Before undergoing surgery, it is common for doctors to order a urine test. This pre-operative urine test serves several important purposes and can provide valuable information to help ensure a safe and successful procedure.
Looking for signs of infection
One of the main reasons to test a patient’s urine before surgery is to check for any signs of infection. The urinary tract is a common site of infection, especially for those undergoing urologic or gynecologic procedures. An undiagnosed urinary tract infection (UTI) can spread during surgery and lead to more serious complications. The pre-op urine test allows doctors to detect and treat any infections beforehand.
Doctors will look for the presence of bacteria, white blood cells, and other signs of inflammation that point to infection. Common techniques include a simple dipstick test, a urine culture, or a urinalysis under a microscope. Finding infection early on helps prevent sepsis and allows antibiotics to clear the infection prior to surgery.
Assessing kidney function
The preoperative urine test also provides important information about how well the kidneys are working. Doctors can get clues about kidney function and hydration status from the color, concentration, and chemical composition of urine.
Dark or concentrated urine may indicate dehydration or kidney problems. The presence of protein, blood, glucose, and waste products in abnormal amounts can signal issues like urinary tract obstruction, chronic kidney disease, or diabetic nephropathy. Knowing if the kidneys are impaired allows the surgical team to plan accordingly and provide appropriate perioperative care.
Checking for pregnancy
For premenopausal women undergoing surgery, a urine pregnancy test is typically standard protocol. Surgery under anesthesia can pose risks to unborn fetuses. The urine hCG test can reliably determine if a woman is pregnant before proceeding with an elective operation.
Some medications and treatments given around the time of surgery may also be harmful in pregnancy. A negative pregnancy test provides reassurance and allows surgery to be performed safely.
Looking for traces of drugs or toxins
Illicit drugs, prescription medications, herbs, and other chemical substances can remain in the body for a period of time and be detected in urine. A pre-op urine toxicology screen helps identify any potentially interacting or contraindicated agents the patient may have used recently.
Substances like cocaine, marijuana, amphetamines, opioids, and certain supplements can have implications for anesthesia, surgery, and recovery. This allows the medical team to avoid complications and adverse reactions by making appropriate modifications to the surgical and medication plan.
Testing urine allows for early intervention
In summary, preoperative urine testing provides a simple, non-invasive way for doctors to get valuable information about a patient’s health status before undertaking the risks of surgery. Checking for infection, kidney function, pregnancy status, and recent drug use allows the medical team to identify issues and take appropriate precautions well in advance of the procedure.
Catching problems early on helps prevent complications both during and after surgery. Addressing potential issues ahead of time leads to better outcomes. The urine pre-op tests cue doctors into take actions like delaying surgery, initiating antibiotics, adjusting anesthesia, or providing additional perioperative care as needed.
While the specific components of the pre-surgical urine test may vary, most will include a dipstick urinalysis looking at:
- Color and clarity – Dark or cloudy urine can indicate dehydration, infection, kidney disease, or other abnormalities.
- Leukocyte esterase – An enzyme from white blood cells, indicates inflammation/infection.
- Nitrites – A byproduct of bacteria, signalling a UTI.
- Protein – Excess protein in urine may point to kidney dysfunction.
- Glucose – High levels can be a sign of diabetes.
- Ketones – Can occur with high blood glucose or starvation.
- Bilirubin – Indicates liver problems or blocked bile ducts when elevated.
- Blood – May be seen with UTI, kidney disease, menstruation, or trauma.
- pH – Abnormal urine acidity/alkalinity can reflect diet, illness, or metabolism.
- Specific gravity – Concentration helps assess hydration status.
Additional urine testing tools commonly used before surgery include:
- Urine culture – Growing bacteria from a urine sample identifies organisms and sensitivities.
- Microscopic urinalysis – Detects cells, crystals, casts, and bacteria under the microscope.
- Pregnancy test – Urine hCG assay determines pregnancy status.
- Toxicology screen – Checks for presence of therapeutic or illicit drugs.
Reasons for abnormal pre-op urine test results
While a normal preoperative urine test is reassuring, abnormal results warrant further evaluation to determine underlying causes. Here are some reasons for unusual urine findings before surgery:
Infection
- UTI
- Pyelonephritis – Kidney infection
- Glomerulonephritis – Inflamed glomeruli
- Prostatitis – Prostate gland infection
- Cystitis – Bladder infection
- Urethritis – Urethra infection
Kidney dysfunction
- Acute kidney injury
- Chronic kidney disease
- Glomerular disorders like nephritic syndrome
- Bladder obstruction
- Renal calculi – Kidney stones
- Interstitial nephritis – Kidney tubule inflammation
- Diabetic nephropathy
- Hydronephrosis – Kidney swelling from urine backup
Endocrine/metabolic conditions
- Uncontrolled diabetes leading to glucosuria and ketoacidosis
- Cushing’s syndrome
- Hyperthyroidism
- SIADH – Inappropriate antidiuretic hormone secretion
- Addison’s disease – Adrenal insufficiency
Other systemic disease
- Liver failure with bilirubinuria
- Multiple myeloma
- Sickle cell disease
- Urinary tract cancers like bladder cancer or renal cell carcinoma
- Interstitial cystitis – Bladder wall inflammation
- Nephrotic syndrome
- Lupus nephritis
Pharmacologic causes
- Medications like NSAIDs, chemotherapy, laxatives, diuretics
- Herbals or supplements
- Illicit substances
Other factors
- Pregnancy
- Heavy exercise
- Dehydration
- Recent urologic procedures
- Menstruation
- Trauma
- Prolonged immobilization
Preoperative urine testing process
Here is a typical workflow for pre-operative urine testing:
- Patient is scheduled for surgery and instructed to provide a fresh urine sample shortly before the procedure date.
- Sample is collected at home, at the surgeon’s office, or at the hospital prior to admission.
- Basic dipstick urinalysis is performed by nurses at point-of-care.
- Urine specimen is sent to lab for additional testing like culture, microscopy, pregnancy test, and/or toxicology screen per physician orders.
- Results are reported to the surgical care team and incorporated into the overall medical assessment.
- For any positive findings, additional actions are taken such as initiating antibiotics for UTI, postponing elective surgery, opting for spinal vs general anesthesia, modifying drug regimens to avoid interactions, or providing extra hydration/monitoring intraoperatively.
- The benefits of early detection from pre-op urine testing support safety and optimal surgical outcomes.
Conclusion
Preoperative urine testing provides a quick, noninvasive way to screen for medical conditions that could impact surgical risk and outcomes. Checking for signs of infection, kidney function, pregnancy status, and drug use enables early detection and intervention when abnormalities are found.
Catching issues ahead of time allows doctors to delay surgery if needed, start antibiotics, adjust anesthesia type, prescribe protective medications, opt for less invasive procedures, provide enhanced monitoring intraoperatively, and take other actions to mitigate complications. Being well-informed about the patient’s health before undertaking anesthesia and surgery supports the best possible experience and recovery.
