Image: The N Latex Cystatin C Assay for the detection of decline in renal function (Photo courtesy of Siemens Healthcare).
Beta Trace Protein (BTP) is a promising marker of glomerular filtration rate (GFR) as it was reported to be increased in the serum of patients with renal disease. Some evidence suggests that it is more sensitive than creatinine (Cr) at detecting early changes in GFR.
Unlike Cr, very little is known about the origin and metabolism of BTP. BTP is a heterogeneous glycoprotein with multiple isoforms and is present in various fluid compartments including blood, urine and cerebral spinal fluid (CSF). The impact of hepatic dysfunction on serum BTP concentrations has recently been investigated.
Scientists at Queen’s University (Kingston, ON, Canada) and their colleagues conducted a case-control study between June to October 2014 of 99 cirrhotic subjects and matched controls. The diagnosis of cirrhosis was confirmed by the hepatologists according to standard clinical criteria including non-invasive testing estimating F4 fibrosis in an individual with known chronic liver disease. Basic demographic, clinical and laboratory data were collected including diabetes status, etiology of cirrhosis, presence of ascites or encephalopathy, INR, albumin and bilirubin.
The team measured Cystatin C (cysC), BTP using nephelometry assays and Cr using a Vitros Chemistry enzymatic assay. The BTP/cysC ratio was calculated for each subject. The BTP/cysC ratio was chosen in lieu of the BTP/Cr ratio due to the well-recognized inaccuracy of serum creatinine as a marker of GFR in the setting of hepatic dysfunction.
The investigators found there were no differences in BTP/cysC ratios between cases and controls for the entire cohort. However there were significant differences between cases (1.09) and controls (0.73) for the BTP/Cr ratios. The BTP/Cr ratio was higher in those with more advanced cirrhosis as compared to those with less severe cirrhosis (1.20 versus 1.03). There were no differences in BTP/cysC ratios between those with less severe and more advanced cirrhosis.
The authors concluded that their study suggests that hepatic dysfunction does not influence serum BTP levels and argues against a significant role for the liver in BTP metabolism. It is well recognized that a number of factors (muscle mass, diet, hepatic function) influence serum Cr independently of GFR and these contribute significantly to the difficulties in accurately assessing GFR using Cr. The study was published on April 13, 2018, in the journal BMC Nephrology.