Comparison of a simple and a standard method for inulin renal clearance

Existing creatinine-based equations overestimate glomerular filtration rate in Indians

BACKGROUND

Accurate estimation of glomerular filtration rate (GFR) is important for diagnosis and risk stratification in chronic kidney disease and for selection of living donors. Ethnic differences have required correction factors in the originally developed creatinine-based GFR estimation equations for populations around the world. Existing equations have not been validated in the vegetarian Indian population. We examined the performance of creatinine and cystatin-based GFR estimating equations in Indians.

METHODS

GFR was measured by urinary clearance of inulin. Serum creatinine was measured using IDMS-traceable Jaffe's and enzymatic assays, and cystatin C by colloidal gold immunoassay. Dietary protein intake was calculated by measuring urinary nitrogen appearance. Bias, precision and accuracy were calculated for the eGFR equations.

RESULTS

A total of 130 participants (63 healthy kidney donors and 67 with CKD) were studied. About 50% were vegetarians, and the remainder ate meat 3.8 times every month. The average creatinine excretion were 14.7 mg/kg/day (95% CI: 13.5 to 15.9 mg/kg/day) and 12.4 mg/kg/day (95% CI: 11.2 to 13.6 mg/kg/day) in males and females, respectively. The average daily protein intake was 46.1 g/day (95% CI: 43.2 to 48.8 g/day). The mean mGFR in the study population was 51.66 ± 31.68 ml/min/1.73m2. All creatinine-based eGFR equations overestimated GFR (p < 0.01 for each creatinine based eGFR equation). However, eGFR by CKD-EPICys was not significantly different from mGFR (p = 0.38). The CKD-EPICys exhibited lowest bias [mean bias: -3.53 ± 14.70 ml/min/1.73m2 (95% CI: -0.608 to -0.98)] and highest accuracy (P30: 74.6%). The GFR in the healthy population was 79.44 ± 20.19 (range: 41.90-134.50) ml/min/1.73m2.

CONCLUSION

Existing creatinine-based GFR estimating equations overestimate GFR in Indians. An appropriately powered study is needed to develop either a correction factor or a new equation for accurate assessment of kidney function in the Indian population.

Clinical benefits of using inulin clearance and cystatin C for determining glomerular filtration rate in HIV-1-infected individuals treated with dolutegravir

INTRODUCTION

Dolutegravir may inhibit creatinine transporters in renal tubules and elevate serum creatinine levels. We investigated the usefulness of glomerular filtration rate (GFR) measured using inulin clearance (Cin), creatinine clearance (Ccr), and estimated GFR based on both serum creatinine (eGFRcre) and serum cystatin C (eGFRcys).

PATIENTS & METHODS

HIV-1-infected Japanese patients with suppressed viremia and whose antiretroviral drug was switched to dolutegravir from other drugs were included (n = 108, Study 1). We compared eGFRcre and eGFRcys at the start and after 48 weeks of dolutegravir administration. For the patients providing consent, we measured Cin and Ccr (n = 15, Study 2). We assessed biases and accuracy and compared Cin with eGFRcre, eGFRcys, and Ccr.

RESULTS

There were no differences in serum cystatin C and eGFRcys between baseline and at 48 weeks. Moreover, eGFRcre was significantly less accurate (within 30% of measured GFR) than both eGFRcys and Ccr (40% accuracy compared to 93% and 93%, respectively). eGFRcys was significantly less biased than eGFRcre and Ccr (p < 0.0001, p = 0.00036, respectively). No significant difference between Cin and eGFRcys was observed. eGFRcys was significantly correlated with Cin (γ = 0.85, p < 0.0001).

CONCLUSIONS

eGFRcys provided the most precise estimate and most closely approximate Cin in HIV-1-infected Japanese patients with suppressed viremia treated with dolutegravir. We demonstrated clinical benefits of inulin clearance and eGFRcys. This is the first study performing inulin clearance for HIV-1-infected individuals and to show data for eGFRcys from a large cohort following a switch to dolutegravir from other antiretroviral agents.

Clinical impact of kidney function on presepsin levels

OBJECTIVE

Presepsin is highlighted as a diagnostic and prognostic marker of sepsis. Little information is available regarding the accurate association between presepsin levels and the degree of kidney function. We analyzed presepsin levels in patients with a glomerular filtration rate (GFR) in the categories G1 to G5, evaluated via inulin renal clearance test, and receiving hemodialysis (HD).

METHODS

Patients who were not receiving HD were included if they had undergone inulin renal clearance measurements for the accurate measurement of GFR (measured GFR), and patients who were receiving hemodialysis (HD) were included if they had anuria. Exclusion criteria were infection, cancer, liver disease, autoimmune disorders, or steroid or immunosuppressant use. GFR category was defined as follows; G1: GFR ≥ 90 ml/min/1.73 m2, G2: GFR = 60 to 90 ml/min/1.73 m2, G3: GFR = 30 to 60 ml/min/1.73 m2, G4: GFR = 15 to 30 ml/min/1.73 m2, G5: GFR ≤ 15 ml/min/1.73 m2.

RESULTS

Seventy-one patients were included. The median (IQR) presepsin values of patients in each GFR category were as follows: G1 + G2: 69.8 (60.8-85.9) pg/ml; G3: 107.0 (68.7-150.0) pg/ml; G4: 171.0 (117.0-200.0) pg/ml; G5: 251.0 (213.0-297.5) pg/ml; and HD: 1160.0 (1070.0-1400.0) pg/ml. The log-transformed presepsin values, excluding patients receiving HD, inversely correlated with the measured GFR (Pearson's correlation coefficient = -0.687, P < 0.001). The multivariate analysis revealed that measured GFR and hemoglobin levels significantly correlated with elevated presepsin levels.

CONCLUSION

Presepsin levels were markedly high in patients receiving HD, similar to values seen in patients with severe sepsis or septic shock. In patients who were not receiving HD, presepsin levels increased as GFR decreased. Thus, the evaluation of presepsin levels in patients with chronic kidney disease requires further consideration, and a different cutoff value is needed for diagnosing sepsis in such patients.

Extension of the Calvert formula to patients with severe renal insufficiency

PURPOSE

The Calvert formula was derived from the study among patients with glomerular filtration rates (GFRs) of 33-135 ml/min, and it remains unclear whether the formula can be used to calculate optimal and safe dosages of carboplatin in patients with severe renal insufficiency. We evaluated the utility of this formula in patients with severe renal insufficiency.

METHODS

For pharmacokinetic analysis, we studied nine adult Japanese patients with advanced cancer who had an estimated GFR of lower than 30 ml/min/1.73 m(2), as calculated by the Japanese equation for estimating GFR, or who were receiving hemodialysis. The dose of carboplatin was calculated with the Calvert formula, in which GFR was measured by inulin clearance or was assumed to be 0 in patients requiring hemodialysis. Hemodialysis was started 23 h after the end of carboplatin infusion.

RESULTS

Although there was a significant correlation between the estimated and measured carboplatin clearance, the estimated clearance was consistently higher than the measured clearance [mean prediction error ± standard deviation = 41.0 ± 26.3 %] in all seven patients with renal insufficiency (GFR, median 21.4, range 7.8-31.4 ml/min) and in the two hemodialysis patients. Actual areas under the concentration-time curve (AUC) (mg/ml min) were 5.4, 5.7, 6.2, and 9.0 for the four patients with a target AUC (mg/ml min) of 5; 5.7, 6.2, and 7.1 for the three patients with a target AUC (mg/ml min) of 4; and 5.1 and 8.7 for the two hemodialysis patients with a target AUC (mg/ml min) of 5. The measured clearance of carboplatin ranged from 23.0 to 51.3 ml/min in the seven patients not receiving hemodialysis. The pre-hemodialysis carboplatin clearance in the hemodialysis patients was 20.5 and 11.1 ml/min, respectively.

CONCLUSION

For adult patients with severe renal insufficiency, the Calvert formula causes carboplatin overdosing by overestimating the carboplatin clearance.

Individualizing pharmacotherapy in patients with renal impairment: the validity of the Modification of Diet in Renal Disease formula in specific patient populations with a glomerular filtration rate below 60 ml/min. A systematic review

Background

The Modification of Diet in Renal Disease (MDRD) formula is widely used in clinical practice to assess the correct drug dose. This formula is based on serum creatinine levels which might be influenced by chronic diseases itself or the effects of the chronic diseases. We conducted a systematic review to determine the validity of the MDRD formula in specific patient populations with renal impairment: elderly, hospitalized and obese patients, patients with cardiovascular disease, cancer, chronic respiratory diseases, diabetes mellitus, liver cirrhosis and human immunodeficiency virus.

Methods and Findings

We searched for articles in Pubmed published from January 1999 through January 2014. Selection criteria were (1) patients with a glomerular filtration rate (GFR) < 60 ml/min (/1.73m²), (2) MDRD formula compared with a gold standard and (3) statistical analysis focused on bias, precision and/or accuracy. Data extraction was done by the first author and checked by a second author. A bias of 20% or less, a precision of 30% or less and an accuracy expressed as P₃₀% of 80% or higher were indicators of the validity of the MDRD formula. In total we included 27 studies. The number of patients included ranged from 8 to 1831. The gold standard and measurement method used varied across the studies. For none of the specific patient populations the studies provided sufficient evidence of validity of the MDRD formula regarding the three parameters. For patients with diabetes mellitus and liver cirrhosis, hospitalized patients and elderly with moderate to severe renal impairment we concluded that the MDRD formula is not valid. Limitations of the review are the lack of considering the method of measuring serum creatinine levels and the type of gold standard used.

Conclusion

In several specific patient populations with renal impairment the use of the MDRD formula is not valid or has uncertain validity.

Risk of overestimation of kidney function using GFR-estimating equations in patients with low inulin clearance

BACKGROUND

Accurate estimation of the glomerular filtration rate (GFR) is very important in clinical practice. Although renal inulin clearance (Cin) is the gold standard for measuring GFR, the procedure for Cin measurement is complicated. Use of GFR-estimating equations has been increasing recently due to their simplicity. The objectives of the present study are to analyze the correlation between Cin and other GFR-estimating parameters and to investigate their clinical usefulness and limitation.

METHODS

Seventy-two Japanese patients were enrolled in this study. Cin was measured by the continuous infusion method. Serum creatinine (s-Cr), cystatin C, uric acid (UA), and hemoglobin (Hb) were measured. The Japanese formula of estimated GFR (eGFR) was as follows: eGFR (ml/min/1.73m(2) ) = 194 × s-Cr(-1.094) × Age(-0.287) × 0.739 (if female). The endogenous creatinine clearance test was also performed.

RESULTS

Levels of Cin were highly correlated with those of endogenous creatinine clearance (Ccr) (R(2) = 0.7585) and eGFR (R(2) = 0.5659). However, patients with lower Cin showed unexpectedly elevated levels of endogenous Ccr and eGFR. Moreover, the levels of eGFR tended to be unexpectedly increased in patients with low body surface area.

CONCLUSION

Although GFR-estimating equations are useful for estimating GFR accurately, they pose a risk of overestimation of kidney function in patients with decreased GFRor a poor physique.