Monitoring cystatin C levels a good way of detecting poor kidney function in patients with HIV

HIV infection is associated with poorer kidney function, if the health of the kidneys is measured by testing levels of cystatin C, American investigators report in the November 12^th edition of the Archives of Internal Medicine.

But the investigators found that when creatinine levels were monitored, kidney function was no different in HIV-positive patients and HIV-negative controls. They therefore suggest that measuring cystatin C could be a useful way of identifying HIV-infected patients at increased risk of kidney and cardiovascular disease.

Studies suggest that HIV-positive patients have an increased risk of kidney disease. This could be because HIV has a direct effect on the functioning of the kidneys, or because the illnesses that HIV infection can cause damage the kidneys. Furthermore, some of the drugs used to treat HIV infection are known to have an adverse effect on the kidneys.

It is therefore important than HIV-positive patients have their kidney function monitored at regular intervals.

Cystatin C is a measure of kidney function that is more sensitive in detecting moderate kidney disease than traditional creatinine-based tests. In particular, studies have shown cystatin C to be a superior measure of kidney function to monitoring creatinine in the context of chronic diseases, aging and conditions that can cause changes in body composition. All these can be important considerations for HIV-positive patients.

Investigators from a US study looking at body fat and metabolic changes in HIV-positive patients (the FRAM – Fat Redistribution and Metabolic Change in HIV Infection – cohort) therefore conducted a cross sectional study. They compared kidney function, measured by cystatin C and creatinine levels in 1008 HIV-positive patients and 208 HIV-negative controls.

Levels of cystatin C were elevated in HIV-positive patients compared to the HIV-negative controls (mean level, 0.92mg/l vs. 0.76mg/ml, p < 0.001). But creatinine levels were similar in the two groups of patients (0.87mg/dl vs. 0.85mg/dl).

Poor kidney and cardiovascular health is associated with cystatin C levels above 1.0mg/ml. The investigators found that HIV-positive patients were significantly more likely to have cystatin C levels above this threshold than the controls (OR, 9.8; 95% CI, 4.4 – 22.0, p < 0.001).

Factors associated with higher cystatin C levels in HIV-positive patients included high blood pressure, low HDL cholesterol, a lower CD4 cell count and coinfection with hepatitis C virus (all p < 0.001).

The investigators conclude, “HIV infection appears to be associated with substantially worse kidney function when measured by cystatin C level, whereas creatinine levels…were similar in HIV-infected individuals and controls.” They call for further studies to establish “the optimal role of cystatin C for detecting reduced kidney function in HIV or chronic infection[s].”