Source: https://guthlabs.ai/docs/instruments/osmolarity-tonicity-calculator/

instrument / verified-clean

# Osmolarity / Tonicity Calculator

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Inspectable records

[01**Overview**Purpose and lifecycle](<https://guthlabs.ai/docs/instruments/osmolarity-tonicity-calculator/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/osmolarity-tonicity-calculator/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/osmolarity-tonicity-calculator/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/osmolarity-tonicity-calculator/qualification/>)

## Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

**Area**: Biology, Medicine & Pharmacology (educational estimates only — every panel labeled not-medical-advice)

**Tranche**: tranche-4

**Evidence ID**: t4-170

**Ledger rows**: 1

No ledger note is attached.

## Review findings

Educational estimate only and not medical advice. Before release, explicitly separate solution osmolarity from serum osmolality, document all required units, add the ×1000 conversion for solution results, and either remove the tonicity label or define the reference solution, effective-solute model, and labeling rules.

### Formula and scope findings

- The osmolarity formula is dimensionally correct when molarity is in mol/L and dissociation factor is dimensionless, but the stated output unit mOsm/L requires multiplying the result in Osm/L by 1000; this conversion is not stated.

- The serum formula 2Na+Glucose/18+BUN/2.8 is a standard estimated serum osmolality formula, not serum osmolarity. Its result is conventionally mOsm/kg, while the output specification says mOsm/L.

- The serum formula is valid only when Na is in mmol/L (numerically equivalent to mEq/L for sodium), and glucose and BUN are in mg/dL. The required units are not stated in the formula or inputs.

- An isotonic/hypertonic/hypotonic label cannot be determined from total osmolarity alone: the reference value, membrane permeability, effective osmoles, and comparison context are unspecified. Total osmolarity can indicate hypo-osmotic or hyper-osmotic status, which is not necessarily tonicity.

- The solution formula assumes ideal behavior and complete dissociation according to the supplied factor; activity coefficients and partial dissociation are ignored. The instrument does not state this assumption.

### Unit assumptions

- Solution solute concentrations are mol/L (M), and dissociation factors are dimensionless.

- Solution output is converted from Osm/L to mOsm/L by multiplying by 1000.

- For the serum estimate, Na is in mmol/L, glucose is in mg/dL, and BUN is in mg/dL.

- The serum estimate output is interpreted as mOsm/kg, because the formula estimates osmolality rather than osmolarity.

- BUN means blood urea nitrogen, not urea concentration; substituting urea requires a different coefficient or unit handling.

- Tonicity cannot be assigned without specifying the reference solution and which solutes are effectively nonpenetrating across the relevant membrane.

## Boundary hardening

**BREAK_CLAIMED** · SELF_FLAGGED

The plain-arithmetic implementation can return Infinity for extreme finite inputs instead of rejecting them. The specification also omits the tonicity reference threshold and explicit concentration units, allowing classification and numerical interpretation ambiguities.

## Errata and corrections

No applied erratum is attached to this unique-name record.

## Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

````
{
  "inputs": {
    "mode": "solution",
    "solutes": [
      {
        "name": "NaCl",
        "molarity_mol_per_L": 0.154,
        "dissociation_factor": 2
      }
    ]
  },
  "expected_outputs": {
    "osmolarity_Osm_per_L": 0.308,
    "osmolarity_mOsm_per_L": 308,
    "tonicity_label": "not determinable from total osmolarity alone"
  },
  "working": "Osm = 0.154 mol/L × 2 = 0.308 Osm/L. Convert to mOsm/L: 0.308 × 1000 = 308 mOsm/L. A tonicity label is not assigned because membrane permeability and the reference condition are unspecified."
}
````

## Related workflows

[Renal Dosing Chain (education)labs context](<https://guthlabs.ai/docs/instrument-workflows/renal-dosing/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json · VERIFIED_CLEAN`

- `evidence-tranche4/tranche4-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`