Section 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 clinically relevant range of values that would be expected in specimens of patients on drug therapy and that cover the level of clinical significance for the particular drug. The samples may be provided through mailed shipments or, at HHS' option, may be provided to HHS or its designee for on-site testing.(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. Analyte or Test Procedure
Alcohol (blood)
Blood lead
Carbamazepine
Digoxin
Ethosuximide
Gentamicin
Lithium
Phenobarbital
Phenytoin
Primidone
Procainamide
(and metabolite)
Quinidine
Theophylline
Tobramycin
Valproic Acid
(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 of ten or more referee laboratories or 80 percent or more of all participating laboratories. The score for a sample in toxicology is the score determined under paragraph (c)(2) of this section.(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 Criteria for Acceptable Performance
The criteria for acceptable performance are:
| Analyte or test | Criteria for acceptable performance |
| Alcohol, blood | Target Value ±25%. |
| Blood lead | Target Value ±10% or 4 mcg/dL (greater). |
| Carbamazepine | Target Value ±25%. |
| Digoxin | Target Value ±20% or ±0.2 ng/mL (greater). |
| Ethosuximide | Target Value ±20%. |
| Gentamicin | Target Value ±25%. |
| Lithium | Target Value ±0.3 mmol/L or ±20% (greater). |
| Phenobarbital | Target Value ±20% |
| Phenytoin | Target Value ±25%. |
| Primidone | Target Value ±25%. |
| Procainamide (and metabolite) | Target Value ±25%. |
| Quinidine | Target Value ±25%. |
| Tobramycin | Target Value ±25%. |
| Theophylline | Target Value ±25%. |
| Valproic Acid | Target Value ±25%. |
(3) To determine the analyte testing event score, the number of acceptable analyte responses must be averaged using the following formula: View Image
(4) To determine the overall testing event score, the number of correct responses for all analytes must be averaged using the following formula: View Image
57 FR 7151, Feb. 28, 1992, as amended at 58 FR 5229, Jan. 19, 1993; 68 FR 3702, Jan. 24, 2003