Urine Kidney Tests: What's in Your Pee?
Beyond blood tests, your urine provides a direct window into the health of your kidneys and urinary tract. A Routine Urinalysis is a broad, 3-part screening test.
1. Physical (Macroscopic) Exam
The lab notes the color and clarity. Normal urine is pale yellow and clear. Cloudy urine can suggest an infection, while red or brown urine may indicate blood.
2. Chemical (Dipstick) Test
A test strip with chemical pads is dipped into the urine. This quickly checks for substances that shouldn't be there:
- Protein: Normally negative. A positive result (proteinuria) suggests kidney damage.
- Blood (Hemoglobin): Normally negative. A positive result can be from stones, infection, or glomerular disease.
- Glucose: Normally negative. A positive result (glycosuria) is a strong sign of diabetes.
- Nitrites & Leukocyte Esterase: These two together are a strong indicator of a Urinary Tract Infection (UTI).
- Ketones: Normally negative. Can be positive in diabetic ketoacidosis or starvation.
3. Microscopic Exam
The urine is spun down, and the sediment is examined under a microscope.
- Cells: Normally very few. High Red Blood Cells (RBCs) is hematuria. High White Blood Cells (WBCs) is pyuria (a sign of infection).
- Casts: These are "molds" of the kidney tubules. RBC casts are a red flag for glomerulonephritis (inflammation). WBC casts point to pyelonephritis (a kidney infection). "Muddy brown" granular casts are a classic sign of acute tubular necrosis (severe kidney injury).
- Crystals: Many are harmless, but some can indicate a risk for kidney stones (e.g., calcium oxalate or uric acid).
Urine Albumin-to-Creatinine Ratio (uACR)
This is the most important test for detecting early kidney damage, especially from diabetes and high blood pressure.
It uses a single "spot" urine sample to measure two things: albumin (a large protein that shouldn't leak out) and creatinine (a normal waste product). The ratio (uACR) corrects for how diluted your urine is.
- Normal: < 30 mg/g
- Microalbuminuria (30–300 mg/g): This is the earliest sign of kidney damage (e.g., diabetic nephropathy). It's a critical warning sign, as it appears long before your eGFR drops.
- Macroalbuminuria (>300 mg/g): This indicates more significant, established kidney disease.
Key Point: The uACR is far more sensitive than a standard dipstick. Annual uACR screening is standard for all patients with diabetes or hypertension.
24-Hour Urine Collection
This test is more cumbersome but provides a very precise measurement of *exactly* how much of a substance your kidneys excrete per day.
- Procedure: You discard your first-morning void, then collect every single drop of urine for the next 24 hours in a large jug, keeping it refrigerated.
- Why it's Used:
- To precisely quantify protein loss (e.g., to confirm nephrotic syndrome).
- For a kidney stone workup, measuring 24-hour calcium, oxalate, and uric acid levels.
Creatinine Clearance Test
This test was historically used to estimate GFR. It requires *both* a 24-hour urine collection and a blood creatinine test. However, it is cumbersome and prone to collection errors.
Key Point: This test is rarely used today. It has been almost entirely replaced by the much simpler and more reliable eGFR calculation from a blood test.