What is ISNA?
Returns TRUE if the value is the #N/A error. More specific than ISERROR for lookup failures.
Syntax
=ISNA(value)
Example
Formula: =ISNA(VLOOKUP(A1, Data, 2, FALSE))
Result: TRUE or FALSE
How It Works
Returns TRUE only for #N/A (not available) errors. Common with failed lookups. Use IFNA for simpler handling.