I would do it this way:
using Microsoft.TeamFoundation.Client;
using Microsoft.TeamFoundation.TestManagement.Client;
var tfsCollection = new TfsTeamProjectCollection(
new Uri(@"http://<yourTFS>:8080/tfs/<your collection>"),
new System.Net.NetworkCredential(<user who can access to TFS>,<password>));
tfsCollection.EnsureAuthenticated();
ITestManagementService testManagementService = tfsCollection.GetService<ITestManagementService>();
var testRuns = testManagementService.QueryTestRuns("SELECT * FROM TestRun WHERE TestRun.TestPlanId=<your test plan ID>");
IEnumerable<ITestCaseResult> testResultHistoryYouWant = from testRun in testRuns
from testResult in testRun.QueryResults()
where testResult.TestCaseId == <your test case ID>
select testResult;