CBBS: Using pH and glucose dipsticks to screen for contaminated platelets

A Transfusion Service in Mississippi has recently implemented a bacterial screening process for platelets to satisfy the new AABB Standard 5.1.5.1 and the CAP Checklist (MS Word) (PDF) Question Item TRM.44955. The inquiring hospital decided to use Multistix (Bayer) strips to determine the pH and glucose levels of each platelet product prior to transfusion. Their acceptable range for pH is >7.0 and for glucose is >250 mg/dL. These ranges were recommended by a local blood center. All platelet products that do not meet the above specifications are returned to the supplier. Another local blood center has expressed concerns that the pH range used by the inquiring hospital is too strict. The inquiring colleague would like to know if other hospitals are using a similar screening method and if so, what pH range is being used?

Editor's note: Colleagues may find the information at the following links to be germane to this discussion:

1. A colleague who is very familiar with CLIA regulations reports that in his opinion CLIA requires following the manufacturer's instructions, even when (and especially if) a test is waived. Thus, if the multistix test package insert does not state that one of the intended uses of the multistix dipstick test is to test platelet products for evidence of bacterial contamination, the 'assay' becomes a NON-WAIVED test, subject to NON-WAIVED testing compliance conditions. This does not mean that the dipstick testing cannot be done for the purpose of detecting potentially contaminated platelets, but that if the dipstick is used for that purpose, the documentation, quality control, etc., must be compliant with NON-WAIVED testing. THE VALIDATION PROCESS WOULD BE THE MOST CRITICAL STEP, AND SHOULD FOLLOW CLIA GUIDELINES.

A copy of the validation requirements from the CLIA website is shown below.

Sec. 493.1253 Standard: Establishment and verification of performance specifications.

Sec. 493.1253 (a) Applicability. Laboratories are not required to verify or establish performance specifications for any test system used by the laboratory before April 24, 2003.

Sec. 493.1253 (b)(1) Verification of performance specifications.

Each laboratory that introduces an unmodified, FDA-cleared or approved test system must do the following before reporting patient test results:

Demonstrate that it can obtain performance specifications comparable to those established by the manufacturer for the following performance characteristics:
(A) Accuracy.
(B) Precision.
(C) Reportable range of test results for the test system.
Verify that the manufacturer's reference intervals (normal values) are appropriate for the laboratory's patient population.

Sec. 493.1253 (b)(2) Establishment of performance specifications.

Each laboratory that modifies an FDA-cleared or approved test system, or introduces a test system not subject to FDA clearance or approval including methods developed in-house and standardized methods such as text book procedures, or uses a test system in which performance specifications are not provided by the manufacturer must, before reporting patient test results, establish for each test system the performance specifications for the following performance characteristics, as applicable:

Accuracy.
Precision.
Analytical sensitivity.
Analytical specificity to include interfering substances.
Reportable range of test results for the test system.
Reference intervals (normal values).
Any other performance characteristic required for test performance.

Sec. 493.1253 (b)(3) Determination of calibration and control procedures.

The laboratory must determine the test system's calibration procedures and control procedures based upon the performance specifications verified or established under paragraph (b)(1) or (b)(2) of this section.

Sec. 493.1253(c) Documentation. The laboratory must document all activities specified in this section.

2. A colleague at a large hospital in Virginia reports that they have studied the efficacy of using pH and glucose dipsticks to detect units of platelets that might be contaminated with bacteria. The Virginia colleague reports that they found results to be variable and not reliable. Based on their experience, they are now using a glucometer to do glucose testing on their plateletspheresis units, rather than using a glucose dipstick. They do not do the glucose measurement on random platelet concentrates because they primarily transfuse plateletspheresis units. They do not do pH testing on the platelets because they did not find that measurement reliable. What they have found after doing thousands of glucose measurements using a glucometer on plateletpheresis units is that a glucose reading of less than 200 mg/dL may indicate bacterial contamination. Whenever the glucometer reports a glucose result is that low, their microbiology laboratory does a gram stain on the product. The product is cultured if it shows a positive gram stain. To date they have found 157 plateletspheresis units with glucose levels less than 200 mg/dL and 3 plateletspheresis units OUT OF 14,000 TESTED BY THE GLUCOMETER TO BE contaminated with bacteria. If the gram stain is negative and the glucose level is between 150 mg/dL and 200 mg/dL, they transfuse the product as soon as possible but only with pathologist approval; if the glucose level is below 150 mg/dL, they return the platelet to the supplier. Their findings and results of these studies will be published later this year.

3. A colleague from a teaching hospital in Northern California would like to know if the Virginia colleague who submitted response #2 above would be willing to share how they performed the validation for their method.

4. Pending receipt of a response from the Virginia colleague, the Editor provides this comment about their strategy at USC "... we will be relying, at least at first, on the blood product collection agencies (American Red Cross and HemaCare) to perform bacterial detection 'QA' testing on pheresis platelets before those products are shipped to our hospitals. Eventually, we may use a rapid bacterial detection method. More than one such system was on display at the AABB meeting in San Diego. However, as of this writing, I believe that the rapid detection test devices still need 510K approval."

5. A colleague at a large hospital in Virginia reports that they continue to do glucose testing on apheresis platelets (see previous comment from Sept 7, 2003). In order to collect the specimens to do this testing, they use the tubing "tails" on the apheresis platelets. They gently mix the platelet bag and strip the platelets into the primary bag with the blue clamp on the tubing or with the hand stripper. This gentle mix and strip is repeated 2 additional times and then a 1 1/2 inch segment is heat sealed and cut (with scissors) from the tubing at plastic seal. This segment is then cut (again with scissors) and a drop of the platelet contents is placed in the glucometer to measure the glucose level. They have done approximately 6,000 glucoses on platelets by glucometer and find this procedure easy enough to do. This method could be used to obtain a specimen for dipstick testing also.