Serum free light chain analysis: persisting limitations with new kids on the block.

OBJECTIVES: Serum free light chain (sFLC) measurements have inherent analytical limitations impacting sFLC clinical interpretation. We evaluated analytical and diagnostic performance of three polyclonal sFLC assays on four analytical platforms. METHODS: sFLC concentration was measured using Diazyme FLC assays (Diazyme) on cobas c501/c503 analyzer (Roche); Freelite assays (The Binding Site) on Optilite analyzer (The Binding Site) and cobas c501 analyzer and Sebia FLC ELISA assays (Sebia) on AP22 ELITE analyzer (DAS). Imprecision, linearity, method comparison vs. Freelite/Optilite, antigen excess detection and reference value verification were assessed. Diagnostic performance was compared on 120 serum samples and on follow-up samples of five patients with κ and λ monoclonal gammopathy. RESULTS: Method comparison showed excellent correlation with Freelite/Optilite method for all assays. A large proportional negative bias was shown for both Sebia κ and λ ELISA and a significant positive proportional bias for λ in the low (<10 mg/L) Freelite/cobas c501 method. Clinically relevant underestimation of κ sFLC levels due to antigen excess was shown for 7% of each Diazyme/cobas application and for 11 and 32.1% of λ sFLC assay of respectively Diazyme/cobas and Sebia/AP22. sFLC reference values revealed application specific. Cohen's κ values were (very) good for κ sFLC but only moderate to good for λ sFLC. In 4/10 follow-up patients, significant differences in clinical interpretation between sFLC assays were noticed. CONCLUSIONS: Important analytical limitations remain for all sFLC applications. Differences in reference values and diagnostic performance hamper interchangeability of sFLC assays. Assay specific sFLC decision guidelines are warranted.

From Delta to Omicron SARS-CoV-2 variant: Switch to saliva sampling for higher detection rate.

Background: Real-time polymerase chain reaction (RT-PCR) testing on a nasopharyngeal swab is the current standard for SARS-CoV-2 virus detection. Since collection of this sample type is experienced uncomfortable by patients, saliva- and oropharyngeal swab collections should be considered as alternative specimens. Objectives: Evaluation of the relative performance of oropharyngeal swab, nasopharyngeal swab and saliva for the RT-PCR based SARS-CoV-2 Delta (B.1.617.2) and Omicron (B.1.1.529) variant detection. Study design: Nasopharyngeal swab, oropharyngeal swab and saliva were collected from 246 adult patients who presented for SARS-CoV-2 testing at the screening centre in Ypres (Belgium). RT-PCR SARS-CoV-2 detection was performed on all three sample types separately. Variant type was determined for each positive patient using whole genome sequencing or Allplex SARS-CoV-2 variants I and II Assay. Results and conclusions: Saliva is superior compared to nasopharyngeal swab for the detection of the Omicron variant. For the detection of the Delta variant, nasopharyngeal swab and saliva can be considered equivalent specimens. Oropharyngeal swab is the least sensitive sample type and shows little added value when collected in addition to a single nasopharyngeal swab.

Thrombin generation measured by two platforms in patients with a bleeding tendency.

BACKGROUND: Mild to moderate bleeding disorders are a diagnostic challenge. Many patients remain undiagnosed despite thorough and repeated laboratory testing. Thrombin generation (TG) is an overall assay measuring the functionality of the hemostatic system and may be a useful tool in diagnosing patients with bleeding tendency. OBJECTIVES: We examined the added value of TG in patients with mild bleeding tendency with and without diagnosis after classical laboratory testing. Further, we investigated the role of different expressions of results, between-method variation, and reference ranges. METHODS: TG of patients and controls was measured in parallel by two TG platforms (ST Genesia and calibrated automated thrombogram [CAT]). All TG parameters in patient and control groups were compared by statistical analysis (Mann-Whitney U tests) including visual representation with box-and-whisker plots. Results were expressed as normalized ratios (ST Genesia and CAT) or corrected values (ST Genesia). Reference intervals were calculated to which patient results were compared. We studied lot-to-lot reagent variability for both platforms. RESULTS: In 62.7% (ST Genesia) to 69.5% (CAT) of patients undiagnosed with a traditional laboratory work-up, abnormal TG parameters (lag time and endogenous thrombin potential expressed as normalized ratio and/or corrected value) were detected. In the group of previously diagnosed patients, abnormal parameters were found in 58.1% of patients for both TG assays. No relevant lot-to-lot reagent variability was observed. CONCLUSIONS: Adding TG helps with diagnosing patients with mild bleeding disorder. TG seems a promising tool in diagnosis of bleeding tendency, but further evaluation is necessary before application in diagnostic laboratory testing.