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General product and laboratory information only; this page is not medical advice and gives no bench procedure.
Short answer
A supravital stain is a dye applied to living, unfixed cells so that structures such as the residual RNA in young red cells become visible. In haematology, new methylene blue and brilliant cresyl blue are the dyes used for the reticulocyte stain. In the US, the FDA product code GJH covers the reticulocyte stain, which falls under 21 CFR 864.1850.
Definition and scope
“Supravital” means the cells are still alive when they meet the dye, unlike a fixed smear stained with a routine Romanowsky-type method (see Diff-Quik stain and differential staining). The best-known use is counting reticulocytes, immature red cells, in peripheral blood. One manufacturer describes its brilliant cresyl blue as a “supravital haematology stain for counting the reticulocytes in peripheral blood smears” and as “certified as a supravital stain for reticulocytes” (Agar Scientific product page, checked 2026-10-30). For the wider field, see what is hematology.
How a reticulocyte stain is used in practice
A 2022 study in Diagnostics (Basel), “Impact of Staining Methods and Human Factors on Accuracy of Manual Reticulocyte Enumeration” (PMC9498021, checked 2026-10-30), shows the kind of work a manual method involves. It compared four manual approaches with an automated Sysmex XE-5000 analyser on 100 venous samples read by two technologists, using brilliant cresyl blue (BCB) or new methylene blue (NMB), each with or without Liu’s counterstain. The authors describe both dyes as targeting RNA residues in reticulocytes and giving a characteristic blue reticular pattern, and the slides were counted under oil immersion. Laboratories rely on their own validated procedures and the manufacturer’s instructions for use for the actual method.
New methylene blue vs brilliant cresyl blue
Both dyes are used for the same purpose, so the practical question is which agreed better with the analyser. In that study, the least bias came from BCB, then NMB. The mean bias figures reported were 8.77 for BCB and 23.29 for NMB. Adding Liu’s counterstain raised them to 38.8 (BCB) and 39.38 (NMB). Agreement between the two observers was high (intraclass correlation above 0.95), a figure the authors report for inter-observer consistency.
| Method in the study | Reported mean bias vs analyser |
|---|---|
| BCB alone | 8.77 |
| NMB alone | 23.29 |
| BCB with Liu’s counterstain | 38.8 |
| NMB with Liu’s counterstain | 39.38 |
Source: PMC9498021, checked 2026-10-30. This is one 100-sample comparison by two technologists, so treat it as evidence about that setup, not a ranking for every laboratory.
Where it matters for labs, clinics and supply decisions
Regulatory class
21 CFR 864.1850 (Dye and chemical solution stains) describes these products as “mixtures of synthetic or natural dyes or nondye chemicals in solutions” and classifies them as Class I (general controls). They are exempt from premarket notification (510(k)), subject to the limitations in 21 CFR 864.9, and exempt from the quality system regulation except for records and complaint files under 820.35 (eCFR, checked 2026-10-30). The tie to the reticulocyte stain comes from the FDA product classification (code GJH), not from the CFR text itself, which does not name reticulocytes.
What the product documents can tell you
| Item on the label or product page | What the source shows |
|---|---|
| Stated use | Agar Scientific states BCB is certified as a supravital stain for reticulocytes. |
| Hazard labelling | The same page labels the product Harmful; see GHS classification of chemicals for how such labels are assigned. |
| Chemical form | BCB exists in two forms, a 2-methyl (current) and an 8-methyl (historic) form, with the same application per the manufacturer. |
Common misunderstandings
- It is not a fixed-smear stain. Supravital staining acts on living cells; contrast it with H&E or acid-fast methods such as Ziehl-Neelsen, which are applied to fixed material.
- BCB is not only a blood stain. The manufacturer notes it is also used in oocyte selection, where low G6PD activity oocytes stay blue.
- Counterstaining does not automatically help. In the study above, Liu’s counterstain added bias for both dyes.
FAQ
What is a supravital stain?
A dye applied to living, unfixed cells to show structures that fixation would alter, most commonly the RNA in reticulocytes.
Are new methylene blue and brilliant cresyl blue the same?
They are different dyes used for the same reticulocyte-staining purpose. In the PMC9498021 comparison, BCB alone showed less bias than NMB alone against an automated analyser.
Is a reticulocyte stain regulated by the FDA?
Yes. Dye and chemical solution stains are Class I under 21 CFR 864.1850 and 510(k)-exempt, with record and complaint-file duties.
Sources
- 21 CFR 864.1850, Dye and chemical solution stains (eCFR, checked 2026-10-30)
- Impact of Staining Methods and Human Factors on Accuracy of Manual Reticulocyte Enumeration, Diagnostics 2022 (checked 2026-10-30)
- Agar Scientific, Brilliant Cresyl Blue (manufacturer page, checked 2026-10-30)
