Background:  Aging HIV-infected patients are at increased risk of renal dysfunction, rendering screening for renal function important. Estimated glomerular filtration rate (eGFR) is calculated with formulas using plasma creatinine or cystatin C (cysC), but their accuracy in HIV-infected patients is unknown. CysC may be affected by inflammatory conditions. We compared Cockcroft & Gault- (C&G), modification of diet in renal disease (MDRD) 4 and 6 parameter-, cysC-, and 24-hour urine-based eGFR with the “gold standard,” GFR-measured with [¹²⁵ I]-iothalamate (mGFR).

Methods:  We enrolled 19 patients in an ongoing randomized trial comparing continued effective first-line HAART with zidovudine/lamivudine to switching to tenofovir/emtricitabine, both plus either a NNRTI or a PI, were studied using baseline plasma and 24h urine samples and mGFR. mGFR was determined during continuous infusion of [¹²⁵ I]-iothalamate from timed urine collections, corrected for voiding inaccuracies. Precision and accuracy of the clearance estimations were calculated by plotting the difference between the estimations and the gold standard.

Results:  Of 19 patients, 18 were men, 15 Caucasian, 3 black and 1 Hispanic, mean (SD) age 46.0 (8.9) years, body mass index 23.8 (2.9) kg/m². Mean duration of HAART was 5.9 (2.4) years, mean baseline CD4-count was 579 (238) cells/mm³ and plasma HIV-1 RNA was <50 copies/mL in all patients. 17 patients were on a NNRTI- and 2 on a boosted PI-containing regimen. 2 patients had previously used indinavir, none had a history of renal insufficiency nor were hepatitis B virus/hepatitis C virus-positive. The mean (SD) mGFR, plasma creatinine and plasma cysC level were 134 (36) mL/min/1.73m², 80 (13) μmol/L, and 0.87 (0.22) mg/L, respectively. Of the total, 3 patients had mild renal dysfunction (stage 2). The mean (accuracy) and SD (precision) of the deviations from the mGFR for the various eGFR were as shown in the table. The MDRD-4-, MDRD-6- and cysC- eGFR underestimated the GFR. For all eGFR the precision was poor.

Conclusions:  In these patients with preserved renal function and suppressed HIV infection, the accuracy of the C&G- and the 24-hour urine-based eGFR was surprisingly good and reasonably estimated true GFR. Whether the inaccuracy of cysC-based eGFR may result from residual HIV-associated inflammation needs further research.