Occult Hepatitis B Infection: A Diagnosis to Have in Mind in Hemodialysis Patients.

Hepatitis B infection (HBV) is a global health problem, with several distinct manifestations and risk of progression to cirrhosis or hepatocellular carcinoma. Patients with chronic kidney disease on hemodialysis are particularly vulnerable to infection due to the risk of disease transmission related to vascular access use, passage of blood through the extracorporeal circuit, shared dialysis equipment, and occasional transfusion of blood products. The clinical consequences, lack of therapy capable of complete eradication of HBV, and the fact that it is the viral disease most frequently transmitted via the parenteral route in this population make its timely diagnosis important. Frequent screening of HBV infection is recommended, and serological tests are usually sufficient for diagnosis of the disease. However, occult HBV infection is a clinical entity that can be difficult to diagnose. It is defined as the absence of detectable surface antigen (AgHBs), with positive HBV deoxyribonucleic acid (DNA) but with viral serum measurement <200 IU/mL, but this value can be much smaller, making its detection harder. It can also be categorized as seronegative if the core (AcHBc) and surface antigen (AcHBs) antibodies are both negative, or seropositive if one or both are positive. The latter can be important in the diagnosis, as it suggests previous exposure to the virus and should lead to measurement of HBV DNA, which might not occur with seronegative occult HBV infection. These characteristics may make the proper diagnosis of this disease difficult, with clinical and public health implications. In this report, we present the case of an 85-year-old female patient with chronic kidney disease on hemodialysis. Routine screening of HBV AgHBs, AcHBc, and AcHBs had been previously negative. She was immunized with the HBV vaccine, and on the following screening, presented with negative AgHBs and AcHBc but positive AcHBs. After approximately two years of monitoring, an inconclusive measurement for AcHBc was detected. This prompted the assessment of HBV DNA, which was low but detectable (17 IU/mL). Reassessment, however, was negative (<10 IU/mL), with the other two measurements of 10 IU/mL (at the cutoff value, as defined by the laboratory) and later of 21 IU/mL. After these results, a diagnosis of occult HBV infection was considered. This report is an example of the difficulty in diagnosing this entity, requiring a high index of suspicion that leads to HBV DNA measurement. Low circulating levels of HBV DNA can still result in inconclusive results, but other markers, such as a positive AgHBc, might aid us in establishing this diagnosis. Its early detection is important for proper differential diagnosis of reactivation or acute infection and later monitoring and management of the risk of reactivation due to persisting infection.