A blood-cell ratio measured alongside a positive urine screen can reveal an association without identifying the drug responsible or the cause of the blood finding. A 2026 hospital laboratory study illustrates the importance of keeping analytical class, specimen, comparison group and causal interpretation distinct.
What did the laboratory dataset contain?
Lara-Apolinario and colleagues analyzed 5,008 samples from 2021–2025 with at least one positive drug-class screen and a concurrent blood count. The amphetamine/methamphetamine immunoassay cutoff was 500 ng/mL in urine. Among single-class-positive samples, the amphetamine group comprised 487, with median neutrophil-to-lymphocyte ratio (NLR) 3.28; the cannabis group comprised 1,831, with median 2.39. Lara-Apolinario et al., 2026.
NLR was calculated from absolute blood neutrophil and lymphocyte counts. Substance-type comparisons were unadjusted. Clinical diagnoses, comorbidities and some co-exposures were unavailable; testing indications could differ between groups, and immunoassays could misclassify exposure. The article was published on October 8, 2026. Methods, results and limitations.
Why is the urine result a class finding?
The analyzed exposure category was amphetamine/methamphetamine immunoreactivity. It was not a quantitatively confirmed methamphetamine blood concentration. Describing the category as methamphetamine alone would make the exposure more specific than the study’s classification supports.
The screen cutoff also belongs to urine, while NLR belongs to a blood count. Their appearance in the same record does not make them measurements of the same biological quantity. A urine threshold cannot serve as an inflammatory-effect threshold or an impairment threshold.
What can a ratio hide?
A ratio can rise because its numerator increases, its denominator decreases or both change. As a purely arithmetic example, four divided by two equals two; four divided by one equals four. The ratio doubles despite an unchanged numerator.
Consequently, a higher NLR alone does not identify which cell population drove the difference or establish the mechanism. Reviewing the component counts and clinical setting is more informative than assigning every ratio change to one drug effect.
Why does the unadjusted comparison matter?
The groups may differ in characteristics that also relate to the blood count. Measuring exposure and NLR during one encounter does not establish the temporal sequence needed for a drug-caused inflammatory response. Missing clinical context makes those competing explanations harder to evaluate.
A regression using age, sex and the number of detected substances is not the same analysis as an adjusted causal comparison between specific substance types. The distinction should remain explicit when a headline moves from “higher in this group” to “this drug caused more inflammation.”
Does a sample count equal a population risk estimate?
The dataset begins with selected drug-screen-positive samples that also had blood testing. It therefore does not describe all people using amphetamines or the probability of inflammation after a particular dose. The sampling pathway belongs beside the large denominator.
The study supports a hypothesis about differences worth investigating. It does not validate NLR as a methamphetamine exposure test, diagnose a substance-use disorder from a blood count or demonstrate clinical injury caused by an individual exposure. Those claims require separate validation and case-specific evidence.
Source
Lara-Apolinario C, Martinez-Carral C, Fischetti D, Fulgencio-González AJ, Domínguez C, Lara PC. Differential Effect of Abusing Substances Alone or in Combination in Systemic Inflammation. Medicina. 2026;62:1939. doi:10.3390/medicina62101939. Retrospective observational laboratory study.