rate of endogenous creatinine production,3 the patient's elevated serum creatinine concentration is well explained.

This case report is a pertinent reminder that factors other than the glomerular filtration rate affect serum creatinine and serum urea nitrogen.

Bernard F. Jones, M.B., B.S.
John Hunter Hospital, Newcastle, NSW 2310, Australia

3 References

1. 1

   Jacobsen FK, Christensen CK, Mogensen CE, Heilskov NS. Evaluation of kidney function after meals. Lancet 1980;1:319-319
   CrossRef | Web of Science | Medline

2. 2

   Macy RL Jr, Naumann HD, Bailey ME. Water-soluble flavor and odor precursors of meat. 5. Influence of heating on acid-extractable non-nucleotide chemical constituents of beef, lamb and pork. J Food Sci 1970;35:83-87
   CrossRef | Web of Science

3. 3

   Levey AS, Perrone RD, Madias NE. Serum creatinine and renal function. Annu Rev Med 1988;39:465-490
   CrossRef | Web of Science | Medline