Urinalysis for the Diagnosis of Glomerulonephritis

Role of Dysmorphic Red Blood Cells

Abdurrahman M. Hamadah; Kamel Gharaibeh; Kristin C. Mara; Katherine A. Thompson; John C. Lieske; Samar Said; Samih H. Nasr; Nelson Leung

Disclosures

Nephrol Dial Transplant. 2018;33(8):1397-1403. 

In This Article

Abstract and Introduction

Abstract

Background: Dysmorphic red blood cells (dRBCs) on urine microscopy have been associated with glomerulonephritis (GN). We assessed the prevalence and ability of dRBCs to differentiate GN from other kidney diseases.

Methods: Adult patients with kidney biopsy performed between 2012 and 2015 at a single center who had a concurrent urinalysis were retrospectively studied. The association of ≥25% dRBCs with the presence of glomerular pathology was assessed. Univariate and multivariate logistic regression were performed on significantly associated variables.

Results: The mean age of the 482 eligible subjects was 55 years and 47.7% were female. Overall, 173 (35.9%) had <25% and 76 (15.8%) had ≥25% urine dRBCs. Kidney biopsies revealed glomerular disease in 372 (77.2%) (GN 46% and non-GN 54%). At the dRBC threshold of ≥25% used at our center, a sensitivity of 20.4%, specificity of 96.3% and positive predictive value of 94.6% for glomerular disease were observed. In a logistic regression model, urine RBCs [>10 versus ≤10 (P < 0.001)] but not dRBCs ≥25% (P = 0.3) independently predicted the presence of GN. A scoring system (0–3) based on hematuria and proteinuria levels revealed the risk for biopsy-proven GN was 15% when the score was 0 compared with 83% when it was 3.

Conclusions: The presence of ≥25% urine dRBCs is specific but not sensitive for GN. In this cohort, the combined hematuria (>10 RBCs/high-power field) and proteinuria performed just as well as dRBCs plus proteinuria to predict underlying GN. A model based on the degree of hematuria and proteinuria found on urinalysis was able to predict the presence of GN.

Introduction

Urinalysis with microscopy remains an essential tool for timely diagnosis and management of kidney diseases.[1,2] The presence of dysmorphic red blood cells (dRBCs) has been associated with glomerular diseases (GDs) and thus is reported by some laboratories. In 1979, Birch and Fairly initially described the distorted morphology of RBCs seen under phase contrast microscopy that they associated with glomerular bleeding, coining the term dRBC.[3,4] Phase contrast microscopy offers the best ability to discriminate urinary sediment elements and is felt to be superior to bright field microscopy for this purpose.[4–6] Up to nine different morphologies of dRBCs have been described in the literature.[7–10] Of these, acanthocytes seem most specific for GD.[8] A recent report suggested that urinary acanthocytes associate with proliferative lesions on renal biopsies of lupus nephritis patients.[11] However, the exact morphologies used to categorize dRBCs and the number needed to make disease associations has not been standardized, likely impacting its sensitivity and specificity.[1] Depending on the study design and selected population, the clinical cutoff for significant dRBCs in the literature varies between 10% and 90%.[12] Factors that have impacted the interpretation of these studies include the relatively small size, small number of biopsy proven kidney disease entities and sometimes the use of clinically established (rather than biopsy-proven) diagnoses.[7,9,12–14] Our laboratory has used a standard approach to identify dRBCs in any urinalysis with microscopic hematuria since 1998 and reports whether the total exceeds 25% of all RBCs observed. This provided an opportunity to evaluate the clinical utility of dRBCs assessed in a standardized way in a consecutive cohort over many years. In the current study, we retrospectively analyzed the association of dRBCs and renal pathology in a large cohort of patients that had available renal biopsies. Our objectives were to assess the prevalence of dRBCs in common kidney diseases and the factors that determine their presence and to establish whether the presence of dRBCs differentiates between glomerular and nonglomerular processes. Additionally, we investigated whether other elements of a standard urinalysis associated with a pathologic diagnosis of GN.

Comments

3090D553-9492-4563-8681-AD288FA52ACE

processing....