# Corrected Calcium Calculator

> Adjusts total serum calcium for low or high albumin with the Payne formula, in conventional (mg/dL, g/dL) or SI units (mmol/L, g/L), and reports both unit systems.

- Calculator id: `corrected-calcium` · Category: Medical & Clinical (`medical`) · Tool name: `calculate_corrected_calcium`
- Canonical page: https://tttkmbb.com/medical/corrected-calcium · This document: https://tttkmbb.com/medical/corrected-calcium.md · JSON definition: https://tttkmbb.com/medical/corrected-calcium.json

## Purpose

Adjusts total serum calcium for low or high albumin with the Payne formula, in conventional (mg/dL, g/dL) or SI units (mmol/L, g/L), and reports both unit systems.

**Use when:** You have a total calcium and albumin and want the albumin-adjusted calcium used to screen for hypo- or hypercalcaemia.

**Do not use when:** An ionised calcium measurement is available (it is more accurate, especially in critical illness, acid-base disorders or renal failure).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `calcium` | number |  | required | Measured total serum calcium in the unit system chosen below. (> 0, max 20) |
| `albumin` | number |  | required | Serum albumin: g/dL for the conventional system, g/L for SI. (> 0, max 70) |
| `unit_system` | enum: conventional \| si |  | optional, default "conventional" | Units of the two inputs. |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `corrected_calcium` | number |  | Albumin-corrected calcium in the input unit. |
| `corrected_calcium_mg_dl` | number | mg/dL | Corrected calcium in mg/dL (mmol/L × 4.008). |
| `corrected_calcium_mmol_l` | number | mmol/L | Corrected calcium in mmol/L (mg/dL × 0.2495). |
| `interpretation` | string |  | Against a typical adult range of 8.5–10.5 mg/dL (2.12–2.62 mmol/L); laboratory ranges vary. |

## Formula

`Conventional: corrected_Ca (mg/dL) = calcium + 0.8 × (4.0 − albumin_g_dl). SI: corrected_Ca (mmol/L) = calcium + 0.02 × (40 − albumin_g_l). 1 mmol/L = 4.008 mg/dL.`

Payne (1973) assumes 0.8 mg/dL of calcium is bound per 1 g/dL of albumin; the correction performs poorly in chronic kidney disease and critical illness, where ionised calcium should be measured. Results are informational only and not a substitute for clinical judgement or medical advice.

## Data Sources

- Payne RB, Little AJ, Williams RB, Milner JR (1973) Interpretation of serum calcium in patients with abnormal serum proteins, Br Med J 4:643-646 — https://pubmed.ncbi.nlm.nih.gov/4758544/ (peer_reviewed, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/corrected-calcium?calcium=…&albumin=…`
- `POST https://tttkmbb.com/api/v1/calculate/corrected-calcium` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/corrected-calcium · OpenAPI operationId `calculate_corrected_calcium` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "corrected-calcium", "inputs": {…}}`

## Example

- Calcium 8.0 mg/dL, albumin 2.5 g/dL: inputs `{"calcium":8,"albumin":2.5,"unit_system":"conventional"}` → `{"corrected_calcium":9.2,"corrected_calcium_mmol_l":2.3,"interpretation":"Within the typical range (8.5–10.5 mg/dL)"}`
- Calcium 2.10 mmol/L, albumin 30 g/L: inputs `{"calcium":2.1,"albumin":30,"unit_system":"si"}` → `{"corrected_calcium":2.3,"corrected_calcium_mg_dl":9.22}`

```
GET https://tttkmbb.com/api/v1/calculate/corrected-calcium?calcium=8&albumin=2.5&unit_system=conventional
```

## Limitations

An ionised calcium measurement is available (it is more accurate, especially in critical illness, acid-base disorders or renal failure). Payne (1973) assumes 0.8 mg/dL of calcium is bound per 1 g/dL of albumin; the correction performs poorly in chronic kidney disease and critical illness, where ionised calcium should be measured. Results are informational only and not a substitute for clinical judgement or medical advice. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**My lab reports albumin in g/L; which system do I use?**

Choose si and enter calcium in mmol/L and albumin in g/L (a g/dL value × 10).

**When is the correction unreliable?**

In renal failure, after surgery, with abnormal pH, paraproteins or very low albumin the formula misclassifies many patients; ionised calcium is the reference.

## Related

- [Anion Gap Calculator](https://tttkmbb.com/medical/anion-gap.md) — Albumin also changes the expected anion gap.
- [eGFR Calculator](https://tttkmbb.com/medical/egfr.md) — Kidney function affects calcium interpretation.