Bluestar and Hemastix

Standard luminol formulations contain sodium luminol or luminol dissolved in an alkaline solution with hydrogen peroxide added at the time of use, or pre-mixed in a two-component spray. The alkaline conditions needed for the reaction (pH 11-13) and the oxidative hydrogen peroxide are both individually capable of degrading DNA. Traditional formulations were optimised for visibility of the glow, not for what happened to the biological material afterward.

Bluestar Forensic was developed in France and introduced to wider use in the early 2000s. Its formulation uses a milder buffer, a lower working concentration of luminol, and a controlled peroxide concentration to produce a glow that is comparable in sensitivity to conventional luminol while reducing the cumulative chemical insult to DNA. Independent studies published in peer-reviewed journals generally support the claim of reduced DNA degradation, with Bluestar-treated stains showing higher rates of full STR profile recovery than the same stains treated with conventional formulations.

The detection sensitivity of Bluestar is broadly equivalent to standard luminol in practice. Manufacturer data and independent studies cite detection of blood at dilutions of 1:10,000 to 1:10,000,000 under favourable conditions, matching conventional luminol. The practical detection threshold on scene substrates is similar. The glow from Bluestar is reportedly slightly more persistent than some conventional formulations (lasting up to 2 minutes on a strong stain), which allows more latitude for photography in the field.

The practical decision follows directly from scene priorities. When the primary goal is mapping a large area quickly and DNA recovery is secondary (or the scene is so degraded that profiles are unlikely regardless), conventional luminol or Bluestar are both appropriate choices. When DNA is the primary evidential target and the area is manageable, fluorescein is preferred. When cost and logistics favour a simple prepared reagent, conventional luminol remains viable, provided the laboratory's validation data supports its DNA performance.

Hemastix was developed for clinical urinalysis, where it detects haematuria by the same peroxidase reaction now applied forensically. Urine is dipped or the strip is touched to a moist surface; the peroxidase-reactive pad changes colour from orange to blue-green in the presence of haemoglobin. The reaction uses a chromogenic indicator embedded in the pad, typically a tetramethylbenzidine (TMB) derivative, activated by haemoglobin's peroxidase activity in the presence of an organic peroxide impregnated in the pad itself. No separately added hydrogen peroxide is needed; the peroxide is pre-loaded.

In forensic use, the strip is applied to a cotton swab moistened with the suspected stain, or a small piece of the stain is dissolved in water and the strip is dipped. Results are read within 60 seconds: the pad colour is compared to the reference chart on the tube. A blue-green colour of any shade is positive; the intensity loosely correlates with haemoglobin concentration but should not be used for quantification.

1. Prepare the sample
   Moisten a cotton swab with distilled water and gently contact the stained area. Alternatively, place a small cutting of the stain in a few drops of water and agitate to dissolve.
2. Apply to Hemastix pad
   Touch the moist swab or dip the strip into the extract. Ensure the reagent pad makes firm contact with the sample. Read the result at 60 seconds; do not read late as prolonged contact can produce false-positives.
3. Read against reference chart
   The pad is read against the colour chart on the Hemastix tube. Any blue-green colour is a positive result. Record the intensity (trace, 1+, 2+, 3+) but do not use this as a quantitative measure.
4. Run controls
   A positive control (dilute blood standard or a previously positive known stain) and a substrate control (unstained area of the same material) are run alongside the sample.

Hemastix is more sensitive than the eye but less sensitive than the Kastle-Meyer test under controlled conditions. Most published studies put its detection limit at blood dilutions around 1:10,000 to 1:30,000, adequate for visible stains but potentially missing very dilute or aged material that a Kastle-Meyer test would catch. The strips also degrade with exposure to air and temperature: an open tube left at room temperature for weeks will give erratic results. Each strip should be from a sealed tube within the manufacturer's expiry date.

The false-positive profile is identical to the Kastle-Meyer test for the simple reason that Hemastix uses the same underlying chemistry: a TMB chromogen activated by haem-catalysed peroxide decomposition. Plant peroxidases, rust, bleach residues, and other oxidants will all produce a positive colour change. A substrate control (moistened swab from an unstained area of the same material) is mandatory.

Bluestar and Hemastix serve different points in the forensic workflow. Bluestar is a scene tool: it is sprayed across a room, a vehicle, or an outdoor area to locate latent bloodstains that are not visible to the naked eye. Its chemiluminescence illuminates the distribution of blood deposits from a distance, guiding collection decisions. It requires darkness, a camera, and an examiner trained to distinguish blood luminescence from bleach interference.

Hemastix is a point-of-contact tool. An examiner at the scene, or a laboratory technician at the bench, uses it to make a quick decision about a specific swab or extract. It does not map distributions; it tests a discrete sample. Its main advantages are convenience, the absence of mixing or preparation steps, and a negligible DNA impact (the strip touches only the swab, not the original stain).

• Bluestar: large-area search, cleaned scenes, vehicle interiors, outdoor scenes with limited ambient light, post-cleaning pattern reconstruction.
• Hemastix: rapid triage of individual swabs or cuttings, initial screen in the laboratory before committing to full processing, point-of-care decisions at the scene for discrete stains, quick verification that a known reference stain is still viable.
• Neither tool identifies human blood. Follow-up with HemaTrace or Hexagon OBTI (immunochromatographic strips specific for human haemoglobin) is required before reporting a stain as human blood.

In a well-resourced laboratory workflow, Bluestar may be used for scene searching, Hemastix for initial bench screening of swabs, the Kastle-Meyer test for the formal presumptive result with controls, and then HemaTrace for species confirmation, before DNA extraction proceeds. The tools are layered, not interchangeable.

The presumptive tests described across this module, Kastle-Meyer, LMG, luminol, Bluestar, and Hemastix, all feed into the same documentary record. A positive Bluestar glow must be photographed and described in notes. A positive Hemastix result must be recorded with the strip lot number, the expiry date, the positive and negative controls, and the result intensity.

The reason documentation is so thorough is that any of these results can become the subject of expert evidence at trial. A defence challenge may focus on whether the correct controls were run, whether the reagent was within date, whether the substrate control was positive, or whether the examiner was trained and competent. Thorough records pre-empt these challenges. An undocumented positive is not an unusable result; it is an avoidable credibility problem.