Laboratory diagnosis and monitoring of diabetes mellitus.

The American Diabetes Association emphasizes fasting plasma glucose (FPG) levels, rather than the oral glucose tolerance test (OGTT), to diagnose diabetes mellitus. The diagnostic cutoff for FPG is 126 mg/dL (7.0 mmol/L). A 2-hour plasma glucose level of 200 mg/dL (11.1 mmol/L) or more during an OGTT or a random plasma glucose level of 200 mg/dL (11.1 mmol/L) or more also is diagnostic of diabetes. The 100-g, 3-hour OGTT remains the "gold standard" for gestational diabetes mellitus (GDM). Two of 4 samples exceeding cutoffs (fasting, > or = 105 mg/dL [5.8 mmol/L]; 1 hour, > or = 190 mg/dL [10.5 mmol/L]; 2 hours, > or = 165 mg/dL [9.2 mmol/L]; 3 hours, > or = 145 mg/dL [8.0 mmol/L]) indicate GDM. An effective GDM screening test is plasma glucose 1 hour after a 50-g oral glucose load. Tight control, which requires self-monitoring of blood glucose, reduces microvascular complications for patients with type 1 or type 2 diabetes. Patients with well-controlled diabetes have glycohemoglobin concentrations of 7% AIc (0.07 AIc/A) or less. Microalbuminuria indicates early, reversible, diabetic nephropathy. The random urine albumin-creatinine ratio is a convenient effective screening test. Albumin-creatinine ratios in the 0.03 to 0.30 (g/g) range indicate microalbuminuria.