  List<clsPatientModel> searchResult = new List<clsPatientModel>();
 
                searchResult = searchResult
                                   .Concat(
                                           from patient in patients
                                           where patient.DateEntry.EntryDate.Date == Convert.ToDateTime(dptEntryDate.Value.Date)
                                           select patient)
                                   .ToList();
 
                searchResult = searchResult
                                    .Concat(
                                            from patient in patients
                                            where patient.PatientDetails.DOB.Date == Convert.ToDateTime(dpDOB.Value.Date)
                                            select patient)
                                    .ToList();
 
                if (!string.IsNullOrWhiteSpace(txtSurname.Text))
                {
                    searchResult = searchResult
                                    .Concat(
                                            from patient in patients
                                            where patient.PatientDetails.Surname.ToLowerInvariant().Contains(txtSurname.Text.ToLowerInvariant().Trim())
                                            select patient)
                                    .ToList();
                }
 
                if (!string.IsNullOrWhiteSpace(txtName.Text))
                {
                    searchResult = searchResult
                                    .Concat(
                                            from patient in patients
                                            where patient.PatientDetails.Name.ToLowerInvariant().Contains(txtName.Text.ToLowerInvariant().Trim())
                                            select patient)
                                    .ToList();
                }

	List<clsPatientModel> searchResult = new List<clsPatientModel>();

	searchResult = searchResult
	.Concat(
	from patient in patients
	where patient.DateEntry.EntryDate.Date == Convert.ToDateTime(dptEntryDate.Value.Date)
	select patient)
	.ToList();

	searchResult = searchResult
	.Concat(
	from patient in patients
	where patient.PatientDetails.DOB.Date == Convert.ToDateTime(dpDOB.Value.Date)
	select patient)
	.ToList();

	if (!string.IsNullOrWhiteSpace(txtSurname.Text))
	{
	searchResult = searchResult
	.Concat(
	from patient in patients
	where patient.PatientDetails.Surname.ToLowerInvariant().Contains(txtSurname.Text.ToLowerInvariant().Trim())
	select patient)
	.ToList();
	}

	if (!string.IsNullOrWhiteSpace(txtName.Text))
	{
	searchResult = searchResult
	.Concat(
	from patient in patients
	where patient.PatientDetails.Name.ToLowerInvariant().Contains(txtName.Text.ToLowerInvariant().Trim())
	select patient)
	.ToList();
	}