lowest FeNa I have ever seen

I was consulted on a patient with autoimmune hepatitis and acute kidney injury. The patient has ascites and was admitted with a small bowel obstruction.

I’m not sure if it is actually the lowest but it is remarkably low:

serum Na 147 mmol/L
serum Creatinine 1.77 mg/dL

urine Na <10
urine Cr 148

I assumed a urine sodium of 5 mmol/L

FENa= 0.04%

This is 4 molecules of sodium excreted for every 10,000 filtered. Amazing.