Hello! Welcome back to our module on Renal Function and Urinalysis.
In our last lesson, we delved into the details of urine microscopy, learning how to identify cells, casts, and crystals. You learned that specific findings, like dysmorphic red blood cells (RBCs) and RBC casts, are powerful clues that point towards disease within the kidney itself.
Today, we will apply that knowledge to a very common and important clinical presentation: hematuria (blood in the urine). Our goal is to master how to differentiate glomerular from non-glomerular hematuria using urinalysis findings. This is a critical step in any hematuria workup, as it immediately narrows the vast list of potential causes and directs your subsequent investigation toward either nephrology (for glomerular causes) or urology (for non-glomerular causes).
The First Crucial Question: Where is the Bleeding From?
When a patient has hematuria, the first question to answer is whether the bleeding originates from the glomeruli (the kidney's filtering units) or from somewhere else in the genitourinary (GU) tract.
- Glomerular hematuria is caused by damage to the glomeruli themselves, often from inflammatory conditions called glomerulonephritis.
- Non-glomerular hematuria can originate from anywhere "downstream" of the glomerulus: the renal tubules, renal pelvis, ureters, bladder, or urethra. Causes are diverse, including infections, stones, and malignancies.
To get an overview of this framework and the common causes in each category, watch the following short clip.
This video from Strong Medicine clearly explains the fundamental division between glomerular and non-glomerular bleeding and lists the main etiologies for each.
Watch from 1:29 to 4:06. Focus on understanding the anatomical distinction and the general categories of disease that cause each type of bleeding. You don't need to memorize every single cause right now.
Deciphering the Clues: Urinalysis Findings
The urine itself holds the key to differentiating the source of bleeding. As RBCs pass through a damaged glomerulus and a long, narrow tubule, they become misshapen and can get trapped in casts. In contrast, if blood is simply mixing with urine in the bladder, the RBCs remain normal-shaped. This is the central principle we use.
The following image provides an excellent side-by-side comparison of the microscopic findings.
Here is a summary of the classic urinalysis patterns:
| Urinalysis Finding | Glomerular Hematuria | Non-Glomerular Hematuria | Why? |
|---|---|---|---|
| RBC Morphology | Dysmorphic (misshapen, "Mickey Mouse" cells) | Isomorphic (normal, biconcave discs) | Glomerular RBCs are damaged passing through the glomerular basement membrane. |
| RBC Casts | Present | Absent | Casts are formed in the renal tubules; their presence proves the bleeding is from the kidney parenchyma. |
| Proteinuria | Often significant (>300 mg/day or 2+) | Typically absent or minimal (<300 mg/day or trace/1+) | The glomerular damage that allows RBCs to leak also allows protein (like albumin) to leak. |
| Blood Clots | Absent | May be present (especially in gross hematuria) | Clots can form in the bladder or renal pelvis but are too large to form in the microscopic tubules. |
The following video clips provide a clear explanation of how to use these findings to make the distinction.
Hematuria Causes & Diagnostic Workup of Blood in Urine
The first video, from MedNerd, focuses on the classic signs of glomerular injury.
Watch from 1:02 to 2:42. Dr. Fazal does an excellent job explaining why you see dysmorphic RBCs, RBC casts, and proteinuria in glomerular disease.
This second clip, from Strong Medicine, concisely contrasts the urinalysis findings for both types of bleeding.
Watch from 10:31 to 11:06 and then from 11:22 to 11:51. This effectively summarizes the entire diagnostic logic based on the urinalysis.
To solidify this knowledge, let's turn to a more detailed textual resource.
Approach to the Patient with Hematuria
The article 'Approach to the Patient with Hematuria' provides an excellent, in-depth explanation of this diagnostic process. It also includes two case studies that demonstrate how these principles are applied in practice.
Please read the following sections: Start with the section titled 'Evaluate for Glomerular Hematuria.' This is the most important part and directly addresses today's topic. Next, read the sections for 'Case 1' and 'Case 2' to see how a clinician thinks through the initial presentation. Finally, read the resolutions to Case 1 and Case 2 at the end of the article to see how the urinalysis findings directly guided the next steps and ultimate diagnosis.
Test your understanding!
A 25-year-old woman presents with cola-colored urine, facial puffiness, and a blood pressure of 150/95 mmHg. Her urinalysis report shows:
- Color: Dark brown
- Blood: 3+
- Protein: 2+
- Microscopy: >100 RBCs per high power field, numerous RBC casts, and dysmorphic RBCs.
Is this hematuria more likely to be glomerular or non-glomerular in origin? What features lead you to that conclusion?
Show answer
This is classic glomerular hematuria. The key findings are the presence of RBC casts (which are pathognomonic for glomerular disease) and dysmorphic RBCs. The significant proteinuria (2+) and hypertension also strongly support a glomerular source, pointing towards a nephritic syndrome.
A Framework for Clinical Practice
Now that you can distinguish between glomerular and non-glomerular patterns on a urinalysis, you can see how this fits into the overall diagnostic workflow for a patient with hematuria. The presence or absence of those key findings dictates the entire subsequent workup.
As the flowchart and the case studies show, if signs point to a glomerular source, the workup involves serologic tests for autoimmune diseases and glomerulonephritis, followed by a referral to a nephrologist, who may consider a kidney biopsy.
If the signs point to a non-glomerular source (isomorphic RBCs, no casts), the workup focuses on finding a structural cause. This involves imaging of the urinary tract (like a CT scan or ultrasound) and often a cystoscopy (a camera examination of the bladder) performed by a urologist.
Conclusion
You have now learned a fundamental skill in renal diagnostics. By carefully examining a urinalysis report, you can make a confident and critical distinction between bleeding that originates from the glomeruli and bleeding that comes from elsewhere in the urinary tract.
Key Takeaways:
- The primary goal in evaluating hematuria is to determine if it is glomerular or non-glomerular.
- Glomerular hematuria is identified by the presence of dysmorphic RBCs, RBC casts, and significant proteinuria.
- Non-glomerular hematuria is characterized by isomorphic (normal) RBCs and the absence of casts or significant proteinuria. Blood clots may be present.
- This distinction is crucial because it determines the entire subsequent diagnostic path and the specialist to whom the patient should be referred (Nephrology vs. Urology).
In our next lesson, we will continue to build on this theme of using laboratory tests to localize kidney problems. We will learn how to synthesize serum and urine markers to differentiate between prerenal, intrinsic, and postrenal acute kidney injury (AKI), another core skill in clinical medicine.