NHS Number Validation

I’ve been working on NHS number validation recently so thought I’d share my code. Although there is guidance available on how to validate NHS numbers using modulus 11 check digit valiation, no one seems to have put up any code for it. It’s simple but hopefully it’ll be useful.

It will obviously not tell you whether a particular number has been assigned to a patient. It will only tell you if the number has a valid check digit. It is still a useful tool for checking large volumes of records for transcription errors and the like.

I’ve succesfully used it in three different languages: T-SQL, Excel VBA and R. In all three cases it is implemented as a user defined function which will return either 1 or 0 (1 = valid, 0 = invalid).

T-SQL

CREATE FUNCTION [dbo].[fnNHSvalidation] (@NHSnumber NVARCHAR(10))
RETURNS INTEGER
AS

BEGIN

/*Declare variables to hold values for calculation and output*/
DECLARE @ReturnValue INTEGER
DECLARE @Modulus INTEGER
DECLARE @UniformNumberCheck NVARCHAR(1)
DECLARE @NHSlength INTEGER

/*Find the length of the supplied NHS number*/
SET @NHSlength = LEN(@NHSnumber)

/*Declare variables to hold each digit of the NHS number, note that J is the check digit*/
DECLARE @A INTEGER
DECLARE @B INTEGER
DECLARE @C INTEGER
DECLARE @D INTEGER
DECLARE @E INTEGER
DECLARE @F INTEGER
DECLARE @G INTEGER
DECLARE @H INTEGER
DECLARE @I INTEGER
DECLARE @J INTEGER

/*Set variables to respective digits*/
SET @A = SubString(@NHSnumber,1,1)
SET @B = SubString(@NHSnumber,2,1)
SET @C = SubString(@NHSnumber,3,1)
SET @D = SubString(@NHSnumber,4,1)
SET @E = SubString(@NHSnumber,5,1)
SET @F = SubString(@NHSnumber,6,1)
SET @G = SubString(@NHSnumber,7,1)
SET @H = SubString(@NHSnumber,8,1)
SET @I = SubString(@NHSnumber,9,1)
SET @J = SubString(@NHSnumber,10,1)

/*Step 1: Ensure NHS number digits are not all equal (there is probably a FAR more elegant way of doing this)*/
IF ((@A = @B) AND (@B = @C) AND (@C = @D) AND (@D = @E) AND (@E = @F) AND (@F = @G) AND (@G = @H) AND (@H = @I) AND (@I = @J))
SET @UniformNumberCheck = 1
ELSE
SET @UniformNumberCheck = 0

/*Step 2: Calculate modulus 11*/
SET @Modulus = ((@A * 10.0)+(@B * 9.0)+(@C * 8.0)+ (@D * 7.0)+(@E * 6.0)+(@F * 5.0)+(@G * 4.0)+(@H * 3.0)+(@I * 2.0))
SET @Modulus = 11-(@Modulus % 11)

/*Step 3: Logical statement to establish if NHS number is valid based on results of previous steps*/
IF (@Modulus=@J AND @UniformNumberCheck 1 AND @NHSlength=10) OR (@Modulus = 11 AND @J = 0 AND @UniformNumberCheck 1 AND @NHSlength = 10)
SET @ReturnValue = 1
ELSE SET @ReturnValue = 0

/*Generate output: 1 indicates a valid NHS number, 0 indicates an invalid NHS number*/
RETURN @ReturnValue

END

GO

Excel VBA

Function NHSvalidation(NHSnumber)

Dim Modulus As Integer
Dim UniformNumberCheck As Integer
Dim NHSlength As Integer

NHSlength = Len(NHSnumber)

Dim A As Integer
Dim B As Integer
Dim C As Integer
Dim D As Integer
Dim E As Integer
Dim F As Integer
Dim G As Integer
Dim H As Integer
Dim I As Integer
Dim J As Integer

A = CInt(Mid(NHSnumber, 1, 1))
B = CInt(Mid(NHSnumber, 2, 1))
C = CInt(Mid(NHSnumber, 3, 1))
D = CInt(Mid(NHSnumber, 4, 1))
E = CInt(Mid(NHSnumber, 5, 1))
F = CInt(Mid(NHSnumber, 6, 1))
G = CInt(Mid(NHSnumber, 7, 1))
H = CInt(Mid(NHSnumber, 8, 1))
I = CInt(Mid(NHSnumber, 9, 1))
J = CInt(Mid(NHSnumber, 10, 1))

If ((A = B) And (B = C) And (C = D) And (D = E) And (E = F) And (F = G) And (G = H) And (H = I) And (I = J)) Then
UniformNumberCheck = 1
Else
UniformNumberCheck = 0
End If

Modulus = ((A * 10) + (B * 9) + (C * 8 ) + (D * 7) + (E * 6) + (F * 5) + (G * 4) + (H * 3) + (I * 2))
Modulus = (11 - (Modulus Mod 11))

If (Modulus = J And UniformNumberCheck <> 1 And NHSlength = 10) Or (Modulus = 11 And J = 0 And UniformNumberCheck <> 1 And NHSlength = 10) Then
NHSvalidation = 1
Else
NHSvalidation = 0
End If

End Function

R

NHSvalidation <- function(NHSnumber){

NHSlength<-length(NHSnumber)

A<-as.numeric(substr(NHSnumber,1,1))
B<-as.numeric(substr(NHSnumber,2,2))
C<-as.numeric(substr(NHSnumber,3,3))
D<-as.numeric(substr(NHSnumber,4,4))
E<-as.numeric(substr(NHSnumber,5,5))
F<-as.numeric(substr(NHSnumber,6,6))
G<-as.numeric(substr(NHSnumber,7,7))
H<-as.numeric(substr(NHSnumber,8,8))
I<-as.numeric(substr(NHSnumber,9,9))
J<-as.numeric(substr(NHSnumber,10,10))

if ((A==B)&(B==C)&(C==D)&(D==E)&(E==F)&(F==G)&(G==H)&(H==I)&(I==J))

{UniformNumberCheck<-1}

else

{UniformNumberCheck<-0}

Modulus<-((A*10)+(B*9)+(C*8)+(D*7)+(E*6)+(F*5)+(G*4)+(H*3)+(I*2))
Modulus<-(11-(Modulus%%11))

if (

((Modulus==J) & (UniformNumberCheck!=1) & (NHSlength==10))|((Modulus==11) & (J==0) & (UniformNumberCheck!=1) & (NHSlength==10)))
{ReturnValue<-1}
else
{ReturnValue<-0}

return(ReturnValue)
}