Urinalysis and Urine Culture - Diagnostic Evaluation

Diagnostic Evaluation

URINALYSIS AND URINE CULTURE

The urinalysis provides important clinical information on kidney function and helps diagnose other diseases, such as diabetes. The urine culture determines if bacteria are present in the urine, as well as their strains and concentration. Urine culture and sensi-tivity also identify the antimicrobial therapy that is best suited for the particular strains identified, taking into consideration the an-tibiotics that have the best rate of resolution in that particular geo-graphic region. Appropriate evaluation of any abnormality can assist in detecting serious underlying diseases.

Urine examination includes the following:

·      Urine color (Table 43-3)

·       Urine clarity and odor

·       Urine pH and specific gravity

·       Tests to detect protein, glucose, and ketone bodies in the urine (proteinuria, glycosuria, and ketonuria, respectively)

·      Microscopic examination of the urine sediment after cen-trifuging to detect RBCs (hematuria), white blood cells, casts (cylindruria), crystals (crystalluria), pus (pyuria), and bacteria (bacteriuria)

Significance of Findings

Several abnormalities, such as hematuria and proteinuria, pro-duce no symptoms but may be detected during a routine urinal-ysis using a dipstick. Normally, about 1 million RBCs pass into the urine daily, which is equivalent to one to three RBCs per high-power field. Hematuria (more than three RBCs per high-power field) can develop from an abnormality anywhere along the genitourinary tract. Common causes include acute infection (cys-titis, urethritis, or prostatitis), renal calculi, and neoplasm. Other causes include systemic disorders, such as bleeding disorders; ma-lignant lesions; and medications, such as warfarin (Coumadin) and heparin. Although hematuria may initially be detected using a dipstick test, further microscopic evaluation is necessary (Na-tional Institute of Diabetes & Digestive & Kidney Diseases [NIDDK], 1999).

Protein in the urine (proteinuria) may be a benign finding, or it may signify serious disease. Occasional loss of up to 150 mg/day of protein in the urine, primarily albumin and Tamm-Horsfall protein, is considered normal and usually does not require further evaluation. A dipstick examination, which can detect from 30 to 1,000 mg/dL of protein, should be used as a screening test only, because urine concentration, pH, hematuria, and radiocontrast materials all affect the results. Because dipstick analysis does not detect protein concentrations of less than 30 mg/dL, the test can-not be used for early detection of diabetic nephropathy. Micro-albuminuria (excretion of 20 to 200 mg/dL of protein in the urine) is an early sign of diabetic nephropathy. Common benign causes of transient proteinuria are fever, strenuous exercise, and prolonged standing.

Causes of persistent proteinuria include glomerular diseases, malignancies, collagen diseases, diabetes mellitus, preeclampsia, hypothyroidism, heart failure, exposure to heavy metals, and use of medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs) and angiotensin-converting enzyme inhibitors (NIDDK, 2000).