Evaluation of a filter system to harvest plasma for identification of failure of passive transfer in newborn calves.

The objective of this study was to evaluate a filter system to harvest plasma to assess failure of passive transfer (FPT) in newborn calves. Blood samples (n = 227) for serum and plasma harvesting were collected via jugular vein puncture from Holstein calves aged 1 to 7 d from 4 commercial dairy herds in Northeast Germany. Serum IgG concentrations were determined using a sandwich ELISA. Failure of passive transfer was defined as IgG concentrations <10 mg/mL and used as a gold standard. One handheld optical refractometer (Euromex Holland, Arnhem, the Netherlands) and 2 digital Brix refractometers (device 1: HI 96801 digital refractometer, Hanna Instruments, Woonsocket, RI; device 2: Misco PA201, Misco, Solon, OH) were used to analyze total proteins in serum or plasma. The colostrum uptake of the calf can thus be monitored and calves with FPT can be identified. Serum was obtained through centrifugation. Plasma was obtained through either a filter system or centrifugation. For plasma filtration, approximately 2 mL of lithium heparin blood was injected into the inlet reservoir of a plasma filter (2-Drop-Filter, Pharmadoc, Lübeck, Germany) using a disposable syringe. Receiver operating characteristic curve analyses were used to determine optimum thresholds for each of the 3 devices using different media. Sixty-seven (30%) calves had FPT. For the handheld optical refractometer, the optimum threshold was 5.6 g/dL [sensitivity 70.1%; specificity 80.0%; positive predictive value (PPV) 60.1%; negative predictive value (NPV) 86.2%; area under the curve (AUC) 0.85] using serum. For centrifuged plasma, the optimum threshold was 6.3 g/dL (sensitivity 82.1%; specificity 68.1%; PPV 52.5%; NPV 89.9%; AUC 0.84), and for filtered plasma, the threshold was 6.0 g/dL (sensitivity 56.7%; specificity 90.0%; PPV 70.9%; NPV 82.9%; AUC 0.80). For device 1, the optimum threshold was 8.9% Brix (sensitivity 82.1%; specificity 63.8%; PPV 48.7%; NPV 89.5%; AUC 0.81), 9.4% Brix (sensitivity 76.1%; specificity 73.7%; PPV 55.4%; NPV 87.8%; AUC 0.80), using serum and centrifuged plasma, respectively. For device 2, the optimum threshold was 8.7% Brix (sensitivity 74.6%; specificity 76.2%; PPV 57.4%; NPV 87.5%; AUC 0.83), 9.5% Brix (sensitivity 80.6%; specificity 70.6%; PPV 54.0%; NPV 89.5%; AUC 0.83), and 9.2% Brix (sensitivity 58.2%; specificity 87.5%; PPV 66.6%; NPV 83.0%; AUC 0.80) using serum, centrifuged plasma, and filtered plasma, respectively. Based on the AUC, the 3 devices yielded comparable test characteristics to identify calves with FPT. In conclusion, a filter system can be used to facilitate the evaluation of FPT as a point of care technique in calves without the need for serum centrifugation.