#### § 493.937 Toxicology.

(a) *Program content and frequency of challenge.* To be approved for proficiency testing for toxicology, the annual program must provide a minimum of five samples per testing event. There must be at least three testing events at approximately equal intervals per year. The annual program must provide samples that cover the full range of values that could occur in patient specimens and that cover the level of clinical significance for the particular drug. The samples may be provided through mailed shipments.

(b) *Challenges per testing event.* The minimum number of challenges per testing event a program must provide for each analyte or test procedure is five serum, plasma, or blood samples.

| Acetaminophen, serum. |
| --- |
| Alcohol (blood). |
| Blood lead. |
| Carbamazepine, total. |
| Digoxin, total. |
| Gentamicin. |
| Lithium. |
| Phenobarbital. |
| Phenytoin, total. |
| Salicylate. |
| Theophylline. |
| Tobramycin. |
| Valproic Acid, total. |
| Vancomycin. |

Table 1 to Paragraph (b)—Analyte or Test Procedure

(c) *Evaluation of a laboratory's analyte or test performance.* HHS approves only those programs that assess the accuracy of a laboratory's responses in accordance with paragraphs (c)(1) through (4) of this section.

(1) To determine the accuracy of a laboratory's responses for quantitative toxicology tests or analytes, the program must compare the laboratory's response for each analyte with the response that reflects agreement of either 80 percent or more of 10 or more referee laboratories or 80 percent or more of all participating laboratories. Both methods must be attempted before the program can choose to not grade a PT sample.

(2) For quantitative toxicology tests or analytes, the program must determine the correct response for each analyte by the distance of the response from the target value. After the target value has been established for each response, the appropriateness of the response must be determined by using fixed criteria based on the percentage difference from the target value.

| The criteria for acceptable performance are—Analyte or test | Criteria for acceptable performance |
| --- | --- |
| Acetaminophen | Target value ±15% or ±3 mcg/mL (greater). |
| Alcohol, blood | Target Value ±20%. |
| Blood lead | Target Value ±10% or ±2 mcg/dL (greater). |
| Carbamazepine, total | Target Value ±20% or ±1.0 mcg/mL (greater). |
| Digoxin, total | Target Value ±15% or ± 0.2 ng/mL (greater). |
| Gentamicin | Target Value ±25%. |
| Lithium | Target Value ±15% or ±0.3 mmol/L (greater). |
| Phenobarbital | Target Value ±15% or ±2 mcg/mL (greater). |
| Phenytoin total | Target Value ±15% or ± 2 mcg/mL (greater). |
| Salicylate | Target Value ±15% or ±2 mcg/mL (greater). |
| Theophylline | Target Value ±20%. |
| Tobramycin | Target Value ±20%. |
| Valproic Acid, total | Target Value ±20%. |
| Vancomycin | Target Value ±15% or ±2 mcg/mL (greater). |

Table 2 to Paragraph (c)(2)—Criteria for Acceptable Performance

(3) To determine the analyte testing event score, the number of acceptable analyte responses must be averaged using the following formula:

(4) To determine the overall testing event score, the number of correct responses for all analytes must be averaged using the following formula:

[57 FR 7151, Feb. 28, 1992, as amended at 58 FR 5229, Jan. 19, 1993; 68 FR 3702, Jan. 24, 2003; 87 FR 41240, July 11, 2022]