The clinical utility of Cystatin C in assessing renal function among HIV-positive patients on antiretroviral therapy at Mildmay Uganda
Background: In
clinical practice, measurement of glomerular
filtration (GFR) rates is the gold standard for assessing renal function. Extra
renal factors affecting creatinine concentration, the most widely used molecule
in GFR estimation limit its efficiency. Use of exogenous substances e.g. inulin
to measure GFR is not possible due to cost and complexity. Cystatin C has been
proposed as a potential renal function marker but its use in HIV-Positive patients has not been well evaluated. The study was
carried out to assess
the clinical utility of Cystatin C based prediction
equation in determining renal function among HIV-positive infected individuals.
Methods: A cross sectional
study was carried out on 914 HIV-positive adults (≥18 years) on ART attending
Mildmay Uganda for care and treatment between January to March 2015. Serum Cystatin
C was measured by a quantitative sandwich enzyme immunoassay using the particle
enhanced immunoturbidimetric assay. Creatinine was analyzed using enzymatic
Creatinine PAP method. Using the results of the eGFR by creatinine as reference
method, the sensitivity, specificity and positive/negative predictive values
and likelihood ratios of Cystatin C were calculated.
Results: Of the 914
participants 626 (68.5%) were females and 288 (31.5%) were males. Median age in
the study was 38.4years (IQR 31 - 45). Median weight was 61.5 (IQR 52 - 70). Mean
Cystatin C (mg/L) concentration was 0.8mg/L. Means and standard deviation of
the main blood chemistries were Serum Creatinine 77(31.8), Serum Cystatin C
0.8(.02), Potassium 4.4(0.6), Sodium 140(7.9), and Urea 3.1(1.6).The
sensitivity of Cystatin C was 15.1% (95% CI= 8.4, 24) with specificity 99.3%
(95% CI=98- 99.7). Positive and negative predictive values were 70.0% (95% CI
45.7-88.1) and 91.2% (95% CI 98.11-92.94) respectively. Positive likelihood
ratio was 18.81 and negative likelihood ratio was 0.85. Cystatin C had
diagnostic accuracy of 90.7 and area under curve was 0.768.
Conclusions: Cystatin C exhibited
a high specificity and a high positive likelihood ratio in diagnosis of kidney
disease among HIV-positive patients.
E. Wekiya1, J. Nakiyingi2, J. Sanya2, J. Nakaweesi2, E. Mutebi3, D. Nakanjako3, Y. Karamagi2, E. Namitala2, G. Mujuzi2, B. Mukasa2, M. Matovu4
1Mildmay Uganda, Medical Services, Kampala, Uganda, 2Mildmay Uganda, Kampala, Uganda, 3Makerere University, College of Health Sciences, Kampala, Uganda, 4Makerere University College of Health Sciences, Clinical Epidemiology Unit, Kampala, Uganda