NHS numbers are the unique numbers allocated to registered users of the three public health services in England, Wales and the Isle of Man; the three health systems use a shared numbering scheme. It is the key to the implementation of the electronic health record, and is to be incorporated in all new software deployed within the National Health Service. The modern style of NHS number was generally introduced in 1996, although they were allocated to every new-born baby since July 1995, before becoming mandatory on 1 April 1997. It replaced the previous system founded on wartime identity card numbers, which in England and Wales used letters and digits ; Scotland used numbers based on households with individuals further identified within the household, and this meant that it was hard to validate a specific number. The numerical part of ID/NHS numbers allocated to people born after the Second World War in England and Wales matched the birth register entry number. Between 1969 and July 1995, the old-style NHS number was used on a baby's birth certificate as the reference number for the certificate. The current system uses a ten-digit number in '3 3 4' format with the final digit being a check digit. Examples given include 987 654 4321. The format includes an error-detecting checksum, which is the role of the final digit. Ignoring the check digit, each of the first nine digits is multiplied by 11 minus its position. Using the number 943 476 5919 as an example:
And so on until the ninth digit is multiplied by 2.
The result of this calculation is summed. In this example: 9*10+4*9+3*8+4*7+7*6+6*5+5*4+9*3+1*2 = 299.
The remainder when dividing this number by 11 is calculated, yielding a number in the range 0–10, which would be 2 in this case.
Finally, this number is subtracted from 11 to give the checksum in the range 1–11, in this case 9, which becomes the last digit of the NHS number.
A checksum of 11 is represented by 0 in the final NHS number. If the checksum is 10 then the number is not valid.
A person gets an NHS number at birth, or when they first make contact with the NHS by registering with a GP. It comes from a record being made on the Personal Demographics Service, a national patient database. Some people may have old NHS numbers following the format XXXX 999.
Number ranges and coordination with Scotland and Northern Ireland
Scotland's equivalent is called a CHI number; a similar system is also used in Northern Ireland with each one of the three using the same format but with non-overlapping number blocks, thus preventing the issue of the same number by more than one system. Currently issued numbers for England, Wales and the Isle of Man are from 400 000 000 to 499 999 999 and 600 000 000 to 708 800 001. Current numbers in England also include 3xx xxx xxxx and 72x xxx xxxx. Unavailable number ranges include 320 000 001 to 399 999 999 and 010 101 0000 to 311 299 9999.
