Development of an automatic laboratory computer flagging system to identify urine albumin samples potentially affected by antigen excess (‘hooking’)

Abstract

Immunoassays for urinary albumin are often subject to the problem of antigen excess (the 'hook' effect) at high albumin concentrations. We developed an automated protocol to identify such samples based on urinary albumin to creatinine ratio (uACR) and urinary total protein (uTP) results. An automated flagging system was designed and written into the laboratory computer system to alert technical staff to samples potentially affected by the 'hook effect'. This flag was activated when there was a combination of an uTP of ≥2400 mg/L and an uACR of <30 mg/mmol. The potential rate of false-negative uACR results was approximately 0.17% in samples from primary care and diabetic clinic sources. Samples with falsely low uACR results were identified, allowing the vast majority of results to be authorized without intervention. The protocol prevented the reporting of false-negative uACR results which might impact on the management of patients.