Prevalence of pseudonatremia in a clinical laboratory - role of the water content.

BACKGROUND: Sodium concentration is a frequently used marker to discriminate between differential diagnoses or for clinical follow-up. Pseudonatremia, as a result of indirect ion-selective electrode (ISE) measurements in automated chemistry analyzers, can lead to incorrect diagnosis and treatment. We investigated whether the estimated water content, based on total protein and lipid concentrations, can be used to reduce diagnoses of pseudonatremia. METHODS: Indirect and direct ISE measurements of sodium were compared in blood samples from intensive care unit (ICU) (n = 98) and random non-ICU patients (n = 100). Differences between direct measurements using whole blood and lithium-heparin plasma were also determined. Water content, estimated by a linear combination of total protein and lipid concentrations, was used to correct indirectly measured sodium concentrations. The prevalence of pseudonatremia was evaluated in the ICU patient group. RESULTS: An absolute difference of 3 mmol/L was observed between direct measurements using lithium-heparin plasma and whole blood, with higher concentrations in plasma. Additionally, we observed that differences between indirect and direct measurements displayed a linear relationship with the estimated water content. The prevalence of pseudohypernatremia after indirect measurements (32%) was reduced when measurements were corrected for water content (19%). CONCLUSIONS: In critically ill patients, sodium concentrations should be preferably measured by direct measurements. Whole blood is the preferred material for these measurements. For routine sodium analyses in other patients, correction using the estimated water content appears promising in reducing the prevalence of pseudohypernatremia by indirect measurements.

Late Tuberculosis Reactivation After Severe Covid-19.

Background: Although there is no specific therapy for COVID-19, it is recommended that patients with severe SARS-CoV-2 infection are treated with corticosteroids and anti-IL-6 receptor monoclonal antibodies. Both COVID-19 itself and the treatment modalities mentioned above have suppressive effects on the immune system which may lead to an increased susceptibility to other infections. In patients with latent tuberculosis (TB) reactivation of TB infection after recovery from severe COVID-19 has been described. Most of these cases have occurred in parts of the world where tuberculosis is endemic. Case description: The patient is a female in her 70s who was born and raised in Southeast Asia and has lived in the Netherlands for more than 30 years. She was treated for a severe COVID-19 requiring mechanical ventilation for several weeks and pharmaceutical treatment with corticosteroids and anti-IL-6 receptor monoclonal antibodies (Sarilumab). She recovered well. Two years later she was readmitted with symptoms of a serious pulmonary infection and meningitis. Her condition deteriorated in a short time. An active TB infection was diagnosed. Despite adequate antibiotic treatment and supportive therapy her condition worsened and four days after admission to the ICU she deceased. Discussion: Reactivation of latent TB after recovery from a severe COVID-19 has been described several times and may occur several months after the SARS-CoV-2 infection. In this case the reactivation presented two years after COVID-19. This case illustrates that long-term follow-up of patients with latent TB that recover from a severe COVID-19 may be indicated. LEARNING POINTS: Reactivation of latent tuberculosis infection in patients treated for a severe COVID-19 may occur even two years after recovery from SARS-CoV-2 infection.Most cases of reactivation of tuberculosis after COVID-19 are described in regions where tuberculosis is endemic. However, it may also occur in countries with a relatively low prevalence of tuberculosis infection. The exact incidence of tuberculosis reactivation after COVID-19 is unknown and probably underestimated.A long-term follow-up of patients after severe COVID-19 treated with corticosteroids and/or anti-IL-6 receptor monoclonal antibodies with a history of tuberculosis or patients migrated from countries where tuberculosis is endemic seems to be important.