How to manage a potentially contaminated urinalysis sample?

From the Guidelines

To manage a potentially contaminated urinalysis sample, collect a new sample using proper technique, such as a clean-catch midstream collection or aseptic technique for catheterized patients, as this approach is supported by the most recent and highest quality studies 1. When collecting a new sample, it is essential to follow proper techniques to minimize contamination.

• For non-catheterized patients, instruct the patient to perform a clean-catch midstream collection by washing their hands, cleaning the genital area with antiseptic wipes from front to back, and collecting the middle portion of the urine stream in a sterile container.
• For catheterized patients, obtain the sample using aseptic technique directly from the catheter port, not the collection bag, as recommended by 1. The sample should be processed within 2 hours or refrigerated at 4°C for up to 24 hours to prevent bacterial overgrowth, as suggested by 1. It is also crucial to document any collection issues, medications, or conditions that might affect results. If contamination is suspected in the lab, such as the presence of epithelial cells, multiple organisms, or unusual findings, request a repeat sample, as proper collection technique is vital to avoid false-positive results for bacteria, white blood cells, or protein, which can lead to unnecessary treatment or missed diagnoses 1. In addition, studies have shown that the methods of specimen collection and handling are feasible in all settings and patient populations, and that midstream urine collection, with or without cleansing, is common practice for most clinical settings and patient populations 1. However, it is essential to note that the likelihood of a false positive is extremely high if a culture obtained by bag is positive, so the result must be confirmed by culturing urine obtained by a more reliable method, as stated in 1. Overall, proper collection and handling techniques are critical to ensuring accurate urinalysis results and preventing contamination.

From the Research

Distinguishing a Contaminated Sample of Urinalysis

To manage a potentially contaminated urinalysis sample, it is essential to understand the characteristics of a contaminated sample and the methods to identify them.

• A contaminated sample can lead to false-positive or false-negative results, which can affect the diagnosis and treatment of urinary tract infections (UTIs) 2.
• The presence of nitrites, leukocyte esterase, and blood in the urine can indicate a UTI, but these results must be interpreted in the context of the patient's symptoms and medical history 2, 3.
• A clean-catch technique should be used to collect midstream urine samples to minimize contamination 3.
• Urine collection bag specimens can be used for clinically stable febrile infants with suspected UTIs, but the presence of leukocyte esterase or nitrites warrants more invasive urine collection 3.

Characteristics of a Contaminated Sample

• The presence of epithelial cells, bacteria, or other contaminants in the urine can indicate a contaminated sample 4.
• A urine sample with a high specific gravity or an abnormal pH level can also suggest contamination 3.
• The presence of bilirubin, urobilinogen, or other substances in the urine can indicate underlying medical conditions, but these results must be interpreted in the context of the patient's symptoms and medical history 3.

Methods to Identify Contamination

• Microscopic examination of the urine can help identify contaminants such as epithelial cells, bacteria, or other substances 4, 3.
• Dipstick testing can also help identify contaminants, but the results must be interpreted in the context of the patient's symptoms and medical history 2, 3.
• Urine culture is the gold standard for detecting UTIs, but it can also help identify contaminants in the urine sample 2.