Expression Troubleshooting for App Formula

[mykrobinson]

I am trying to craft a formula for a column called "Previous UF Rate ml/min"

It's a decimal type, and what i am hoping to do is, in plain english best as i can,
look in the "aquadex aquapharesis" table and find the most recent timestamp, filtered by the currently viewed patient and where the "stop date" is blank, the return the "Current UF Rate" value from that row.

My expression is as follows

LOOKUP(MAXROW("Aquadex aquapharesis","Timestamp",
(AND(
[_patientIdentifier]=[_THISROW].[_patientIdentifier],
ISBLANK([Stop Date])
)),
"Aquadex aquapharesis","_aquadexID","Current UF Rate"
))

But i am getting an error that my MAXROW function should have at least two parameters. A table, a column, and an optional filter expression.

It looks to me like maxrow is looking at the Timestamp column in the Aquadex aquapharesis table the filter condition looks to be enclosed in the AND() function.

Where am i going wrong here?

[TeeSee1]

LOOKUP(
 MAXROW(
  "Aquadex aquapharesis",
  "Timestamp",
  (AND(
   [_patientIdentifier]=[_THISROW].[_patientIdentifier],
   ISBLANK([Stop Date])
   )
  ),
 ) <== This is missing
 "Aquadex aquapharesis",
 "_aquadexID",
 "Current UF Rate"
)
) <= this is not required

Seem like a simple case of illegal formatting.

Please re-examine your formula carefully.

The () around the AND makes is look more complex and would be better if removed.