Evaluation of serum and rapid serum separator collection tubes for therapeutic drug assays.

Appropriate specimen collection and storage is essential to preserve sample integrity and ensure accurate test results. The default collection containers for blood drug concentrations are tubes without gel separators to avoid possible drug adsorption. However, routine chemistry tests are generally collected in gel separator tubes due to their convenient transport and processing; collection of an additional gel-free tube is often required for drug measurements. Citrated whole blood was pooled, spiked with drug, and transferred to three tubes (red, SST gold, RST orange) containing calcium chloride. Blood was allowed to clot, centrifuged and stored at ambient temperature (24 h) or refrigerated (7 days). At defined times, serum drug concentrations were determined (Roche cobas c502). Based on these results, specimen collection requirements were updated to allow serum separator tubes for 17 assays. Of the 21 assays evaluated, 18 displayed acceptable stability in both gel-containing tubes (acetaminophen, amikacin, carbamazepine, digoxin, ethanol, gentamicin, lamotrigine, levetiracetam, lithium, methotrexate, phenobarbital, phenytoin, salicylate, theophylline, tobramycin, valproic acid, vancomycin, voriconazole). Three drugs displayed strong decreases in measured concentrations after storage in one or both gel-containing tubes (total tricyclics, lidocaine, and free phenytoin). Following adoption of gel-containing tubes, 94% of the five most frequently ordered drug monitoring tests in the Emergency Department were collected in serum separator tubes. Evaluation of the stability and accuracy of commonly monitored drugs revealed that the majority were not affected by exposure to gel separator material under conditions similar to outpatient clinic storage, courier transport, and laboratory storage. Expanding the collection requirements for appropriate drugs to include gel separator tubes decreases the number of specimens drawn and the complexity of laboratory workflows.

Origin of a false positive urine pregnancy test in a patient with membranoproliferative glomerulonephritis type I.

BACKGROUND: Discrepant qualitative urine and quantitative serum hCG results were observed in a patient with a history of membranoproliferative glomerulonephritis. Further studies were performed to investigate this discrepancy. METHODS: Urine and serum specimens were analyzed using alternate methods and heterophilic antibody blocking and dilution studies were performed. The potentially interfering substance was identified and subsequent specimens from the patient's hospital stay were analyzed for hCG and the effect of the interferent was assessed. RESULTS: Initially, the patient's urine specimen was positive for the presence of hCG based on the qualitative QuickVue+hCG point-of-care device. However, quantitative serum testing was negative for pregnancy on the Tosoh AIA-1800 analyzer (<2 mIU/ml). The serum specimen was also positive on the QuickVue+device, but upon incubating urine or diluted serum with heterophilic antibody binding reagent, hCG results shifted from positive to negative. Although the patient had a non-elevated human anti-mouse antibody (HAMA) level, the patient exhibited an elevated serum rheumatoid factor concentration (270 IU/ml; reference interval: ≤20 IU/ml). Application of a calibrator solution containing rheumatoid factor at levels above 175 IU/ml resulted in a positive reading on the QuickVue+point-of-care card. CONCLUSION: The discrepancy between the qualitative urine and quantitative hCG results was due to an interfering substance causing a false positive on the QuickVue+urine point-of-care device. Subsequent studies identified rheumatoid factor as the potential interferent in this case.

Retroperitoneal masses with associated human chorionic gonadotropin production: Report of two cases.

BACKGROUND: The production of human chorionic gonadotropin (hCG) can be stimulated by both pregnancy and malignancy. METHODS: Two patients with increased serum hCG and a retroperitoneal mass were monitored throughout the course of disease to evaluate fluctuations in hCG concentrations. Pathologic examination was performed on the resection specimens. RESULTS: The retroperitoneal masses were identified as a benign epidermoid cyst and pancreatic ductal adenocarcinoma. The serum hCG concentration of the patient with the splenic epidermiod cyst decreased upon resection of the mass, and immunohistochemical staining demonstrated that the cyst lining expressed hCG. This is the first report of hCG secretion by an epidermoid cyst. The serum hCG concentrations of the patient with pancreatic adenocarcinoma paralleled the secretion of cancer antigen 19-9 and reflected the course of disease progression. Additional testing suggested that a different form of hCG was produced by each neoplasm. CONCLUSIONS: hCG secretion may be associated with both benign and malignant neoplasms. Laboratory testing can be utilized to further characterize increased serum hCG, and may help to determine the etiology of the increased hCG.