Comparing Patient-adjusted Versus Physician-adjusted Titration of BIAsp 30 Combined With Metformin in Type 2 Diabetes Patients

Inclusion Criteria: * Diagnosed with type 2 diabetes for a minimum of 12 months prior to screening * Currently treated with a NPH insulin for at least 3 months prior to screening * Stable treatment (no change in dose or regimen) with a total daily dose of at least 1500 mg metformin or maximum tolerated dose (minimum 1000 mg) ± additional OAD treatment. The metformin treatment must have been stable for at least 2 months prior to screening * HbA1c between 7.0% and 10.0% (both inclusive). (One re-test within one week of screening visit is allowed. The last sample will be conclusive.) * Body Mass Index (BMI) below or equal to 40.0 kg/m\^2 * Able and willing to eat at least 2 main meals each day during the trial * Able and willing to adhere to the protocol including compliance with performance of self measured plasma glucose (SMPG), injection regimen and titrating themselves according to the protocol * Experience in performing self-measured plasma glucose (SMPG) Exclusion Criteria: * Treatment with any thiazolidinedione (TZD) and Glucagon-like peptide-1 (GLP-1) receptor agonists or pramlintide within the last 3 months prior to screening * Impaired hepatic function defined as alanine aminotransferase (ALAT) above or equal to 2.5 times upper referenced limit. (One re-test within one week of screening visit is allowed. The last sample will be conclusive.) * Impaired kidney function with serum creatinine above or equal to 133 µmol/L (1.5 mg/dL) for males and above or equal to 124 µmol/L (1.4 mg/dL) for females. (One re-test within one week of screening visit is allowed. The last sample will be conclusive.) * Cardiac problems or uncontrolled treated/untreated severe hypertension (defined as systolic blood pressure above or equal to 180 mmHg and/or diastolic blood pressure above or equal to 100 mmHg) * Previous use of pre-mixed insulin products (pre-mixed insulin analogues or pre-mixed human preparations) * Recurrent severe hypoglycaemia (more than 1 severe hypoglycaemic episode, during the last 12 months) or hypoglycaemic unawareness as judged by the Investigator or hospitalisation for diabetic ketoacidosis during the previous 6 months * Known proliferative retinopathy or maculopathy requiring treatment