component.ts

import { Component, OnInit, OnDestroy } from '@angular/core';
import { SubscriptionManager } from 'path/to/subscription_manager';

@Component({
  selector: 'app-thing',
  templateUrl: './app-thing.component.html',
  styleUrls: ['./app-thing.component.scss']
})
export class PatientReviewComponent implements OnInit, OnDestroy {
  public isLoading: boolean = true;
  private Id: number;
  private subscriptions: SubscriptionManager = new SubscriptionManager();

  constructor(private service: Service) { }

  private loadData(): void {
    let sub = this.service.getQuestions(this.Id)
      .subscribe(
        (res: any) => {
          this.data = res;
        });
    this.subscriptions.add(sub);
  }

  ngOnInit() {
    this.loadData();
  }

  ngOnDestroy() {
    this.subscriptions.destroy();
  }
}

service.ts

public getQuestions(Id: number): Observable<any[]> {
    let url = '/endpoint';
    let params: URLSearchParams = new URLSearchParams();
    params.set('api_key', this.config.api_key);
    let options: RequestOptions = new RequestOptions({search: params});

    return this.api
      .get(url, options)
      .map(res => this.mapQuestionData(res))
      .catch(error => this.handleError(error));
  }

subscription_manager.ts

export class SubscriptionManager {
  private subscriptions: any[] = [];

  public add(sub: any) {
    this.subscriptions.push(sub);
  }

  public destroy(): void {
    this.subscriptions.forEach((sub: any) => sub.unsubscribe());
    this.subscriptions = [];
  }
}