🧫 Lab Values & Diagnostics Lesson

CGPBKN: six key urinalysis findings

A simple urine sample can reveal diabetes, kidney disease, infection, and more — six findings, each pointing toward a different diagnosis.

Color

Glucose

Protein

Blood

Ketones

Nitrites

📖 Full Breakdown

Six urinalysis findings and what each abnormal result suggests

Normal urine is clear, pale yellow, with a pH between 4.5–8 and specific gravity between 1.001–1.035 — deviations from this baseline point in specific diagnostic directions.

Glucose (Glucosuria)

Blood glucose exceeded 180 mg/dL

This threshold is called the renal threshold — once blood glucose exceeds it, the kidneys can no longer reabsorb all the filtered glucose, and it spills into urine. Classic finding in diabetes.

Protein (Proteinuria)

Kidney disease indicator

Suggests kidney disease broadly, with nephrotic syndrome (protein >3.5 g/day plus edema and low albumin) representing a more severe, specific presentation.

Blood (Hematuria)

Never a normal finding

Suggests UTI, kidney stones, or cancer — always warrants further investigation regardless of how minor it initially appears.

Ketones

Fat metabolism byproduct

Appears during starvation, diabetic ketoacidosis (DKA), or a low-carbohydrate diet — the body is burning fat for fuel instead of glucose.

Nitrites

A specific bacterial signature

Gram-negative bacteria convert nitrates (normally present in urine) into nitrites — a positive nitrite result is a strong, specific indicator of bacterial UTI, most commonly E. coli.

Casts

Where in the kidney the problem is

RBC casts specifically indicate glomerulonephritis (red blood cells squeezed through damaged glomeruli); WBC casts indicate pyelonephritis (kidney infection) — the type of cast pinpoints the location and nature of kidney pathology.

🩺 Clinical / Exam Application

A patient with UTI symptoms has a urinalysis showing positive nitrites and elevated WBCs. Because nitrites specifically result from gram-negative bacteria converting nitrates in the urine — a chemical signature that essentially can't happen without bacterial presence — this combination essentially confirms a bacterial UTI (most likely E. coli) before urine culture results are even back, allowing a clinician to start empiric antibiotics immediately.

⚠️ Exam Alert

RBC casts vs. WBC casts is a frequently tested pairing: RBC casts are considered pathognomonic (uniquely diagnostic) for glomerulonephritis, while WBC casts point to pyelonephritis — exam questions often test whether you can match the specific cast type to its corresponding kidney pathology.

🚧 Common Trap

Don't assume glucose in the urine always means diabetes. While it's the classic cause, glucosuria can also occur in pregnancy due to normal physiologic changes in kidney filtration — context matters when interpreting this finding.

✅ Quick Check

A urinalysis shows RBC casts. What specific kidney condition does this finding point toward, and how does that differ from what WBC casts would suggest?

📝 Exam Prep

Common Exam Questions

❓ What does a positive nitrite result on urinalysis indicate?

✅ A positive nitrite result indicates bacterial infection — gram-negative bacteria (most commonly E. coli) convert nitrates naturally present in urine into nitrites, making this a fairly specific marker for UTI.

❓ What is the difference between RBC casts and WBC casts in urine?

✅ RBC casts are pathognomonic for glomerulonephritis, formed when red blood cells are squeezed through damaged glomeruli. WBC casts indicate pyelonephritis (kidney infection).