The urine chemistry survey--series 2. 5 years' experience with an interlaboratory comparison program

We have reviewed 5 years' experience with the College of American Pathologists Urine Chemistry Survey--Series 2. Analytes studied include aldosterone, total free catecholamines, the fractionated catecholamines norepinephrine, epinephrine, and dopamine, total catecholamines, estriol, 5-hydroxyindoleacetic acid, 17-ketogenic steroids, 17-ketosteroids, vanillylmandelic acid, cortisol, metanephrines, coproporphyrin, and uroporphyrin. Interlaboratory precision achieved by participants did not reach levels reported by various investigators, but their studies do not reflect actual clinical laboratory conditions. The intralaboratory analytical precision may be adequate for clinical diagnosis but better interlaboratory agreement must await the preparation of standards verified by definitive analyses. Biases introduced by the use of many different standards probably are the origin of mediocre interlaboratory proficiency testing performance.