False-Positive Crystals in Urine from Contamination by Multistix® 10 SG Reagent Strips for Urinalysis

Abstract

Dipstick testing of urine is commonly performed as part of point-of-care testing. Unless separate aliquots are used for dipstick testing, substances may be eluted from the test strip and contaminate patient samples. Such contamination has the potential to lead to interference in subsequent assays if the contaminated specimen is sent to the central laboratory for additional testing. We report our identification of refractile but not birefringent needle-shaped crystals as contaminants from prior contact of urine samples with the nitrite pad in the Multistix 10 SG Reagent Strips for Urinalysis (Siemens Healthcare Diagnostics, Deerfield, IL, USA). Educating clinicians who perform point-of-care testing outside the central laboratory is essential to eliminate this preanalytic artifact.