Asymptomatic Microhematuria: Why? Who? When?

What is Hematuria?

The presence of red blood cells in the urine is called hematuria when 3 or more can be counted in the high-power field (400x). Some specialized societies add more specifications to this definition: "in 3 different tests". This specifically applies to the "microscopic type", as the macroscopic (gross) type can be defined once. 

Two presentations of hematuria

Patients with gross hematuria present in many scenarios. Post-traumatic cases could show dark urine in urethral catheter. Sudden attack of bloody urine caould follow a urinary tract infection in patients under anti-coagulant therapy. Urothelial carcinoma can present with painless hematuria with no precipitation. Hematuria post-operative is a marker of hemostasis and healing in many endourology procedures.

On the other hand, an apparently clear urine could harbor few red blood cells when examined microscopically. This does not rise to patient’s awareness until a urine analysis is done for other reasons, like a routine check. Also, asymptomatic microhematuria (commonly abbreviated as AMH, for asymptomatic) could associate any of the causes that are commonly present with gross hematuria, e.g. small bladder mass, renal stone, or after trivial trauma.

The common sense about AMH is to think about glomerular disease, i.e. glomerulonephritis. Glomerulonephritides are the main scope of nephrologists, however they may occur with many vascular (hypertension, diabetic angiopathy) and rheumatologic diseases (SLE, vasculitis). Furthermore, many non-glomerular diseases could present mainly and solely with microhematuria, including papillary necrosis and drug toxicity.   

Diseases that manifest with microhematuria

Many diseases can be behind AMH. As mentioned, we can categorize them into nephrologic or urologic, and nephrologic diseases can be further categorized into glomerular and non-glomerular.

Before going deep into these, the aim of this article is to highlight the need for both nephrologists and urologists to be aware about all causes of AMH, and to practice the clinical diagnostic work up until it comes across the other specialty’s territory. Finally, patients could be referred to the corresponding clinic according to findings.

Glomerulonephritis (GN) is the main nephrologic cause of AMH. Mesangial proliferative GN, postinfectious GN, IgA nephropathy, thin basement membrane nephropathy and Alport syndrome are common causes. Loin pain hematuria syndrome is one the unexplained causes. Transient hematuria can occur in relation to exercise.

Non-glomerular include vascular diseases, for example: renal infarction, renal vein thrombosis, arteriovenous fistula or malformation. Papillary necrosis can be accompanied by AMH in diabetic patients. Radiological investigations could show cystic lesion or medullary sponge kidney. Nutcracker syndrome could be presented with microhematuria and varicocele.

Many urologic diseases could present with AMH in early phases: urinary tumors, stones, and infection. Trauma could present both gross and microscopic hematuria. Benign prostatic hyperplasia and prostatitis can be distinguished with associated urinary symptoms. Urethral infection, anomalies, diverticulum and stricture could be unusual sources.    

The aim of diagnostic workup
The main aim when investigating patients with hematuria is to identify the source of blood leakage. In microscopic hematuria we need to pass through multiple phases. First, urine tests would describe the hematuria in terms of severity and might give a hint about the source. Microscopic examination would provide data about the number of cells per high power field, and the morphologic changes in the red blood cells (disturbed cells and acanthocytosis).  The presence of casts is a mark for glomerular disease. Urine cytology might be useful to “suggest” a urothelial malignancy is high grade but cannot exclude it if negative. The presence of crystalluria is a mark of enhanced excretion of salts in urine, but it is not a good indicator for the presence of stone or its constituents. Bacteriuria is an indication for further culture and sensitivity tests.

Imaging options start from pelviabdominal ultrasound (US) and not end on pelviabdominal computed tomography (CT). US is a good test for detection of renal parenchymal disease, renal masses, renal cysts and prostatic enlargement. CT is a pivotal test for urologic diseases as the non-enhanced films are best tool for urolithiasis, the trimodal films are the best for parenchymal renal masses, while CT urography is the initial test of urothelial malignancy.

The third phase includes endoscopy (urethroscopy, cystoscopy, ureteroscopy). These procedures can be done in regional anesthesia, and some can be done at the office. Endoscopies provide the chance to visualize the luminal lesions in urethra, bladder, and ureter, respectively. They also give a chance to biopsy a suspicious lesion or completely excise it. On the other hand, renal biopsy is an important procedure if renal disease is suspected.

For further data about urologic diseases diagnosis and therapeutic options, follow our blog 

The Urologist

 

By:

Dr. Ahmed M. Bakr, MD, FEBU

References:

-        Jimbo, Masahito. "Evaluation and management of hematuria." Primary Care: Clinics in Office Practice 37.3 (2010): 461-472.

-        Bolenz, Christian, et al. "The investigation of hematuria." Deutsches Ärzteblatt International 115.48 (2018): 801.