Codabar Barcodes: Blood Bank (ISBT 128 Legacy), Library & Air Waybill Guide

Invented in 1972 by Pitney Bowes, Codabar (internationally designated as NW-7 in Japan) holds a revered place in the history of automatic identification. Before modern high-density symbologies like Code 128 or QR codes existed, Codabar was entrusted with humanity's most sensitive data transactions: labeling whole blood transfusion bags, managing millions of university library books, and tracking FedEx overnight courier airbills.

Unlike modern retail barcodes that require high-precision laser imaging, Codabar was intentionally engineered to be readable even when printed by primitive 9-pin dot matrix impact ribbons, embossed credit card imprinters, or carbon copy forms.

In this definitive technical retrospective and engineering guide, we break down the 7-element binary mechanics, the functional role of the four distinct start/stop characters (A, B, C, D), and why modern medical systems have evolved from ABC Codabar to ISBT 128.

1. What Is Codabar (NW-7)?

Codabar is a discrete, self-checking linear barcode symbology capable of encoding 16 data characters along with 4 distinct start and stop delimiters.

In Japan, the standard is formally governed by JIS-X-0504 under the name NW-7, which directly describes its physical geometry: Narrow-Wide 7 elements.

2. Character Set & 7-Element Binary Structure

The standard Codabar data character set consists of exactly 16 characters:

• 10 Numeric Digits: 0 through 9
• 6 Punctuation Symbols: Hyphen (-), Dollar ($), Colon (:), Slash (/), Period (.), and Plus (+)

Every individual character is composed of 7 optical elements (4 dark bars and 3 white spaces) separated by a narrow inter-character space.

3. The Unique A, B, C, D Start/Stop Character Pairs

Unlike Code 39 (which uses a single universal asterisk * delimiter), Codabar features four unique start/stop characters: A, B, C, and D (in earlier literature called T, N, *, and E).

By varying which characters appear at the start and end of the string, system architects could encode document metadata without adding data digits:

• A ... B → Outbound customer package
• A ... C → Return receipt airbill
• B ... B → Whole blood red blood cell unit
• C ... D → Platelet concentrate unit

4. The Blood Bank Heritage: ABC Codabar to ISBT 128

In 1977, the American Blood Commission formalized ABC Codabar as the mandatory standard for labeling blood donor units across North America.

For over twenty-five years, every pouch of whole blood, plasma, and cryoprecipitate was identified by a 4-quadrant Codabar label containing:

1. Donor Registration Unit Number
2. ABO/Rh Blood Group
3. Product Code (e.g. Red Blood Cells, CPDA-1)
4. Expiration Date

5. Municipal & Academic Library Circulation Standards

While blood banks migrated to ISBT 128, hundreds of municipal and university libraries worldwide still utilize Codabar on the inside back covers of books and on patron library cards.

The standard library format consists of 14 numeric digits framed by start/stop character A and B:

• Digit 1: Patron vs Book Item Indicator (e.g., 2 = Patron Card, 3 = Book Volume)
• Digits 2–5: Institutional Library Identification Code
• Digits 6–13: Sequential Catalog or Patron Number
• Digit 14: Modulo-10 Check Digit

6. Overnight Courier Tracking (FedEx Airbill Legacy)

In the early days of overnight air courier logistics, Federal Express (FedEx) famously printed Codabar barcodes on multi-part carbon-copy Air Waybill forms.

Because couriers filled out paper waybills in the field using ballpoint pens, the bottom carbon slips were often smudged or misaligned. Codabar's massive optical tolerances ensured sorting hub wand scanners could read the tracking number even through wrinkled carbon paper.

7. Codabar vs Code 128: Why Modern Systems Migrated

While Codabar was revolutionary in 1972, it has been largely superseded by Code 128 for new enterprise deployments due to three structural limitations:

1. Extremely Low Data Density: Codabar takes up roughly twice as much label space as Code 128 to encode the same number of digits.
2. Limited Character Set: It cannot encode letters of the alphabet (only 0–9 and 6 symbols).
3. Lack of Native Checksum: Modern logistics networks demand high-security polynomial checksums to prevent misreads at 120-meter-per-minute conveyor speeds.

8. Check Digit Algorithms: Modulo-16 & Library Modulo-10

While Codabar standard specifications do not mandate a check digit, two mathematical checksum variations are common:

• Modulo-16 Checksum: Sum the numerical values of all data characters (0–15), divide by 16, and append the character matching the remainder ($R = \text{Sum} \pmod{16}$).
• Library Modulo-10 Checksum: Sum the odd-position digits multiplied by 2 and even-position digits multiplied by 1, subtracting the sum from the nearest multiple of 10.

9. Frequently Asked Questions