Editor’s note: This month, Sandra L. Honigfort, BSMT(ASCP), returns as our clinical expert, answering questions from three readers. Sandra is Laboratory Services Coordinator and Infection Prevention Coordinator at Paul Oliver Memorial Hospital in Frankfort, MI.
Q At our lab we have been receiving four tubes on CSF samples. The physicians request counts on tubes 1 and 4. Doing that changes the order in which the tubes for microbiology and chemistry are used. Currently, textbooks state to use tube 1 for chemistry, 2 for microbiology, and 3 for hematology. Since both tubes 1 and 4 are in hematology, what would be the best for tubes 2 and 3? Can you also supply adequate documentation of your findings so we can have a sufficient record for CAP?
A The original texts based the CSF samples on the practice of obtaining three tubes and so chose the last tube (#3) for the cell count. This was to negate any trauma associated with the tap as much as possible. Current practice of using four tubes would use this logic to specify tube #4 for the count. The practice of using tubes #1 and #4 for counts has become fairly common, as this aids the clinician in determining if the cells come from a traumatic tap or are actually a problem with the CSF.
Microbiology was designated on the #2 tube with the idea that if there were skin flora it would dilute out. Using this same logic, it would make sense to use the #3 tube for micro and the #2 for chemistries. Unfortunately in my literature search I could not find any text references stating this explicitly. There are a few anecdotal articles that describe the practice at various facilities that can be found by doing a Google Scholar search. Until we have a formal study of these practices, there will most likely not be a change in the textbook methods.
Q In my laboratory I measure Calcium in mmol/L, Total Protein in g/L and Albumin in g/L. What is the formula for calculating the Ionized Calcium?
A There are a number of different equations used to calculate ionized calcium, ranging from simple to quite complex. Here are several:
- Total calcium – (Total protein x 0.8)
This assumes albumin and globulin concentrations are not unusual! - Total calcium – 0.707 x (albumin – 3.4) = corrected calcium
This is a typical equation for calculating corrected total calcium using total calcium (mg/dL) and albumin (g/dL). - Total calcium / (0.6 + 0.05 x total protein) = corrected calcium
This is another typical equation for calculating corrected total calcium from total calcium (mg/dL) and total protein (g/dL). - 0.25 x [0.9 + (0.55 x total calcium) – (0.3 x albumin)] = ionized calcium
This equation calculates ionized calcium (mmol/L) from total calcium (mg/dL) and albumin (g/dL). - Total calcium – (0.00613 x total calcium x albumin) – (0.00244 x total calcium x globulin) – (0.0043 x total calcium x AG) – (0.00375 x total calcium x HCO3) = ionized calcium
This equation calculates ionized calcium (mmol/L) from six measurements: total calcium (mmol/L); albumin (g/L); globulin (total protein – albumin; g/L); anion gap (AG; mmol/L); and bicarbonate (HCO3; mmol/L).
The question is, which one to use? There are pros and cons to each of the equations, and the real decision is whether to use a calculation or actually do a direct measure of ionized calcium. Many of today’s chemistry analyzers are capable of measuring ionized calcium. This is becoming the standard as calculated results are being phased out.
Q If a patient is transferred by ambulance with a unit of blood infusing, does an RN have to ride with him or her or can a paramedic do so? Also, if a suspected transfusion reaction occurs after the patient reaches the other facility, who is responsible for the workup?
A The AABB technical manual states only that a “qualified” person must be present while blood is infusing. It is up to each medical director to make the decision as to whom they consider “qualified.” In reviewing policies from several healthcare organizations, I have found references for both paramedics and RNs. In either case, the person will need to have been trained in transfusion policies and follow the written protocols for transfusion.
There is no cut-and-dried approach to who is responsible for the transfusion reaction workup. The transferring and receiving facilities should come to an agreement about how these will be handled. Since the original specimens will be at the transferring facility and the post specimens will be at the receiving facility, they will need either to courier specimens or share the workup with each facility doing the testing on the specimens in their possession. If a true transfusion reaction time is of concern, it might be more expedient for each facility to perform what it can. Likewise, both facilities will need the results of the workup. The transferring facility’s medical director is in charge of the investigation to ensure that there were no errors that caused the reaction. The receiving facility physician in charge of the patient will need the results to properly treat the patient.
MLO’s “Tips from the clinical experts” column provides practical, up-to-date solutions to readers’ technical and clinical issues from experts in various fields. Readers may send questions to [email protected].
