# Example: referral checker

URL: https://docs.healthcare.dev/agents/referral-checker

Checks the structured parts of a referral: the receiving provider's NPI and the ICD-10-CM codes.
It works on identifiers only; patient details never leave your system.

```ts
import { HealthcareDev, isValidNpi } from "@healthcare.dev/sdk";

const hdev = new HealthcareDev();

export async function checkReferral(input: { npi: string; diagnosisCodes: string[] }) {
  const issues: string[] = [];
  if (!isValidNpi(input.npi)) issues.push(`NPI ${input.npi} fails the check digit`);

  const { data, meta } = await hdev.codes.batch("icd10cm", input.diagnosisCodes);
  for (const r of data) {
    if (!r.found) issues.push(`${r.code} is not an ICD-10-CM code`);
    else if (r.record && !r.record.billable)
      issues.push(`${r.code} is a header code; pick a more specific child`);
    else if (r.record && r.record.status !== "active")
      issues.push(
        `${r.code} is ${r.record.status}; replaced by ${r.record.replaced_by.join(", ") || "nothing listed"}`,
      );
  }
  return { ok: issues.length === 0, issues, cite: `${meta.source} ${meta.data_version}` };
}
```

With MCP, give the agent `validate_npi`, `lookup_code` and `explain_code_hierarchy` and the
instruction: _"Check each code is billable and active; suggest children for header codes; never
choose a diagnosis yourself."_