Laboratory Testing Flashcards
What is the purpose of Peritoneal Equilibration Test (PET)?
Used to assess the transport characteristics of the peritoneal membrane for each individual patient.
This test uses a series of dialysate and blood samples to measure solute equilibration, rate of glucose absorption and net ultrafiltration.
Samples of Peritoneal Dialysis Fluid (PDF) are collected at 0, 2, and 4-hour intervals and sent to the lab for urea, creatinine and glucose. Serum for urea, creatinine and glucose is drawn at the 2-hour mark.
Prior to the PET test a 2.5% or 4.25% dextrose dialysate is infused allowing for a 10-12 hour overnight dwell.
For the 24-hour batch collection, the overnight dwell and the first void of the day are discarded. The collection starts with the next void, using a urine collection container. The collection continues for exactly 24-hours, saving all urine and drained effluent from each exchange. An aliquot sample is drawn from each exchange, the samples are mixed and a 10ml sample of combined effluent is sent to the lab for urea and creatinine. The sample should be refrigerated if it cannot be immediately sent. A blood sample is also drawn for urea/creatinine.
What is the purpose of taking a “Culture”?
To Measure the growth of microorganisms or living tissue cells in a special media.
Organisms that grow are then identified and tested for sensitivity to various antibiotics.
The length of time needed to produce a positive culture varies.
Final results often take 3-5 days.
Why is it important to obtain peritoneal cultures?
It is sometimes possible to determine why and how a patient got infected based on the culture report.
Organisms enter the peritoneum in various ways. Intra-luminal infections travel to the peritoneum via the catheter.
Touch contamination or damaged PD systems are two examples of this method of entry.
Bacteria entering the peritoneum via the peritoneal tract (or tunnel) are called peri-luminal.
An example of this is an exit site infection.
Transmural infections enter the peritoneum through the bowel wall and hematogenous infections come from the bloodstream. In females, organisms can travel through the reproductive tract.
Identifying the portal of entry can be useful in determining the most appropriate treatment for the patient and hopefully to prevent recurrence.
How are exit site cultures obtained?
Normal skin flora will produce a positive culture. Always swab the exudates (drainage), not the dry skin.
The patient should not perform exit site care prior to coming to the clinic so that the exudates are not washed away.
Be sure to culture the site prior to treatment with any cream, ointment or other agent.
What needs to be considered for taking PD effluent cultures?
A higher concentration of organisms in the effluent reduces the chance of a “no growth” result.
An effluent sample that had been dwelling in the peritoneum at least four hours should be cultured if available.
Before obtaining the specimen, be sure to mix the drain bag well and disinfect the sample port to avoid contaminating the sample.
Aerobic and anaerobic culture samples will be sent to the lab (green and purple bottles).
Collect a conical yellow top tube for gram stain testing which is included in ordering peritoneal dialysis fluid (PDF) cultures.
What is gram staining?
A procedure used to classify bacteria into one of two groups known as gram positive and gram negative.
Results can be obtained in one hour and can be used to determine which class of antibiotics would be effective for initial treatment.
What is acid-fast staining?
A laboratory test taken from a body fluid sample used to identify organisms of the genus mycobacterium, which cannot be detected by gram stain.
What is a cell count with differential?
Laboratory test ordered when peritonitis is suspected.
Collect effluent PD sample in a lilac tube and label it as PDF (peritoneal dialysis fluid).
PD effluent should be essentially free of cells.
In this type of test, cells are counted and identified by cell type.
The percentage of cell types is compared to the total number of white blood cells present.
A cell count greater than 100 WBC with 50% or more neutrophils suggests peritonitis.
It is important to include a “differential” in the cell count as there are times when a patient may have a high cell count causing the fluid to be cloudy.
The cloudiness is from an increase in the number of monocytes or eosinophils.
Most of these cases do not require antibiotics, but may require an alternative treatment.
