Is GFR and proteinuria measured in chronic hepatitis
Are the usual measurements of the glomerular filtration rate (GFR) and proteinuria applicable to patients with chronic hepatitis?
We know that the serum creatinine concentration results from the metabolism of creatine, which is a nitrogenous organic acid stored in muscles, which functions as an energy-providing catalyst.
There are two sources of creatine: endogenous liver production and exogenous oral ingestion.
About half the creatine comes from each source, which is extremely important when it comes to evaluating kidney function in patients with chronic hepatitis.
Most patients who are chronic carriers of either hepatitis B or C have significant inflammatory injury to the liver and may even have various stages of cirrhosis.
Creatine production in the liver will be significantly reduced, and this will lead to a lower serum creatinine. In the presence of cirrhosis, the synthesis of creatine can be reduced by more than 50%, and the oral intake of creatine will also be reduced as a result of malnutrition in these patients.
The typical serum creatinine is usually 0.5 to 0.6 mg/dL in patients with cirrhosis, which is well below the normal for the general population (1.2 mg/dL for women and 1.5 mg/dL for men). Patients with liver disease of any cause, not just HCV or HBV, can have significant loss of GFR with a serum creatinine level within “the normal range” for the general population.
For this reason, all physicians managing patients with chronic hepatitis should be cautious in interpreting kidney function using serum creatinine and should consider monitoring kidney function with either a 24-hour creatinine clearance or an estimated GFR (eGFR). The eGFR is calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD EPI) formula, and is always included on all automated reports that have a serum creatinine.
The use of cystatin C to measure the GFR in place of the serum creatinine may be of value, especially in patients with cirrhosis, since it is not affected by muscle mass, bilirubin levels, gender, or age. However, cystatin C is affected by albumin levels and by an inflammatory state, both of which are present in cirrhotic patients. While creatinine-based formulas have overestimated GFR in cirrhotic patients, cystatin-C-based formulas have consistently underestimated the GFRs. Studies have introduced a modified CKD-EPI formula that incorporates both the serum creatinine and cystatin C levels together, and this has shown to be superior in estimating the GFR compared to either creatinine-based or cystatin-C-based formulas alone.
In addition, all patients who are chronic hepatitis carriers should be screened for proteinuria. A random urine protein/creatinine ratio or a 24-hour urine protein collection is an equally valid way to quantify the degree of proteinuria. In patients with severe jaundice, the colorimetric dipstick may give false readings for protein because of the bilirubin pigment in the urine, so every positive urine dipstick test for protein should be confirmed with a quantitative measurement.
