Laboratory Medicine Update - September 3, 2008

University of Virginia Health System

Medical Laboratories

"Quality You Expect, Service You Deserve"

LABORATORY MEDICINE UPDATE

September 3, 2008

Stool cultures, slight change in protocol

Beginning 9-01-2008, the Clinical Microbiology laboratory will include an additional culture media for several non-enteric organisms in stool samples when a routine stool culture is ordered. This change is required to make the diagnostic algorithm consistent with standard practice in Clinical Microbiology. The previous routine stool culture was for the detection of Salmonella and Shigella species.  The new protocol will also include the recovery of Staphylococcus species, yeast and Bacillus species.  There will be an additional CPT code (87046) and cost ($56.00) added to the protocol.

If any additional organisms are suspected, as in the past, please special request them in case additional media need to be set up.  Examples are: Vibrio sp. or Yersinia sp.

Other enteric pathogens such as Campylobacter, Clostridium difficile Toxin A&B and Shiga Toxin can be ordered independently and are tested by EIA.  Cryptosporidium and Giardia should also be independently ordered.

MRSA screening protocols

For INPATIENT MRSA screening upon admission, please order only "MRSA Surveillance PCR", then select the specimen type, and schedule the collection.  Culture is not the preferred test for admission screening and should not be used.  "MRSA Surveillance Culture" should only be ordered under the direction of Hospital Epidemiology from an Infection Control Practitioner.

 

Hospital Epidemiology has approved only the following specimen types for MRSA screening (whether done by PCR or culture):

  • Nares Axilla Groin
  • Scar (note location please) Throat Perirectal
  • Ostomy

When the microbiology laboratory receives a specimen type other than those listed above, the test will be cancelled and the comment appended "Specimen does not meet the epidemiologic criteria for MRSA surveillance.  Please contact the laboratory (2-0460) within 24 hours if alternate testing is indicated". Open wounds are not an acceptable specimen source and testing will not be performed if the specimen is labeled as a "Wound".  Healed wounds must be listed as "Scar" in the specimen description in order to be tested.  Please note the location of the scar being sampled.  Please consult Hospital Epidemiology if assistance is needed to obtain the appropriate MRSA screening protocol.

Change to Calculation for estimated Average Glucose from

Hemoglobin A1C Value

The results of a comprehensive study by the A1c-Derived Average Glucose (ADAG) Study Group have been published in Diabetes Care1.  The study followed 507 patients each of whom collected approximately 2700 individual glucose measurements (self-monitored) over a three month period of time.  Hemoglobin A1c values were determined at the end of the study.  Linear regression analysis was used to derive a new recommended equation for estimating the average blood glucose concentration from the measured Hemoglobin A1c result.  Age, sex, diabetes type, race/ethnicity, and smoking status were not found to contribute significant independent information over that provided by Hemoglobin A1c in estimating average blood glucose.

Medical Laboratories implemented the new equation on September 3, 2008.  The results of the new calculation are lower than those generated by calculations based on an earlier study2.  A table of the 2002 calculation compared to the 2008 calculation follows.  Values above 12.0% Hgb A1c are extrapolated from the study data.

 

1Diabetes Care 31:1473, 2008.  http://www.ncbi.nlm.nih.gov/pubmed/18540046?dopt=Abstract

2Diabetes Care 25:275, 2002

 

Calculated Blood Glucose Based on Hgb A1c

Extrapolated Values

A1c value

Old

New

 

A1c value

Old

New

 

A1c value

Old

New

4.5%

83

82

 

8.3%

218

192

 

12.2%

357

303

4.6%

86

85

 

8.4%

222

194

 

12.4%

364

309

4.7%

90

88

 

8.5%

225

197

 

12.6%

371

315

4.8%

94

91

 

8.6%

229

200

 

12.8%

378

321

4.9%

97

94

 

8.7%

232

203

 

13.0%

386

326

5.0%

101

97

 

8.8%

236

206

 

13.2%

393

332

5.1%

104

100

 

8.9%

240

209

 

13.4%

400

338

5.2%

108

103

 

9.0%

243

212

 

13.6%

407

372

5.3%

111

105

 

9.1%

247

214

 

13.8%

414

349

5.4%

115

108

 

9.2%

250

217

 

14.0%

421

355

5.5%

119

111

 

9.3%

254

220

 

 

 

 

5.6%

122

114

 

9.4%

257

223

 

 

 

 

5.7%

126

117

 

9.5%

261

226

 

 

 

 

5.8%

129

120

 

9.6%

264

229

 

 

 

 

5.9%

133

123

 

9.7%

268

232

 

 

 

 

6.0%

136

126

 

9.8%

272

235

 

 

 

 

6.1%

140

128

 

9.9%

275

237

 

 

 

 

6.2%

143

131

 

10.0%

279

240

 

 

 

 

6.3%

147

134

 

10.1%

282

243

 

 

 

 

6.4%

151

137

 

10.2%

286

246

 

 

 

 

6.5%

154

140

 

10.3%

289

249

 

 

 

 

6.6%

158

143

 

10.4%

293

252

 

 

 

 

6.7%

161

146

 

10.5%

297

255

 

 

 

 

6.8%

165

148

 

10.6%

300

258

 

 

 

 

6.9%

168

151

 

10.7%

304

260

 

 

 

 

7.0%

172

154

 

10.8%

307

263

 

 

 

 

7.1%

175

157

 

10.9%

311

266

 

 

 

 

7.2%

179

160

 

11.0%

314

269

 

 

 

 

7.3%

183

163

 

11.1%

318

272

 

 

 

 

7.4%

186

166

 

11.2%

321

275

 

 

 

 

7.5%

190

169

 

11.3%

325

278

 

 

 

 

7.6%

193

171

 

11.4%

329

280

 

 

 

 

7.7%

197

174

 

11.5%

332

283

 

 

 

 

7.8%

200

177

 

11.6%

336

286

 

 

 

 

7.9%

204

180

 

11.7%

339

289

 

 

 

 

8.0%

208

183

 

11.8%

343

292

 

 

 

 

8.1%

211

186

 

11.9%

346

295

 

 

 

 

8.2%

215

189

 

12.0%

350

298