Tonicity, osmolality, effective and ineffective Osmoles

Consider these questions that may arise in the assessment of patients with hyponatremia:

In patients with hyperglycemia, is correction of the serum sodium necessary?  Is the corrected serum sodium a valid indication of the risk for neurologic complications, or should one use the uncorrected sodium?

High blood alcohol levels may be associated with an elevated osmolality even in the presence of hyponatremia. Does this impact how we should interpret the serum sodium level? 

How does one interpret serum sodium in the face of extreme hypertriglyceridemia?

The answers to these types of questions depend on an understanding of the concepts of tonicity, osmolality, effective osmoles, and ineffective osmoles. These advanced concepts are covered in the JAMA Internal Medicine review linked here: 

Hyponatremia, Hyposmolality, and Hypotonicity:  Tables and Fables


Below is table 2 from the article which summarizes the key concepts.