Five common errors in pharma serialization codes and how to catch them on the line

The code on a medicine pack is more than a barcode: it carries the product identity, serial number, expiration date and batch in a single symbol. If any of these four fields is wrong, the pack causes trouble in shipping, at the pharmacy or in the regulatory report — whether that is Türkiye's ITS or the EU's FMD system. The errors below are the ones we see most often in the field; all of them can be caught at the start of the line by reading every printed code and parsing it field by field.

1. A missing separator after the serial number

In a GS1 code the GTIN (01) and the expiration date (17) have a fixed length, while the serial number (21) and the batch (10) are variable-length. Unless a variable field comes last, it must be followed by a separator (FNC1, ASCII 29). Without it, the scanner reads the date and batch that follow as part of the serial number. The code is printed and read — but read wrongly.

Prevention: fix the field order in the printer template; the verification camera should parse the printed content field by field instead of only checking "read / not read".

2. A GTIN with a wrong check digit

The last digit of a GTIN is a check digit computed from the others. A GTIN typed into master data by hand, or converted incorrectly from 13 to 14 digits, is printed wrongly on every pack on the line. Because the error starts in the data, not in the symbol, the camera reports "read" while the code is invalid.

Prevention: software should validate the check digit when the GTIN is entered into master data and when a work order is opened.

3. Date format confusion

The expiration date uses YYMMDD: year, month, day. A date entered out of DD.MM.YY habit can turn into a valid but wrong date in the symbol. Day "00" means the last day of the month, which causes inconsistencies between systems that do not handle it explicitly.

Prevention: take the date automatically from the work order instead of having operators type it; read the printed date back and compare it with the work order.

4. Duplicate serial numbers

The same serial number printed on two packs usually happens when a line is restarted or two lines share the same number pool. A duplicate code causes problems in reporting and breaks the traceability of the product in the field.

Prevention: serial numbers should come from a central, collision-free generator; printed and rejected numbers should be recorded permanently and never reused.

5. Characters outside the character set

GS1 alphanumeric fields use a limited character set: accented letters and spaces are not part of it. An accented letter or a space in a batch number violates the GS1 rules; depending on the scanner and system, the code is rejected or misread.

Prevention: define the batch and serial number format as a rule in master data and check it when the work order is opened.

Quick check

You can check the content of a code taken from the line in your browser with our GS1 barcode decoder: it splits the fields, validates the check digit and the date, and checks that the four serialization fields are present. The lasting fix is to run these checks on the line itself, for every pack.