Giving urine biochemistry a second chance in acute kidney injury monitoring

Table 1 Sequential values of serum creatinine, diuresis, and urine biochemical parameters during acute kidney injury development and recovery¹

Parameter	Day1	Day2	Day3	Day4	Day5	Day6	Day7	Day8	Day9
sCr (mg/dL)	1.7	3.9	4.4	4.5	4.4	4.0	3.4	3.2	2.6
KU (mEq/L)	-	15.8	6.9	6.6	6.1	7.0	5.7	17.9	-
CrU (mg/dL)	-	105	49	45	47	47	35	62	-
KU/CrU ratio	-	0.15	0.14	0.15	0.13	0.15	0.16	0.29	-
Diuresis /24 hours (mL)	-	3380	5620	7100	8180	8300
2-hour excreted mass of creatinine (mg/hour)							227.5
2-hour measured CrCl (mL/min)							111.5

¹A 30-year-old, 100 kg, muscular male was admitted to the intensive care unit due to suspected intraoperative ischemic alterations detected in cardiac monitoring during an elective otorhinolaryngologic surgery. He developed postoperative Kidney Disease: Improving Global Outcomes stage 3 acute kidney injury that was attributed to the use of anti-inflammatory drugs. The very low urinary potassium (KU) was compatible with polyuria (KU decreases with urine output increase), and the very low KU/urinary creatinine (CrU) ratio indicated a disproportionate increase in CrU, which indicated an increased mass of excreted creatinine at day 7 after surgery (normal: 0.5-1.0 mg/kg/hour). The measured creatinine clearance (CrCl) on that same day demonstrated a recovered glomerular filtration rate but a still significantly increased serum creatinine (sCr). We concluded that renal recovery occurred around D2, but it took some days to equilibrate creatinine excretion with creatinine production (leading to sCr stabilization around 4.5 mg/dL) and, in the subsequent days, elimination of the exceeding mass of creatinine that rapidly accumulated in the muscular patient´s body (leading to decreases in sCr). The patient received 3-5 L of crystalloids every day to prevent dehydration. However, we hypothesized that polyuria could be the result of hydration in a patient with an already recovered glomerular filtration rate.

CrU: Urinary creatinine concentration; KU: Urinary potassium concentration; sCr: Serum creatinine; CrCl: Creatinine clearance.