Microscopic Hematuria: Those Pesky RBCs

What is microscopic hematuria?

The American Urological Association (AUA) defines microscopic hematuria as ≥3 red cells per high power field. 

Clinicians should NOT diagnose microhematuria on dipstick testing alone. A positive urine dipstick test (trace blood or greater) should prompt formal microscopic evaluation of the urine. (Strong Recommendation; Evidence Level: Grade C)

Guidelines: Old & New

The 2012 AUA Guidelines on Diagnosis, Evaluation and Follow-up of Asymptomatic Microhematuria in Adults recommended that all patients older than 35yo with microscopic hematuria should undergo both CT urography and cystoscopy

  • CT urography = CT of the kidneys, ureters and bladder with ≥1 series of images acquired during the excretory phase after IV contrast administration

The more recent 2020 AUA Guideline on Microhematuria features a few key updates:

  • In patients with microhematuria, clinicians should perform a thorough history and physical to assess risk factors for GU malignancy, medical renal disease, gynecologic, and nonmalignant GU causes of hematuria 
  • History/exam should be performed regardless of whether or not the patient is taking antiplatelet medications or anticoagulation
  • Classifies patients into 3 categories of risk for GU malignancy:
    • Low Risk: Repeat UA at 6 months or proceed with renal US and cystoscopy (either option is acceptable)
    • Intermediate Risk: Renal US and cystoscopy
    • High Risk: CT Urography and cystoscopy

Key point: Women with hematuria have been especially prone to delays in evaluation, often due to practitioners ascribing hematuria to a UTI or gynecologic source, resulting in inadequate evaluation and delay in cancer diagnosis. 

Why the move AWAY from CT urography?

In 2019, Smith et al reported data from an integrated medical system in which US was the initial upper urinary tract imaging procedure for 2100 adults who had asymptomatic microscopic hematuria and were followed for at least 3 years.

  • No important upper tract malignancies were missed by this approach
  • US imaging detected suspicious findings in 9 of 9 patients with RCC and 3 of 3 patients with upper tract urothelial cancer (sensitivity of 100% and 100%, respectively)

In 2020, Rabinowitz et al validated a previously published “hematuria risk index” in 1000 patients with asymptomatic microscopic hematuria. 

  • Hematuria risk index: low-risk group had a 0-0.3% rate of cancer detection, moderate risk 1.1-2.5% rate, and high risk 10.7-11.6%
  • Among 600 patients classified as low risk, half had CT urography, and half had renal ultrasound; no upper tract cancers were found by either imaging modality

These studies suggest that renal ultrasound is an acceptable way to examine kidneys in many patients with asymptomatic microscopic hematuria.

  • Limits exposure to radiation and contrast
  • Less expensive than CT urography

Other causes of microscopic hematuria?

Assess for gynecologic or non-malignant urologic etiologies.

After diagnosis of gynecologic or non-malignant GU sources of microhematuria, clinicians should repeat UA following resolution of the gynecologic or non-malignant GU cause.

  • If microhematuria persists or etiology cannot be identified, clinicians should perform risk-based urologic evaluation.

In patients with hematuria attributed to a UTI, clinicians should obtain UA with microscopic evaluation following treatment to ensure resolution of hematuria.

Clinicians should refer patients with microhematuria for nephrologic evaluation if medical renal disease is suspected. However, risk-based urologic evaluation should still be performed.

A Case!

37yo male comes to the Med-Peds Clinic to see you for mild intermittent dysuria. You obtain a urine dipstick, which is unremarkable except for trace blood.

What do you do now?

  • Send for microscopic UA
  • Recall that you cannot diagnose microscopic hematuria on dipstick alone; a positive urine dipstick test (trace blood or greater) should prompt formal microscopic evaluation of the urine

Additional history: He denies gross hematuria or history of tobacco use. Microscopic evaluation of UA shows 0 WBCs and 20 RBCs.

What risk category does this patient fall in and what should you do next?

  • 1 point (male) → Low risk
  • Repeat UA in 6 months. (It is also acceptable to obtain renal US and cystoscopy)

What risk level would the patient be if he was >50 yo and had a history of tobacco use, but still no gross hematuria and 20 RBCs on UA?

  • 6 points (age, tobacco, male) → Intermediate risk
  • Perform renal US and cystoscopy

What diagnostic testing would you order if the patient was high risk?

  • CT Urography and cystoscopy

Take-Home Points!

  • Confirm hematuria on dipstick with microscopic UA
  • Evaluate for causes of hematuria such as malignant GU, renal, gynecologic, and non-malignant GU etiologies
  • Repeat UA when nonmalignant GU or gyn causes have been treated/resolved
  • Risk stratify patients with hematuria
  • Low risk: repeat UA in 6 months or obtain renal US and cystoscopy
  • Intermediate risk: renal US and cystoscopy
  • High risk: CT urography and cystoscopy

Blog post based on Med-Peds Forum talk by Ann Ding, PGY3

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