10% Neutral Buffered Formalin: Fixation Basics for Histology
What 10% NBF is, how much to use, how long to fix, and common fixation errors.
Short answer
10% neutral buffered formalin (NBF) is roughly 4% formaldehyde in a phosphate buffer at neutral pH, and it is the standard routine fixative in histopathology. Use about 10–20 times the tissue volume, keep specimens thin, and allow enough time; formalin penetrates slowly (on the order of 1 mm per hour) and cross-links more slowly still.
Why “10%” if it’s 4% formaldehyde?
“10% formalin” means a 1:10 dilution of concentrated formalin, which is about 37–40% formaldehyde. The working solution is therefore about 4% formaldehyde. Buffering to neutral pH helps prevent acid formalin pigment.
How much fixative should I use?
A fixative-to-tissue volume ratio of at least 10:1, and ideally 15–20:1, is the common recommendation. Too little fixative is one of the most frequent causes of poor fixation.
How long should tissue fix?
| Factor | Guidance |
|---|---|
| Penetration | Roughly 1 mm per hour; thick specimens fix from the outside in |
| Specimen thickness | Gross thin slices (about 3–5 mm) for even fixation |
| Breast specimens | ASCO/CAP guidelines specify 6–72 hours in NBF for ER/PR and HER2 testing |
| Time to fixative | Minimize cold ischemia time; place tissue in fixative promptly |
Common fixation mistakes
- Under-filled containers (ratio well below 10:1)
- Specimens too thick to fix through
- Processing before fixation is complete
- Unbuffered or depleted formalin
We fill NBF and specialty fixatives in bulk and prefilled formats. See stains, fixatives & decal.
Questions about this topic
What is the ratio of formalin to tissue?
At least 10:1 fixative to tissue by volume, with 15–20:1 often recommended.
How fast does formalin penetrate tissue?
On the order of 1 mm per hour, which is why specimens should be sliced thin for even fixation.
Do you supply prefilled formalin containers?
RightPath Medical Diagnostics fills neutral buffered formalin in bulk and prefilled formats. Contact us with the container size and volume you need.
Need this reagent filled?
RightPath Medical Diagnostics has blended and filled histology reagents since 2013, under our label or yours.