Cystatin C Falsely Underestimated GFR in a Critically Ill Patient with a New Diagnosis of AIDS

Table 1

Measured serum GFR surrogates including creatinine, cystatin C, and sulfamethoxazole concentrations.

Hospital day	Serum creatinine (mg/dL)	Cockcroft-Gault; creatinine clearance (mL/min)	Cystatin C (mg/L)	CKD-EPI (mL/min)	Sulfamethoxazole peak level (mcg/mL)
1	0.4	>120	—	—	—
7	<0.2	>120	—	—	136
8	<0.2	>120	1.50	36	—
9	<0.2	>120	1.42	39	—
14	0.2	>120	1.11	54	84

Hospital day 1 reflects the day of transfer from the outside facility to our center.
Target peak range for sulfamethoxazole in PJP is 100–150 mcg/mL. Both of the measured levels were documented while the dose of sulfamethoxazole/trimethoprim was 15 mg/kg/day of the trimethoprim component administered thrice daily as appropriate for therapeutic dosing in individuals with an estimated creatinine clearance of ≥30 mL/min.