# Situation: A 76-year-old woman is brought to the clinic by her daughter because for 2 days she has been more confused than usual and has been wetting herself several times a day. She walks without help, can follow simple instructions, and has no fever. She takes no regular medicines. A urine dipstick is positive for nitrite and leukocyte esterase, and the physician orders a urine culture. The clean-catch midstream specimen is collected, but it cannot reach the laboratory for 3 hours. What should the nurse do with it?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=629714  
> language: ko  
> subject: Nursing Practice III — Care of Clients with Problems in Surgery, Oxygenation, Fluid and Electrolytes, Infectious, Inflammatory and Immunologic Response, Cellular Aberrations

## 문제

Situation: A 76-year-old woman is brought to the clinic by her daughter because for 2 days she has been more confused than usual and has been wetting herself several times a day. She walks without help, can follow simple instructions, and has no fever. She takes no regular medicines.

A urine dipstick is positive for nitrite and leukocyte esterase, and the physician orders a urine culture. The clean-catch midstream specimen is collected, but it cannot reach the laboratory for 3 hours. What should the nurse do with it?

## 보기

1. Add a preservative tablet from the dipstick kit
2. Keep it at room temperature in the clinic
3. Refrigerate it until it can be sent **✔ 정답**
4. Discard it and collect a new specimen later

**정답: 3**

## 해설

A urine culture specimen should reach the laboratory promptly; if transport will be delayed, it is refrigerated according to laboratory policy. At room temperature, the bacteria in the sample keep multiplying, so a contaminated or low-count specimen can falsely appear to meet the culture threshold. The specimen is labeled and sent as soon as transport is available.

## 심화 해설

Why refrigeration is the correct action

A urine culture is not like a routine urinalysis. The goal is to identify and quantify the bacteria that were actually present in the bladder at the time of collection. Once urine leaves the body, any bacteria in the specimen continue to divide as long as the temperature and nutrients allow. A delay of 3 hours at room temperature is enough time for a small number of contaminants to multiply into a colony count that falsely meets the threshold for a urinary tract infection [1][3]. Refrigerating the specimen at 4°C slows bacterial metabolism and preserves the bacterial count close to what it was when the sample was collected [1][2].

The preanalytic phase—collection, preservation, storage, and transport—is the most important controllable factor in urine culture accuracy. Errors here cannot be corrected later in the laboratory, and they directly affect whether the patient is diagnosed and treated appropriately [2].

| Storage condition | Effect on bacterial count | Risk for culture result |
| --- | --- | --- |
| Room temperature for several hours | Bacteria continue multiplying | False-positive or falsely high colony count from contaminants |
| Refrigerated at 4°C | Bacterial growth markedly slowed | Preserves the original bacterial load until plating |
| Chemical preservative such as boric acid | Inhibits bacterial overgrowth | Useful when refrigeration is unavailable, but requires the correct preservative tube and fill volume |

Watch out! The dipstick kit preservative tablet is not interchangeable with a urine culture preservative. Dipstick preservatives are designed to stabilize chemical analytes, not to maintain quantitative bacterial counts for culture. Adding the wrong tablet can interfere with culture results.

Key point! The specimen should be labeled and sent as soon as transport is available. Refrigeration is a temporary holding measure, not a substitute for prompt delivery to the laboratory.

In this patient, the positive nitrite and leukocyte esterase suggest a true urinary tract infection, but the culture must reflect the actual bladder flora. Keeping the specimen at room temperature could allow a low-count contaminant to overgrow and obscure the true pathogen, or it could falsely elevate the count of an organism that was not clinically significant [3]. Boric acid preservative tubes are an evidence-based alternative when transport delays are unavoidable, but they require the correct tube type and adequate urine volume to maintain the proper preservative concentration . In a clinic setting where refrigeration is available, cold storage is the simplest and most reliable intervention [1][2].References (research sources)

- [1]Evaluation of the BD Vacutainer Plus Urine C&S Preservative Tubes compared with nonpreservative urine samples stored at 4°C and room temperature.Research articleEisinger SW, Schwartz M, Dam L, Riedel S (2013) · DOI: 10.1309/AJCP5ON9JHXVNQOD

- [2]Effectiveness of Preanalytic Practices on Contamination and Diagnostic Accuracy of Urine Cultures: a Laboratory Medicine Best Practices Systematic Review and Meta-analysis.Meta-analysis/systematic reviewLaRocco MT, Franek J, Leibach EK, Weissfeld AS, Kraft CS, Sautter RL (2016) · DOI: 10.1128/CMR.00030-15

- [3]Evaluation of liquid and lyophilized preservatives for urine culture.Research articleWeinstein MP (1983) · DOI: 10.1128/jcm.18.4.912-916.1983

## 임상 시나리오

Urine Culture TransportPreventing false-positive results from delayed processing
If a urine culture cannot reach the laboratory within 2 hours, refrigerate it at 4°C immediately. Refrigeration slows bacterial metabolism and preserves the original colony count until plating.

At room temperature, contaminating bacteria multiply rapidly. A delay of 3 hours can turn a low-count contaminant into a colony count that falsely meets the threshold for urinary tract infection.

CautionA dipstick preservative tablet is not a substitute for culture transport media. If refrigeration is unavailable, use a boric acid preservative tube with the correct fill volume, and label the specimen before sending.

## 핵심 개념

- **Preanalytic phase** — All steps before laboratory analysis, including collection, storage, and transport, which determine specimen accuracy.
- **Clean-catch midstream** — A collection method that reduces contamination by discarding initial urine flow and collecting the middle portion.
- **Colony count** — The number of bacterial colonies grown per milliliter of urine, used to define significant bacteriuria.
- **Boric acid preservative** — A chemical additive that inhibits bacterial overgrowth when refrigeration is unavailable, requiring correct tube fill volume.
- **False-positive culture** — A result that incorrectly indicates infection due to contaminant multiplication during delayed transport at room temperature.

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