Although both of them measure the ion activity of different ions in the specimen, the difference between ISE direct method and indirect method focus on the direct method is determined directly without dilution, while the indirect method is determined after pre-dilution. The former reflects the most realistic patient sample state and is therefore persuasive, whereas the direct method is susceptible to potential calibration biases (which the GE series has been able to avoid); However, the use of sample dilution increases the cost of a single test, and the dilution process is also prone to contamination, and the feedback is not the most real situation of the patient.