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Laboratory diagnosis of disorders in sodium or potassium homeostasis is affected by various factors among these the diagnostic method applied in the laboratory and the pre-analytical process. The sodium and potassium contents in plasma or serum can be determined by direct ISE “which requires no dilution step” and by indirect ISE or flame photometry, the latter techniques requiring a dilution step which influences the results.
A total of 26 blood samples collected from German Holstein cattle with laboratory values within the reference range were included for the agreement analysis between ISE (EML™ 105) and FAES (AAS, SOLAAR M6). The study using Bland and Altman statistical method demonstrated a considerable agreement in the measurement of sodium and potassium by the two analyzers which fulfill the requirements of the IFCC and CLSI. The mean difference between the two analyzers was -2.9±2.6 and -0.04±0.11 for sodium and potassium, respectively.
Total protein levels below the reference range tended to cause a pseudohyper- effect for potassium and sodium when FAES was applied whereas high total protein levels resulted in a pseudohypo- effect but the effect was more prominent for sodium. In addition, globulins were more likely shown to cause a pseudohypo- and pseudohyper- effect than albumin.
The effect of storage time and temperature on potassium and sodium ion concentrations was studied on whole blood samples from cattle stored at room temperature (22oC) and at 4oC with time interval up to 72 hours. Potassium ion concentrations showed a significant increase in samples stored at room temperature (22oC) (4.88±0.11 mmol/l) and at 4oC (5.82±0.23 mmol/l) at 24 hours and 72 hours following sampling, respectively, compared to the initial measurements (3.84±0.11 mmol/l). Sodium ion concentrations in samples kept at 22oC decreased significantly at 48 hours (139.6±0.42 mmol/l) while those kept at 4oC showed no significant differences up to 72 hours compared to the initial measurements (141.68±0.49 mmol/l). The sodium-potassium pump is implicated in increasing potassium and decreasing sodium concentrations stored at both storage temperatures.
Low temperature is important to conserve viable samples stored, the importance of performing the blood analysis as soon as possible or centrifugation of blood samples must not be excluded.
The effect of in vitro hemolysis on potassium concentrations was investigated in twenty bovine blood samples. The potassium values become falsely elevated in hemolyzed samples where, the concentration of potassium in non-hemolyzed and hemolyzed samples has a mean value of 4.99±1.14 mmol/l and 5.24±1.18 mmol/l, respectively. The plasma hemoglobin content in hemolyzed specimens was 82.77±68.1 mmol/l. A reliable correction factor to correct for falsely elevated potassium should be suitable in hemolyzed samples which are irretrievable. Where a high significant positive linear relationship between the change in potassium values and FPHgb from the non-hemolyzed to hemolyzed specimens existed; which offers a useful correction factor for potassium of 0.0025 (at 95% confidence interval, 0.0018 to 0.0031) x FPHgb in mg/dl.
Muscle tissue is considered of greater value as indicator for body potassium status as plasma samples or hemolysates. Blood and muscle biopsy samples from 13 German Holstein cattle were collected for determining the relationship between plasma and muscle potassium contents. The potassium concentrations in both plasma and muscle biopsy samples were 4.01±0.72 mmol/l and 89.59±11.87 mmol/kg wet weight, respectively. A very weak correlation between the potassium and sodium concentrations in plasma and those in muscle samples was observed. In addition, the pH-values was correlated to plasma potassium concentration but not correlated to muscle potassium content. The observed results indicate that the correlation between pH-values and plasma potassium concentration was independent from the changes in muscle potassium content in the same animal. For this, the evaluation of total body potassium content cannot be based on potassium concentrations in blood samples, due to fact that most of the body potassium is located inside the cell.