Urinary Biomarker

Compare creatinine-normalized and specific-gravity-normalized urinary biomarker values using caller reference SG; these corrections do not estimate exposure or set biological limits.

Description

Calculate parallel creatinine-normalized and specific-gravity-adjusted urinary biomarker concentrations.

A spot-urine concentration varies with urine dilution as well as analyte excretion. Creatinine normalization expresses analyte relative to creatinine, while specific-gravity adjustment rescales a concentration toward a chosen reference urine density. The two methods address dilution using different measurements.^{[1, 2]}

This tool returns both adjustments from the same raw analyte concentrations. They are parallel calculations, not successive corrections. Creatinine-adjusted results use µg/g creatinine; specific-gravity-adjusted results retain µg/L.

Enter analyte in µg/L and creatinine in g/L, with dimensionless sample and reference specific gravities. A corrected concentration is still a biomarker measurement rather than a reconstructed external exposure dose or a clinical diagnosis.

When to use Urinary Biomarker

Use it to compare two dilution-adjustment methods for matched samples, or reproduce a clearly specified normalization in a biomonitoring analysis.

How to use Urinary Biomarker and interpret its calculation

Enter aligned, nonempty analyteMicrogramsPerLiter, creatinineGramsPerLiter, and specificGravities lists for the same samples.
Use nonnegative analyte concentrations, positive creatinine concentrations, and specific gravities greater than one. Choose referenceSpecificGravity greater than one.
Run the calculation and compare both output lists in sample order. Keep the different output units explicit when exporting results.

Ccreatinine = C / creatinine; CSG = C × (SGreference − 1) / (SGsample − 1)

C is the original concentration in µg/L; creatinine is g/L. Both formulas start from C.

The implementation divides each raw value by its matched creatinine value and independently multiplies that raw value by the specific-gravity factor. It does not estimate a reference specific gravity from the sample set.

json

{
  "input": {
    "analyteMicrogramsPerLiter": [
      10,
      20
    ],
    "creatinineGramsPerLiter": [
      0.5,
      2
    ],
    "specificGravities": [
      1.01,
      1.02
    ],
    "referenceSpecificGravity": 1.02
  },
  "output": {
    "creatinineAdjustedMicrogramsPerGram": [
      20,
      10
    ],
    "sgAdjustedMicrogramsPerLiter": [
      20,
      20
    ]
  }
}

A sample gravity equal to the reference leaves its SG-adjusted value unchanged. Zero analyte gives zero in both outputs. Sample gravity very close to one produces a large adjustment; a gravity of exactly one is rejected. No physiological upper gravity limit is imposed by the calculation.

Limitations and assumptions

Dilution correction does not remove effects of collection time, renal function, muscle mass, analyte kinetics, or specimen contamination. The appropriate method depends on the analyte and study context.

No assay detection-limit handling, population-reference lookup, regression adjustment, or exposure reconstruction is performed. Unchecked unit substitution, especially creatinine mg/dL for g/L, changes the result.

Alternative or Complementary methods

For a molar metabolite-to-creatinine ratio, use a tool whose input and output units match that measurement. External ingestion-dose modeling can complement biomonitoring, but does not invert these corrected concentrations into a dose.

References

Urinary Creatinine Concentrations in the U.S. Population: Implications for Urinary Biologic Monitoring Measurements (Barr et al., 2005) — Environmental Health Perspectives; CDC Stacks
NIOSH Manual of Analytical Methods, Chapter F: Biological Monitoring — National Institute for Occupational Safety and Health

Similar or alternative tools

Creatinine Normalized Excretion
Calculate a molar ratio from urinary analyte µmol/L and creatinine mmol/L.
Exposure Dose
Estimate absorbed ingestion dose from external concentrations, intake, and supplied absorption fractions.