Lab Tests Reference Library

Urine pH measures the acidity or alkalinity of urine on a scale of 4.5 to 8.5. The kidneys are the primary regulators of body acid-base balance, and urine pH reflects the net acid or alkali excreted. Urine pH is assessed on dipstick urinalysis and is useful for evaluating kidney stone risk, acid-base disorders, and urinary tract infections.

Urine dipstick protein detects protein (primarily albumin) in the urine. The healthy kidney filters blood through glomeruli that prevent large proteins from passing into urine. Protein in urine (proteinuria) indicates glomerular damage, tubular dysfunction, or overflow proteinuria. It is one of the most important markers for kidney disease and a major risk factor for both kidney disease progression and cardiovascular disease.

Urine glucose (glucosuria) occurs when blood glucose exceeds the renal threshold — approximately 180 mg/dL (10 mmol/L) — at which the kidney tubules can no longer reabsorb all filtered glucose. Glucose spills into the urine. Urine glucose is a screening finding that almost always indicates either uncontrolled diabetes or renal glycosuria (a benign tubular defect where glucose leaks at normal blood sugar levels).

Urine ketones (ketonuria) indicates that the body is breaking down fat as its primary energy source instead of glucose — producing ketone bodies (acetoacetate, beta-hydroxybutyrate, acetone). Ketones detected in urine by dipstick (primarily acetoacetate) signal a state of inadequate glucose utilization. In a diabetic patient with positive urine glucose, ketonuria is a warning sign of impending diabetic ketoacidosis (DKA) — a life-threatening emergency.

Hematuria (blood in urine) can be gross (visible to the naked eye — pink, red, or brown urine) or microscopic (visible only on dipstick or microscopy). The urine blood dipstick detects hemoglobin and myoglobin through a peroxidase reaction. Any unexplained hematuria — especially in adults over 35 — requires thorough evaluation to exclude urinary tract malignancy, even if the cause appears benign.

Urine nitrites are produced by bacterial reduction of dietary nitrates to nitrites — a metabolic activity of most Gram-negative bacteria (E. coli, Klebsiella, Proteus, Enterobacter). A positive urine nitrite on dipstick indicates the presence of bacteria that can perform this conversion and strongly suggests urinary tract infection. When positive nitrites are combined with positive leukocytes (white blood cells), the specificity for UTI approaches 95%.

White blood cells (leukocytes) in urine — called pyuria — indicate inflammation or infection within the urinary tract. Leukocytes are detected on dipstick by leukocyte esterase (an enzyme released by neutrophils) and quantified on microscopy as WBC per high-power field. More than 5 WBCs per high-power field (WBC/HPF) on microscopy is the accepted threshold for significant pyuria.

The Albumin-to-Creatinine Ratio (ACR), measured on a spot (random) urine sample, is the preferred test for detecting and quantifying urine albumin excretion in clinical practice. By dividing albumin by creatinine (both in the same sample), ACR corrects for urine dilution — providing a reliable estimate of 24-hour albumin excretion without the inconvenience and inaccuracy of a 24-hour urine collection.

Urine specific gravity (USG) measures the concentration of solutes in urine relative to pure water (specific gravity 1.000). A higher specific gravity indicates more concentrated urine (more solutes); a lower value indicates more dilute urine. USG reflects the kidney's ability to concentrate and dilute urine — one of the most fundamental tests of tubular and kidney function. It is measured as part of routine urinalysis by refractometer or dipstick.

24-hour urine protein quantifies the total amount of protein excreted in urine over an entire day. It is the traditional gold standard for diagnosing nephrotic syndrome and precisely quantifying proteinuria for staging and monitoring kidney disease. The test eliminates the inaccuracy of single-time-point measurements by capturing the full diurnal variation in protein excretion.