Pseudohyperkalemia in horses with rhabdomyolysis reported by an enzymatic chemistry analyzer.

The research article investigates why the VetScan VS2 analyzer, a device used for processing serum chemistry profiles, could potentially give falsely elevated readings of potassium concentrations (pseudohyperkalemia) in horses with a muscle-deteriorating condition known as rhabdomyolysis. This was assessed through testing methods involving 18 horses diagnosed with rhabdomyolysis, and incorporating different ion-specific analyzers for comparison. The outcome recommends using a different analyzer to assess serum potassium levels in such horses, as the VetScan VS2 methodology is shown to indeed cause pseudohyperkalemia.

Research Background and Objectives

• The purpose of the study was to explore instances of pseudohyperkalemia – false detections of high potassium levels – that was hypothesized to occur in horses diagnosed with rhabdomyolysis.
• The research aimed to achieve this by comparing potassium concentration results from the VetScan VS2 analyzer with those from different ion-specific analyzers, such as i-STAT Alinity Base Station, Catalyst, and Cobas c501.

Methods

• 18 horses diagnosed with rhabdomyolysis were included in the study. Degrees of rhabdomyolysis were determined by creatine kinase levels, with a CK level exceeding 1,000 U/L considered as rhabdomyolysis.
• For the first part of the study, 3 horses with CK levels above 5,800 U/L and a continuous VetScan-detected potassium concentration exceeding 8.5 mmol/L were reassessed using the other mentioned analyzers.
• In the second part, paired serum samples from 15 additional horses were analyzed by the VetScan VS2, and then by the Cobas c501 analyzer.
• Different statistical methods like Bland-Altman and Wilcoxon ranked tests were employed for comparison of potassium concentrations from the VetScan VS2 and other analyzers. The correlation of these readings with log10 CK activity was also studied through Pearson correlation.

Results

• The research revealed significant differences in potassium concentrations as detected by the VetScan VS2 and other ion-specific analyzers. VetScan VS2 showed misleadingly inflated potassium levels (6.7 ± 1.6 mmol/L) when compared to ion-specific analyzers (4.0 ± 1.1 mmol/L).
• Also, a strong positive correlation was established between potassium concentrations and log10 CK activity when using the VetScan VS2 analyzer, but not with the Cobas analyzer.

Conclusion

• The study concluded by advising against use of VetScan VS2 to measure serum potassium concentrations in horses with rhabdomyolysis – an alternative, more reliable analyzer should be employed.
• It was stipulated that the VetScan’s misleading results stemmed from its methodology which uses lactate dehydrogenase, a substance that increases in serum alongside rhabdomyolysis and in turn causes a false elevation in detected potassium concentrations.