Comparison of methods for sodium and potassium determination in llama urine

To compare results for sodium and potassium determination on llama urine, using flame emission spectrophotometry (flame photometry), atomic absorption spectrophotometry (AAS), indirect ion-selective electrode potentiometry (ISE), and direct ISE.

Llama urine samples encompassing a wide range of electrolyte concentrations were analyzed for sodium and potassium concentrations, using 4 analytical methods, and results were compared statistically to assess correlation, bias, and potential interferents.

10 healthy male llamas.

Urine specimens were obtained from llamas fitted with urine collection apparatus at defined intervals over a 24-hour period. Urine samples were centrifuged, and supernatants were frozen at -70 C until analysis. Analytical procedures were done, using standard laboratory protocols. Means, correlation coefficients, and bias were calculated, and differences were evaluated by ANOVA, with significance set at P < 0.05.

There was strong correlation and good agreement among sodium values obtained by flame photometry, AAS, and indirect ISE. Sodium values obtained by use of direct ISE correlated poorly with other methods; urine is not an acceptable specimen for this method. Only AAS and indirect ISE had good correlation (r > 0.9) for potassium values. Data did not suggest presence of a potassium chelator in llama urine; urine potassium values measured by indirect ISE were significantly higher (by 150 to 200 mmol/L) than those measured by other methods.

Urine electrolyte analysis in llamas resulted in less agreement between methods than is generally found for serum. Data collection for patient monitoring or research analysis should be restricted to a single method to avoid differences in results attributable to analytical variance.