# Sickle Cell RBC Exchange Replacement Volume Calculator

> Sickle Cell RBC Exchange Replacement Volume Calculator is a paid API for AI agents from api.magentlab.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-15).

Calculates the replacement packed RBC volume needed for a sickle cell exchange transfusion using Nadler 1962 blood volume estimation and exponential HbS washout arithmetic

## Facts

- Endpoint: GET https://api.magentlab.com/api/calc/sickle_rbc_exchange
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/sickle-cell-rbc-exchange-replacement-volume-calculator-e3e78e3e
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_7GaqKyCzaMboHtL8dhydR

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability sickle-cell-rbc-exchange-replacement-volume-calculator-e3e78e3e
```

Example prompt: Calculate the replacement pRBC volume for a sickle cell exchange transfusion for a male patient who is 175 cm tall, weighs 80 kg, with a current hematocrit of 28%, initial HbS of 85%, a target HbS of 30%, and replacement unit hematocrit of 60% — and tell me how many 350 mL units that comes to.

## When to prefer this

Use this endpoint when you need a deterministic, arithmetic calculation of replacement pRBC volume for a manual or apheresis sickle cell red cell exchange, based on Nadler 1962 blood volume and exponential HbS washout. It is the right choice when you already have patient anthropometrics, starting and target HbS values, and replacement unit hematocrit, and need a published, reproducible formula result — not a clinical recommendation or device order.

## Known failure modes

- Missing required parameters (sex, hematocrit_percent, initial_hbs_percent, target_hbs_percent, replacement_hct_percent) returns validation error
- target_hbs_percent >= initial_hbs_percent returns error — target must be strictly less than initial
- hematocrit_percent outside 10–70 range rejected
- replacement_hct_percent outside 50–80 range rejected
- unit_volume_ml outside 50–500 range rejected
- Neither height nor weight provided — blood volume cannot be estimated
- Implausible height/weight combinations may produce unrealistic blood volume estimates

## How this service works

Nadler 1962 adult blood volume plus exponential remaining-fraction washout (Y/Y0 = e^(−X)) for sickle RBC exchange replacement pRBC volume. FCR = target_hbs / initial_hbs; X = −ln(FCR). Caller supplies hematocrits and HbS percents. Optional approx units if unit_volume_ml is sent. Deterministic published arithmetic. Not an apheresis order or medical device.

## Output

Returns computed total blood volume (mL), the fraction change ratio (FCR = target_hbs/initial_hbs), the washout exponent X, the required replacement pRBC volume in mL, and optionally the approximate number of standard units if unit_volume_ml is provided.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "headers": {
     "type": "object",
     "additionalProperties": {
      "type": "string"
     }
    },
    "queryParams": {
     "type": "object",
     "required": [
      "sex",
      "hematocrit_percent",
      "initial_hbs_percent",
      "target_hbs_percent",
      "replacement_hct_percent"
     ],
     "properties": {
      "sex": {
       "enum": [
        "female",
        "male"
       ],
       "type": "string",
       "description": "Sex used by Nadler 1962 (separate male and female equations)."
      },
      "height_cm": {
       "type": "number",
       "description": "Height in centimeters. Provide height_cm or height_in."
      },
      "height_in": {
       "type": "number",
       "description": "Height in inches. Converted as cm = in * 2.54."
      },
      "weight_kg": {
       "type": "number",
       "description": "Weight in kilograms. Provide weight_kg or weight_lb."
      },
      "weight_lb": {
       "type": "number",
       "description": "Weight in pounds. Converted as kg = lb * 0.45359237."
      },
      "unit_volume_ml": {
       "type": "number",
       "description": "Optional caller-assigned unit volume in mL (50-500). When sent, response includes approx_units = replacement_prbc_ml / unit_volume_ml."
      },
      "hematocrit_percent": {
       "type": "number",
       "description": "Patient hematocrit as a percent (10-70). Required. Not a 0-1 fraction."
      },
      "target_hbs_percent": {
       "type": "number",
       "description": "Target HbS percent (1-100). Required. Must be strictly less than initial_hbs_percent. AABB 2018 usual goal language is HbS not more than 30%; the caller sends this value."
      },
      "initial_hbs_percent": {
       "type": "number",
       "description": "Initial HbS percent (1-100). Required. Must be greater than target_hbs_percent."
      },
      "replacement_hct_percent": {
       "type": "number",
       "description": "Replacement packed-RBC hematocrit as a percent (50-80). Required. Typical additive units are about 60. magent does not assay the unit."
      }
     }
    }
  
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/sickle-cell-rbc-exchange-replacement-volume-calculator-e3e78e3e/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.magentlab.com](https://www.zero.xyz/host/api.magentlab.com/llms.txt)