Validating NPI (National Provider Identifier) numbers in SQL

January 16, 2012 · 2 min read

If you work with any kind of healthcare data, then odds are you’ll deal with NPI (National Provider Identifier) numbers. The NPI is a 10-digit number consisting of 9 digits (with the first digit being a 1 or a 2) followed by a check digit. The check digit uses the Luhn algorithm, which is calculated like this: 

  1. Double the value of alternate digits beginning with the rightmost digit.
  2. Add the individual digits of the products resulting from step 1 to the unaffected digits from the original number.
  3. Subtract the total obtained in step 2 from the next higher number ending in zero.  This is the check digit.  If the total obtained in step 2 is a number ending in zero, the check digit is zero.

So for example:

Let's say the 9-digit part of the NPI is 123456789. NPI without check digit: 1     2     3     4     5     6     7     8     9 Step 1: Double the value of alternate digits, beginning with the rightmost digit. 2            6          10          14          18 Step 2:  Add constant 24, plus the individual digits of products of doubling, plus unaffected digits. 24 + 2 + 2 + 6 + 4 + 1 + 0 + 6 + 1 + 4 + 8 + 1 + 8 = 67 Step 3:  Subtract from next higher number ending in zero. 70 – 67 = 3 Check digit = 3 NPI with check digit = 1234567893 

We needed a way to check our SQL database for valid NPI numbers, so this SQL does the trick:

CREATE FUNCTION  [dbo].\IsValidNPI)  RETURNS int AS

-- Returns 1 for valid or missing NPI -- Returns 0 for invalid NPI

-- SELECT [dbo].\IsValidNPI
-- SELECT [dbo].\IsValidNPI\

BEGIN    Declare @Result int, @Len int, @Index int, @Total int, @TmpStr varchar(2), @TmpInt int    Set @Result = 0    Set @Total = 0    Set @NPI = IsNull(@NPI,'')    Set @Len = Len(@NPI)

   If @Len = 0       Set @Result = 1    Else    Begin       If @Len <> 10 or IsNumeric(@NPI) = 0 or @NPI like '%.%' or (@NPI not like '1%' and @NPI not like '2%')          Set @Result = 0       Else       Begin          Set @Index = @Len

         While @Index > 1          Begin             Set @TmpStr = Substring(@NPI, @Index, 1)             Set @Total = @Total + Cast(@TmpStr as int)

            Set @TmpStr = SubString(@NPI, @Index-1, 1)             Set @TmpInt = Cast(@TmpStr as int) * 2             If @TmpInt < 10                Set @Total = @Total + @TmpInt             Else             Begin                Set @TmpStr = Cast(@TmpInt as varchar(2))                Set @Total = @Total + Cast(Substring(@TmpStr,2,1) as int)                Set @Total = @Total + Cast(Substring(@TmpStr,1,1) as int)             End             Set @Index = @Index - 2          End

         If @Len % 2 = 1             Set @Total = @Total + Cast(Substring(@NPI,1,1) as int)          If @Len = 10             Set @Total = @Total + 24

         If @Total % 10 = 0             Set @Result = 1          Else             Set @Result = 0       End    End    Return(@Result) END

This article is part of the GWB Archives. Original Author: Bill Osuch

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