Researchers at Rutgers Robert Wood Johnson Medical School in New Brunswick, New Jersey, report that phosphate-buffered saline (PBS) is a “dependable transport medium for use with clinical samples” in detecting SARS-CoV-2 (J Mol Diagn 2020; doi.org/10.1016/j.jmoldx.2020.04.209). In comparing quantitative polymerase chain reaction (qPCR) results on 20 samples from two subjects, the investigators found a “strong correlation” between cycle threshold (Ct) values in samples transported in PBS or viral transport media (VTM), whether processed immediately or stored at room temperature and processed at intervals of up to 18 hours.
In light of continuing shortages of VTM during the COVID-19 pandemic, the investigators posited that PBS would be a viable transport medium and alternative to VTM for clinical qPCR testing. The Food and Drug Administration has authorized laboratories to consider testing alternative transport media for use with SARS-CoV-2 samples.
The investigators tested PBS- and VTM-transported samples in three experimental procedures using discarded respiratory secretions from 16 confirmed COVID-19 patients. In the first procedure, they collected eight samples from two patients at the same time, transported them in either PBS or VTM, and processed two samples from each patient immediately and after 2 hours at room temperature. The second procedure involved 20 samples each from two subjects, kept at room temperature and processed at 0, 2, 4, or 6 hours or overnight. The final procedure involved 24 samples from 12 patients, transported in either PBS or VTM and processed immediately.
The researchers compared Ct values for the SARS-CoV-2 nucleocapsid (N), open reading frame 1ab (ORF1ab), and spike protein (S) genes and used bacteriophage MS2 spiked into the samples as a positive control. Correlations between VTM- and PBS-transported samples were 0.93, 0.83, and 0.91 for the N, ORF1ab, and S genes, respectively. All were statistically significant, with P values <0.05.
This comparison involved samples from tracheal secretions of mechanically ventilated intensive care patients, so the researchers cautioned that their results might not extend to nasopharyngeal swabs, oropharyngeal swabs, or saliva samples.
Citing Lack of Evidence, Researchers Recommend Abandoning Use of Ammonia Levels in Managing Hepatic Encephalopathy
A study of 1,202 patients admitted for management of their hepatic encephalopathy (HE), a reversible neuropsychiatric complication of chronic liver disease, concluded that “there is no evidence that ammonia levels are important” in this clinical context (Am J Gastroenterol 2020;115:723-8). These results suggest that routine testing of ammonia levels either as an initial diagnostic for HE or to guide therapy “should be abandoned.”
An accompanying editorial concurred, noting that “there is a huge chasm between clinical practice and the evidence-based role for ammonia levels” (Am J Gastroenterol 2020;115:685-6). The investigators’ findings “so deeply devalue the clinical utility of ammonia that its widespread use now represents a clear unmet need for testing stewardship,” added the editorialists.
The researchers evaluated ammonia testing in HE patients admitted over a 10-year period to a single tertiary referral center. In all, 46% of patients had ammonia levels analyzed; 60% of those tested had abnormal results >72 µmol/L. The study’s primary end point, total oral lactulose given in the first 48 hours of HE admission, was not statistically significant between patients who had ammonia testing and those who didn’t (167 mL versus 171 mL). Further, average lactulose levels were the same in patients with elevated ammonia levels and in those without.
In a propensity matched study cohort of 296 patients who had ammonia levels drawn and 296 who didn’t, the researchers found one statistically significant difference between the groups: 21% of patients who did not have levels drawn versus 11.5% of those who did had HE secondary to dehydration (P = 0.0013). All other secondary end points, including time to resolution of HE, overall length of stay, admission to intensive care, and mortality, were not statistically significant.
C-peptide Levels Start Dropping 6 Months Before Diabetes Diagnosis; Continue at Same Decline for About 6 Months
C-peptide levels in individuals at risk for type 1 diabetes do not change significantly until about 6 months before these patients are diagnosed with the disease, and they continue to decline at about the same rate for 6 months after clinical diagnosis (Diabetes Care 2010; doi.org/10.2337/dc19-2288). After being diagnosed with type 1 diabetes, patients’ C-peptide response to oral glucose tolerance testing (OGTT) and mixed-meal tolerance testing (MMTT) is not significantly different. These findings suggest that to preserve patients’ beta-cell function, disease-modifying therapies should start at or before the time their C-peptide levels decline.
Researchers conducted a longitudinal analysis of 80 individuals at risk for type 1 diabetes who participated in the Pathway to Prevention Protocol of the Type 1 Diabetes TrialNet, a network of clinical trials designed to intervene in the type 1 diabetes disease process at any stage of disease, with the aim of preserving beta-cell function. The study involved screening for autoantibodies in relatives of individuals with type 1 diabetes, and closely monitoring those who developed autoantibodies until they progressed to type 1 diabetes. The study also followed a cohort after they were diagnosed to assess C-peptide response to OGTT and MMTT.
The subjects’ median age was 14 years, and they underwent a median of nine prediagnosis and two post-diagnosis OGTTs. The change in participants’ C-peptide levels was about 0 until approximately 6 months before their diagnosis, after which the change continued at the same negative rate. Participants’ mean fasting and 2-hr glucose levels also started to increase 6 months before they were diagnosed. The researchers found “no real differences” in participants’ C-peptide response to OGTT versus MMTT.