Borderline Lab Values

A laboratory result just beyond a printed reference interval is a signal to interpret, not a diagnosis. Reference intervals are usually derived from the central 95% of a healthy reference population, so approximately 1 in 20 healthy people will fall outside any single interval. The chance of an incidental flag increases as more analytes are measured. The reverse is also true: a result inside the interval can still be clinically important if it has changed substantially from the patient's baseline or crossed a disease-specific decision threshold. An experienced NP first asks whether the specimen is trustworthy, whether the result fits the patient's symptoms and physiology, and how it compares with prior testing. Collection conditions, medications, acute illness, age, pregnancy, biological variation, and assay interference can all move a result without establishing disease. The next question is whether the finding needs confirmation, trend assessment, immediate treatment, or simply observation. Canadian practice also requires unit discipline. Apply local SI reporting when interpreting this topic: glucose is reported in mmol/L, creatinine in micromol/L, and urine albumin-to-creatinine ratio in mg/mmol. Canadian prediabetes is A1C...