Question 1. What is the laboratory definition of chronic kidney disease?
Chronic kidney disease (CKD) is defined as abnormalities of kidney structure or function, present for >3 months, withimplications for health.1 CKD can be diagnosed based on a glomerular filtration rate (GFR) <60 mL/min/1.73 m2 for >3 months, evidence of kidney damage for >3 months, or both.1
GFR is considered the best overall laboratory marker of kidney function.1 Because direct measurement of GFR can be problematic, an estimated GFR (eGFR) determined using creatinine- or cystatin C-based measurements is most commonly used to diagnose CKD in clinical practice. The Kidney Profile (test code 39165) incorporates creatinine-based eGFR.
Indications of kidney damage include a histologic abnormality, structural abnormality, history of kidney transplantation, abnormal urine sediment, tubular disorder-caused electrolyte abnormality, or an increased urinary albumin level (albuminuria). A urine albumin-creatinine ratio ≥30 mg/g (μg/mg) is considered evidence of albuminuria consistent with kidney damage.
Note that terminology has standardized to define a urine albumin-creatinine ratio result of ≥30 mg/g (albumin excretion rate ≥30 mg/24 h) as evidence of albuminuria; formerly, a ratio of 30-300 mg/g was referred to as “microalbuminuria,” and a ratio of >300 mg/g was defined as “macroalbuminuria.”1