Reference
How Detection Level works
Detection Level, or DL, is the semi-quantitative scale OraPath uses to report how much of a target organism's DNA was found in a saliva sample. It is calculated as DL = 40 − Ct, where Ct is the qPCR cycle threshold. Each additional Detection Level represents roughly twice as much target DNA, and DL 0 means the target was not detected. DL describes a sample, not a person, and is read alongside a clinician's examination.
Why not report a concentration
qPCR does not measure a quantity directly. It measures how many amplification cycles it takes before a target's signal rises above background — the cycle threshold, or Ct. A sample with more starting DNA crosses that threshold sooner, so a lower Ct means more organism.
Reporting Ct raw has a readability problem: the scale runs backwards, and a smaller number means a bigger finding. Subtracting it from 40 flips the axis. DL rises as the organism rises, which is the direction a reader expects.
DL is deliberately called a Detection Level and not a concentration or an abundance. It is semi-quantitative: it supports comparison between samples run the same way, and it is not a count of organisms per millilitre.
What "each step doubles" means
DL is a log₂ scale, because each qPCR cycle approximately doubles the DNA present. One Detection Level up is therefore about twice as much target DNA, not one unit more of something.
This matters most when comparing two results. The gap between DL 10 and DL 14 is not “four more” — it is roughly sixteen times more. A reader who treats DL as a linear score will badly underestimate what a four-point move represents.
The same property is what makes a retest legible. A follow-up sample run on the same panel can be compared to the first directly, and a change of one or two Detection Levels is a real change in quantity rather than analytical noise.
Detection Level bands by category
Category cutoffs are not the same. A DL of 8 is a different finding depending on what was detected.
Bands as printed on the Oral Balance report. DL 0 means not detected.
| Category | Trace | Low | Moderate | High |
|---|---|---|---|---|
| Periodontal | >0–<3 | 3–<10 | 10–<14 | ≥14 |
| Caries | >0–<3 | 3–<6 | 6–<10 | ≥10 |
| Fungal | >0–<3 | 3–<6 | 6–<12 | ≥12 |
| Protective | >0–<3 | 3–<12 | 12–<18 | ≥18 |
A. actinomycetemcomitans is the exception. It is associated with periodontal disease at much lower abundance than the other periodontal targets, so its bands are tightened — Moderate at ≥4 and High at ≥8, against ≥10 and ≥14 for the rest of the category.
Reading the protective side
The protective category — the commensal streptococci and the narG-carrying nitric-oxide group — uses the widest bands on the panel, and it is the one category where a higher Detection Level is the result a clinician is generally looking for.
That inversion is why the report separates protective capacity from disruptive pressure rather than summing everything into one number. A high DL is not good or bad on its own; what it means depends entirely on which target it belongs to.
Why DL 0 is "not detected", not "zero"
DL 0 means the assay did not detect the target in that sample above its limit of detection. It does not establish that the organism is absent from the mouth.
A target can go undetected because it is genuinely not present, because it is present below the assay's threshold, or because of how and when the sample was collected. This is why a result is interpreted alongside an examination rather than read as a census.
What a Detection Level does not tell you
A Detection Level is a measurement of one target in one saliva sample at one point in time. It is not a diagnosis, it does not establish that an organism is causing anything a patient is experiencing, and it does not predict what will happen next.
Detection Levels are reported to support a clinician's assessment, not to replace an examination. A finding worth acting on is a finding worth discussing with your dentist.