The LOINC code is a numeric code suffixed by a dash and Mod 10 check digit. This formula is also referred to a Luhn algorithm. The digit is used as an integrity check.

The algorithm for calculating a Mod 10 check digit is as follows. Note that this algorithm is slightly different for LOINC codes with a prefix (e.g, LP, LL, LA, LG).

Step 1

Using the number 12345, assign positions to the digits, from right to left.

Example:

1st = 5
2nd = 4
3rd = 3
4th = 2
5th = 1

Step 2

Take the odd digit positions counting from the right (1st, 3rd, 5th, etc.).

Example:

531

Step 3

Multiply by 2.

Example:

1062

Step 4

Take the even digit positions starting from the right (2nd, 4th, etc.).

Example:

42

Step 5

Prepend the results of Step 4 to the results of Step 3.

Example:

421062

Step 6

Add the digits of Step 5 together.

Example:

4 + 2 + 1 + 0 + 6 + 2 = 15

Step 7

Find the next highest multiple of 10.

Example:

20

Step 8

Subtract the value of Step 6 from the value of Step 7. Thus, 5 is the Mod 10 check digit for 12345.

Example:

20 - 15 = 5

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