Are you asking why different analytes (like creatinine, or everything from liver enzymes to CRP to specific antibodies) have different reference ranges? Or are you asking about variation in testing results between different laboratories?
The answer to the former is because different analytes are present in different amounts in healthy people who were tested to establish those reference ranges.
The answer to the latter is that there is always some random noise inherent in biochemical tests, and small factors in different labs’ procedures may nudge it in a particular direction. Good lab practices and standardized testing materials can minimize that.
E: creatinine at 1.1 (assuming mg/dL) is just about on the high side of its usual reference range. Given some random noise in the measurement, you could think of that as “possibly normal, possibly slightly above normal”.
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