UDI barcode verification: common problems

March 26, 2019

Medical Devices

By John Nachtrieb, Barcode-test LLC. Barcode quality trainer, consultant and testing service provider


Whether you are using 1D barcodes such as GS1-128 or 2D symbols such as Data Matrix codes for UDI compliance marking, UDI barcode verification is essential for assuring barcode quality. Here are some of the most common problems.



Whatever the print method, overprinting or gain is a frequent quality problem:

  • print head temperatures that are too high in thermal, thermal transfer
  • inkjet settings or ink viscosity that are incorrect for the substrate
  • impression settings too high in flexo printing

Visually compare the narrow black and white bars in a 1D barcode, or the dots or squares in a Datamatrix symbol: are they dimensionally equivalent? 



Metallic or metalized surfaces may not produce the high reflectance values one might logically expect—they often refract rather than reflect light. In these cases, reverse printing the barcode might be best. Patterned or textured surfaces can also be a problem.



Printing, graphics or product behind a barcode on a clear pouch can impair the scanability of an otherwise high quality barcode. Eliminate this by printing the barcode over a white patch.



1D barcodes such as GS1-128 require a minimum leading and training clear area. 2D symbols such as Data Matrix code require a full-surround quiet zone.

Printing a 1D barcode on a small label can be a problem, requiring the barcode to be very accurately and consistently positioned so that neither of the quiet zones is infringed.



Using a 1D barcode to encode a large amount of data can make it challenging to fit onto a label, as described above. Decreasing the X dimension makes it more difficult to print the barcode accurately and to scan it easily. A better solution s to replace the 1D symbol with a Data Matrix code.



This can be a problem as printing technology makes it possible to print the barcode on uneven surfaces. 1D barcodes are sensitive to distortion on one axis, but 2D symbols are sensitive on both axes. Avoid direct printing barcodes on bottles or other 3D objects, tapered or curved areas.



UDI barcode data structure is very specific. Data fields must be properly prefixed. Some fields are fixed length, and others are variable. This is an area where mistakes are often made. Using a well known, current version of label design software is good insurance against incorrectly structuring a UDI barcode.

Using an ISO compliant barcode verifier that tests for print quality and UDI data structure is an important best-practice.

Visit the Barcode-Test website for additional information.

An Error Occurred.