Clinical Laboratories Lab Tips
- WBC Differentials - May 2005
- Full fungal culture on CSF? - June 2005
- Drug Testing - July 2005
- Pulmonary edema after transfusion: Fluid overload or TRALI? - August 2005
- Platelet Transfusions - An Update - September 2005
- Reference laboratory tests on inpatients: Laboratory Economics 101 - October 2005
#1. WBC DIFFERENTIALS
Automated CBC's provide highly accurate counts of the red cells, white cells and platelets. They can also provide an accurate white cell differential in patients who do not have abnormal leukocytes. Unfortunately, in our patient population, that is not always the case and providing an accurate differential often requires manual review of the peripheral smear. These reviews not only increase the workload for the laboratory but can add an hour or more to the average turn-around-time for this test as compared to a CBC without a differential.
Unless there is a significant change in the WBC, an individual patient's leukocyte differential is extremely stable. Therefore, once a differential is performed, subsequent CBC's should be ordered without a differential as long as the patient's WBC remains stable. If the patient's WBC should change dramatically and you didn't order a differential, contact the laboratory and we can usually provide a differential without the need for another sample.
#2. Full fungal culture on CSF?
Fungal cultures are held for 30 days to detect slowly growing molds that primarily cause skin infections. In the past 27+ years no such organisms have been cultured from CSF at UCSF. Yeasts such as Candida albicans are extremely rare causes of meningitis and grow well on routine culture. Only two fungi are of concern as causes of meningitis, Cryptococcus neoformans and Coccidioides immitis. Culture is a relatively insensitive method to detect either of these organisms. The test of choice to diagnose Cryptococcal infection is a CSF and serum cryptococcal antigen (CRAG; available from 0800 to 2230 hours). The most sensitive test to diagnose coccidioidomycosis is an antibody test on CSF and serum. If culture for either of these fungi is desired request a cytococcal culture (box on requisition) and write in "Look for cocci."
#3. Drug Testing
The UCSF Clinical Lab offers several types of drug screens as in-house or send-out tests. Note that as there is no formal 'chain-of-custody' process for such samples the results are not useful for medical-legal purposes. The appropriate use of the various tests can be confusing and we would suggest the following guidelines be used:
A. Drugs of Abuse Screen - Rapid : This stat in-house assay with a 2-hour turn-around time detects the most commonly abused drugs and is test of choice for patients with symptoms suggestive of acute intoxication. False positives may occur with this rapid assay and if confirmation of a positive test is required it must be requested. It should not be ordered for neonates.
B. Drugs of Abuse Screen - Routine Comprehensive: This send-out assay tests for >400 compounds is primarily useful for establishing whether an individual is improperly taking drugs on a subacute or chronic basis. It takes from 10-14 days to complete the testing and is therefore not useful for the immediate clinical or social management of the patient. It should not be ordered for neonates.
C. Drugs of Abuse Screen - Routine Neonatal: Because the results of the drug screen in neonates are often a factor in the decision to discharge the infant home with the mother, any positive results of this assay are routinely confirmed by GCMS.
D. Drugs of Abuse Screen - Stat Limited :This stat send-out test is a more comprehensive screen for drugs of abuse and volatiles. Unfortunately the 6-8 hr turn-around-time makes it rarely useful in the acute setting. The treatment of most drug intoxications is empirical and supportive, and stat results are rarely needed. The Clinical Laboratories does offer in-house assays for acetaminophen, ethanol, and salicylates as well as serum osmolality for the detection of volatiles. These tests are generally sufficient for emergent patient treatment decisions.
E. Drugs of Abuse Screen - Stat Volatiles: The most frequent need for sendout drug testing is in questions of methanol or isopropanol ingestion, which this assay will detect in addition to acetone and ethanol. This assay is available with a 4-6 hr turnaround.
#4. Pulmonary edema after transfusion: Fluid overload or TRALI?
What is the No.1 mortality associated with transfusion? Transfusion-related acute lung injury or TRALI. It is new acute lung injury (ALI) that can develop immediately or within 6 hours in any patient after a transfusion of one or more blood products such as whole blood, red cells, platelets or plasma. The cause can be leukocyte antibody or bioactive substances in the donor blood. The symptoms and signs are those of ALI, i.e. acute onset of bilateral chest infiltrates, PaO2/FiO2 <300 or O2 saturation <90% on room air, and no evidence of fluid overload/cardiogenic pulmonary edema. Fever, hypotension and acute leukopenia can also occur. The incidence of TRALI is estimated to be 1:5,000 units of blood transfused and fortunately, most patients recover. Although uncommon, it is the leading cause of death associated with transfusion according to the FDA.
How do I manage the patient if I suspect TRALI? As with any transfusion reaction, stop the transfusion. TRALI patients often need intubation and mechanical ventilation. Steroids and diuretics are not useful. Order a CBC to look for acute leukopenia, and CXR to look for bilateral pulmonary infiltrates. If the patient is intubated and has fluid in the ET tube, send ET fluid and plasma for total protein to determine whether the fluid is an exudate. Look for evidence that rules out fluid overload/cardiogenic pulmonary edema e.g. cardiac history, troponin, echo, ECG, creatinine, PACWP.
Why should I report potential TRALI to the Blood Bank? When you report that your patient has potential TRALI, the Blood Bank will make sure your patient does not get another unit from the same donor. Also, implicated donors are removed from the donor pool and may prevent TRALI in another patient. Units from other donors are suitable. Therefore, call the Blood Bank 353-1313 and send all blood bags back to the Blood Bank together with a transfusion reaction form and EDTA sample.
#5. Platelet Transfusions - An Update
Platelets, administered to treat or prevent bleeding, are the most limited product available at the blood bank. Judicious detailed guidelines for their use, i.e., indications, are available on the Department of Laboratory Medicine web page under "Blood Product Information" sections "K-L" at: //latino.ucsfmedicalcenter.org/LabMan/text/4bb.html. The guidelines orient you to accepted local practice. If you have a question about an indication, we urge you to call the blood bank resident at 353-1721 for further information. Close communication will allow us to provide the best possible assistance in your patient's care.
Bacterial Testing: As part of national policy, all blood products are screened for a host of pathogens to ensure the safest possible blood supply. Beginning in 2004, platelet products began being tested for bacterial contamination. Therefore, all platelet products issued have been screened for bacterial contamination. While no test is perfect, we hope that this will further reduce the infrequent problem of transfusion-associated sepsis.
Pheresis vs. Concentrate: Platelet concentrates are obtained from a single whole blood collection, and in adults, are typically pooled into 'packs' of 6 for transfusion. Pheresis units are collected using a specialized cell separation machine that returns the red and white blood cells to the donor and leaves platelets and plasma in the collection bag. There is no good method currently available to perform bacterial testing in platelet concentrates, so all platelets issued at Moffitt-Long are pheresis units. We offer a half-pheresis unit ('pedi-pheresis') and a quarter-pheresis unit ('mini pedi-pheresis') to facilitate proper dosing for pediatric patients.
Leukoreduction: White blood cell contamination of platelet products has been associated with febrile reactions, alloimmunization, and CMV transmission. All platelet pheresis units we issue have been leukoreduced at collection, which reduces the risk of these complications and precludes the need for bedside leukoreduction in theses products. You can confirm this at the bedside by seeing a sticker on the product indicating that it has been leukoreduced.
Refractory Patients: Patients who repeatedly fail to obtain an adequate rise in their platelet count following a platelet transfusion are termed 'refractory.' The literature has linked refractoriness to, among other things, fever, splenomegaly, infection, alloimmunization, and GVHD. Should you suspect that your patient is refractory to platelet products, please call the blood bank resident (353-1721) for a consultation to begin an evaluation for obtaining crossmatched platelets. Evaluation for crossmatched platelets can be performed Monday through Friday. NOTE: Platelet counts 30-90 minutes post infusion are required to define refractoriness and therefore to qualify for crossmatch platelets.
#6. Reference laboratory tests on inpatients: Laboratory Economics 101
For outpatients, laboratory tests are billed separately from the clinic visit and other charges. Outpatient test reimbursement is either based on a pre-set price schedule (Medicare & Medi-Cal) or at some percentage discount based on our payer contracts. While the medical center typically only recovers about forty cents for each dollar it bills for laboratory tests, there is at least some reimbursement.
Most inpatient hospitalizations, on the other hand, are reimbursed a set amount based on the patient's DRG (Diagnosis Related Group) or less commonly on a per-diem basis. Under these payment systems laboratory tests are not separately billed or reimbursed. Therefore, for most hospitalized patients laboratory tests add to the cost of patient care but do not generate additional reimbursement.
Reference laboratory tests are especially significant in this regard. The charges the medical center pays 'out-of-pocket' for reference lab testing is typically significantly higher than the costs associated with performing a test in-house (this is especially true for molecular genetic tests which may cost hundreds or thousands of dollars each). Additionally, reference laboratory tests typically take much longer for the results to be returned and in many instances the patient may be discharged before the result is received. In this way, reference laboratory tests on inpatients may significantly increase the cost of care without necessarily influencing acute patient care decisions.
Our in-house test menu is relatively large and in most instances should be sufficient for patient needs during an acute inpatient stay. There are instances where a reference laboratory test is needed for inpatient care and we will send those out when requested. However, tests which are not required for acute inpatient care decisions, even if appropriate and necessary for the long term care of the patient, should be postponed until the patient has been discharged and they can be performed on an out-patient basis. In this way we can better utilize our resources without jeopardizing patient care.