Introduction.
Globally, 170 million individuals are chronically infected with Hepatitis C virus (HCV). The hallmark of HCV infection is the progressive development of liver fibrosis, leading to liver cirrhosis and potentially hepatocellular carcinoma. The level of liver fibrosis predicts liver related complications and therefore the assessment of liver fibrosis is a cornerstone in the management of patients chronically infected with HCV. Each year 0.5 million people die of HCV-related diseases.

For the last fifty years, liver biopsy has been considered the gold standard for fibrosis and cirrhosis assessment, but recent reports indicate that biopsy does not fulfill the requirements of a surrogate marker; mainly because of its high complication and sampling error rate, high inter- and intra observer variability, cost and patient reluctance to undergo serial monitoring [1], [2]. In the last decade, several promising non-invasive alternatives have emerged. Liver stiffness measurement using FibroScan (Echosens, Paris, France) is a rapid method with high accuracy for the monitoring of HCV induced fibrosis and cirrhosis [1]. Also blood sample tests, such as the FibroTest (Biopredictive, Paris, France), have been shown to have a good correlation with advanced liver fibrosis.

There are limitations to the novel non-invasive tools. The FibroScan is expensive to acquire and the blood tests rely on accurate measurement using multiple assays. These tests are therefore only offered in a few, validated laboratories. As these promising novel modalities will most likely not reach the large majority of HCV infected patients in the developing world, simpler and cheaper alternatives are needed.

A series of reports have demonstrated that chemokine Interferon-γ Inducible protein 10 (IP-10, CXCL10) is a promising single marker correlate for liver fibrosis, and an IL-28b independent negative predictor of treatment outcome in HCV infected patients[3]–[7]. IP-10 is a key driver in both innate and antigen specific immune responses by directing Th1 cells to the site of inflammation [8], [9]. IP-10 is secreted by HCV infected hepatocytes into the blood and can therefore be seen as a direct proxy of ongoing inflammation in the liver [10], [11]. Recently, it was shown that in patients with chronic HCV infection the majority of plasma IP-10 exists in a 2 amino-acid truncated antagonist form, which inhibits the desired antiviral effects of IP-10 and could play an important role in pathology [12]. Compared to most of the key pro-inflammatory T cell cytokines (e.g. IFN-γ), IP-10 is expressed in 100 fold higher levels making it easy to measure also with simple technology [13].

Drying of plasma and blood on filter paper is a reliable method for conserving proteins. The method is state-of-art in national screening programs of neonates and it enables very simple sample acquisition (e.g. a finger or heel prick), and safe and cheap long distance transport using normal mail service [14]. Recent publications have demonstrated that dried blood spots (DBS) are a reliable alternative to serum specimens for detecting anti-HCV, quantifying HCV RNA and genotyping HCV [15]. We have recently developed an ELISA based assay for IP-10 detection in DBS and dried plasma spots (DPS) [16]. Using this assay we have demonstrated a very high correlation between DPS, DBS and plasma IP-10 levels in sample from healthy donors and patients with M.tuberculosis infection, and that this method renders comparable diagnostic accuracy as the current state-of-art diagnostic assay for infection with M.tuberculosis, the Quantiferon test (Aabye et al unpublished). It is unknown how the filter paper based method for IP-10 detection performs in samples from patients with chronic HCV infection. The aim of this study was to assess if the filter paper based method for IP-10 detection compares to IP-10 detected in plasma from HCV infected patients with either minimal or significant liver fibrosis.

Abstract.
The chemokine IP-10 (CXCL10) is a candidate marker for hepatitis C virus (HCV) fibrosis monitoring. The aim of this proof-of-concept study is to assess if IP-10 measurements from dried plasma spots (DPS) are accurate in HCV-infected patients with either minimal or significant fibrosis. We measured IP-10 levels in plasma and DPS of 21 HCV-infected patients with cirrhosis and 19 patients with no/little fibrosis (determined with FibroScan). Cirrhotic patients had significantly higher levels of IP-10 compared to patients with minimal fibrosis. DPS and plasma measurements of IP-10 are comparable and the correlation was excellent (r2 = 0.97, p<0.0001). The DPS based method for IP-10 detection performs well in HCV-infected patients with either minimal or significant fibrosis.