LAB UPDATEFeb. 15, 2006

Dr. Beverly Dickson

HHeparin

IInduced

TThrombocytopenia

An antibody mediated adverse effect of heparin that is importantbecause of its strong association with venous and arterial thrombosis.

Heparin exposure may be any preparation (LMWH) by any route(flushes), and with any dose.

HEPARIN INDUCED THROMBOCYTOPENIA

Clinicopathological Syndrome

Clinical: Thrombocytopenia with or without thrombosis

Serologic: High titer platelet activating HIT antibodies by sensitive antigen and/or activation assays

Clinical Features of HITTiming of thrombocytopenia

Typical onset: between days 5 and 10 after starting heparinRapid onset: < 1 day following resumption of heparin (usually in a patient recently exposed to heparin, who therefore has residual circulating HIT antibodies)

Severity of thrombocytopeniaPlatelet count nadir: < 20,000/µL in 10% of patients; < 150,000/µL in 85% of patients

Thrombosis is common> 50% develop new thrombosisVenous thrombosis: deep venous thrombosis > pulmonary embolism > warfarin-induced venous limb gangrene > adrenal hemorrhagic necrosis* > cerebral sinus thrombosisArterial thrombosis: limb artery thrombosis > stroke syndrome > myocardial infarction > mesenteric artery thrombosis

Absence of petechiae (even with platelets < 20,000/µL)Skin lesions at heparin injection sites

Severity ranges from erythematous plaques to skin necrosisAcute systemic reactions following intravenous bolus heparin

Acute inflammatory or cardiorespiratory signs and symptoms associated with abrupt platelet count fall

Consultative Hemostasis and Thrombosis, 2002, pg358.

Consultative Hemostasis and Thrombosis 2002, pg 359

Heparin-induced Thrombocytopenia

Quinine- or Sulfa-induced Thrombocytopenia

Frequency Approx. 1/100 Approx. 1/10,000

Onset after beginning treatment

5-14 days ≥ 7 days

Platelet count 20 - 150x109/L* < 20x109/L

Sequelae Thrombosis Bleeding

Laboratory testing using patient serum

Heparin-dependent platelet activation; Immunoassay (heparin/PF4 antigen)

Drug-dependent increase in platelet-associated IgG

*Some patients have a fall in platelet count but platelet count remains > 150x109/L

DRUG INDUCED THROMBOCYTOPENIA MECHANISMS

Simposio Internacional CLAHT PERU 2004

HIT ASSAYS

Two Major Classes

Functional activation assays (Serotonin Release Assay):

Infer presence of HIT antibodies based on heparin-dependent, platelet activating properties (washed platelets)

Antigen Assays (Heparin-PF4 ELISA):

Detect HIT antibodies based upon their reactivity with platelet factor 4 (PF4) complexed to heparin or other polyanions (ELISA)

Specificity, %

HIT Diagnostic Assay Sensitivity, % Early Platelet Fall Late Platelet Fall

Platelet SRA 90-98 * >95 80-97 ‡

Heparin-induced platelet aggregation assay

90-98 * >95 ‡ 80-97 ‡

Platelet aggregation test using citrated platelet-rich plasma

35-85 90◊ 82◊

PF4/heparin EIA >90 * >95 50-93

Combination of sensitive platelet activation and PF4-dependent antigen assay

100 * >95 80-97

”Early” refers to a fall in the platelet count that begins within the first 4 d of starting heparin; “late” refers to a fall that begins on day 5 or later. The specificity varies because late thrombocytopenia due to a reason other than HIT may nevertheless show a false-positive HIT antibody result because of subclinical HIT antibody seroconversion. *Sensitivity defined in relation to those patients in prospective studies who had a positive test result when the platelet count fell by ≥50% after ≥5 days of heparin therapy, and in whom the available clinical information (particularly, evidence for alternative explanations for thrombocytopenia and the effect of stopping or continuing heparin) supported the diagnosis of HIT. However, about 30-40% of samples (app. 2% overall) give a repeated “indeterminate” result, and the activation assay is nondiagnostic.‡ Assumes that the heparin-induced platelet aggregation assay test and SRA have similar sensitivity and specificity profiles; other platelet activation end points that may also give acceptable results using washed platelets include detection of platelet-derived micro particles by flow cytometry.◊ Assumes that a 90% specificity in early thrombocytopenia attributable to non-HIT disorders (eg, nonspecific platelet activation related to acute inflammatory proteins) declines to an 82% specificity in late thrombocytopenia that may be attributable to subclinical HIT antibody seroconversion. Clinicopathologic definition assumes that at least one sensitive test result must be positive for diagnosis of HIT; specificity of the activation assay is indicated.

Localization of thromboembolic complications associated with HIT

Type of TEC Number of TECs (%)

Arterial 126 (29.2%)

Limb artery 71 (16.4%)

Thrombotic stroke 26 (6.0%)

Aortic Thrombosis 16 (3.7%)

Myocardial infarction 10 (2.3%)

Other 3 (0.7%)

Venous 306 (70.8%)

Proximal DVT 114 (26.4%)

Pulmonary embolism 103 (23.8%)

Distal DVT 78 (18.1%)

Cerebral vein (sinus) thrombosis 7 (1.6%)

Other 4 (0.9%)

Thromb Haemost 2005:94:132-5.

Simposio Internacional CLAHT PERU 2004

Clinical Assessment: Inclusion Criteria

History of heparin exposure

Thrombocytopenia during and after heparin exposure (<150,000)

Drop in platelet count (<50%) rather than absolute thrombocytopenia

Smaller drop in platelets (especially skin necrosis)

Early-onset of thrombocytopenia with heparin re-exposure caused by circulating antibodies

Platelet count may rarely be normal when patient presents with thrombosis (delayed-onset HIT)

Thrombocytopenia recovers after heparin withdrawalMedian time to platelet count recovery after heparin withdrawal is 4 days

Platelet Monitoring for HITACCP Consensus Conference, 2004

HIT risk >0.1% - platelet count monitoringPatients recently treated with heparin starting UFH

Platelet count baseline within 24 hoursAcute systemic reaction post UFH bolus

Immediate platelet countPatients receiving therapeutic dose UFH

Every other day platelet count until day 14 or UFH stopped, whichever is first

Postoperative patients, UFH prophylaxis(HIT risk >1%)Every other day platelet count until 14 days or UFH stopped.

HIT Patient Risk Groups

1-5% risk (highest)Post-op vascular, ortho, cardiac patients receiving UFH for 1-2 weeks

0.1-1% risk (rare to infrequent HIT)Medical and obstetric patients receiving prophylactic doses of UFH

Post-op patients receiving LMWH

Post-op/critical care patients with UFH flushes

Medical patients receiving LMWH after one or several preceding doses of UFH

HIT

A negative laboratorytest for HIT antibodiesshould never be usedas the sole criterion

for restarting heparintherapy.

HIT CONCLUSIONS

Routine platelet monitoring rather than HIT Antibody studies is most useful to identify patients who are at risk for thrombosisAlthough functional and antigen assays are sensitive in detecting HIT antibodies, neither is completely specific for HIT syndromeThe diagnostic interpretation of these laboratory tests must be made in the context of clinical pretest probability of HIT

Clindamycin Disk Inductive Test for Staphylococcus spp.

“D Test”

• Routinely performed on Staphylococcus that test resistant to erythromycin but are susceptible to clindamycin

• Many MRSA that cause community acquired infections have msrA gene

D TestResistance to macrolides (e.g. erythromycin) can occur by two different mechanisms with the resulting phenotypes noted below:

Mechanism Determinant

(gene)

Erythromycin Clindamycin

Efflux msrA R S

Ribosome alteration

erm R S*

erm R R

(constitutive)

msrA=macrolide streptogramin (type B) resistance

Erm=erythromycin ribosome methylase; encodes enzymes that confer inducible (MLSBi) or constitutive (MLSBc) resistance to MLS agents via methylation of the 23S rRNA

*requires induction to demonstrate resistance

MLS=macrolide lincosamide (e.g. clindamycin) streptogramin (type B)

InducibleClindamycinResistance(erm-mediated)

Helicobacter pyloriTests at PHD

CLO-Test Rapid urease Invasive

HpSA Stool antigen test Non-invasive

Sensitivity SpecificityFDA

approved test for cure

Detects active infection

CLO 80-98% 93-100% Yes Yes

HpSA 92-97% 90-95% Yes Yes

Serology 80-95% 80-95% No No

Helicobacter pylori

AGG/AGA Graded Recommendations 2005

For patients ≤ 55 years without alarm features, the clinician may use either “test and treat” for H. pylori or acid suppression therapy. (A)

Point of Care

Blood Gas (TIS)

ACT

i calcium

creatinine

6+

PT

I-STAT

Additional POC instruments: Hemocue, Accu-Chek, Clinitek, DCA 2000 (A1c)

LimitationsMethod dependent

Technique dependent

Interferences: known and unknownDrugs

Metabolic

Other

Point of Care

Chemical Pathology

Are your hands clean enough for point-of-care electrolyte analysis?

Hugh S. Lam*, Michael H.M. Chan, Pak C. Ng*, William Wong*, Robert C.K.Cheung, Alan K.W. So*, Tai F. Fok* and Christopher W.K. Lam

Departments of *Paediatrics and Chemical Pathology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong

______________________________________________________________________

Pathology (August 2005) 37(4) pp.299-304

The patient is a 75 year old female with history of frequent TIA, recently placed on coumadin

Upon ambulatory clinic visit her I-STAT INR was > 8.0 but Core Lab INR was 4.1

What might cause this discrepancy?→ technique

→ interference

→ reagents

→ instrument malfunction

Case #1 POC/INR

Lupus anticoagulant/anticardiolipin Ab

LMWH

Direct thrombin inhibitors

Daptomycin

POC/INRInterferences

Case #2 ED/I-STAT +6

A middle aged male presented to the ED post grand mal seizure. Patient had a history of hyponatremic episodes secondary to anti-convulsant drug therapy.

I-STAT Core Lab

Na 132 140

K 3.7 4.0

Cl 103 100

BUN 13 10

AG N/A 31

Glu 159 158

Hgb 17 14

A whole blood glucose test strip that delivers plasma-like test results.

Accu-Chek Inform MeterAccu-Chek Comfort Curve Strip

Case #3 ICU/Accu-Chek Inform Meter

The patient is a 75 year old male who was transferred from Lake Pointe in septic shock s/p hernia repair. The patient developed renal failure, liver failure with coagulopathy and respiratory failure. Multiple POC glucoses performed, multiple results discrepant with laboratory.

Date Time* Core Lab

Accu-Chek

Jan 9 0754 109 140

Jan 9 0550 88 129

Jan 8 1415 63 99

Jan 8 1055 59 100

Jan 8 0630 36 75

Jan 8 0350 38 74

* Results charted within minutes of each other

Case #3Metabolic Status

Alk Phos 374 U/L

ALT 407 U/L

AST 2697 U/L

Total Bili 5.4 mg/dL

Lipase 2347 U/L

CK 863 U/L

Creatinine 4.7 mg/dL

TnI 0.5 ng/mL

Calcium 5.5 mg/dL

i Calcium 0.71 mmol/L

Anion gap 24

PT 32.8 sec

INR 3.0

Lactic Acid 10.7 mmol/L

Accu-Chek Comfort Curve Strip

Known Interferences

Galactose

Maltose

Xylose

Bilirubin (> 20 mg/dL)

Lipemia (> 5000 mg/dL)

Acetaminophen

(> 8 mg/dL)

Uric acid

Low Hct (< 20%)

High Hct

> 65% @ ≤ 200 mg/dL

> 55% @ > 200 mg/dL

Mannitol

Icodextrin

60 mg/dL glucose concentration

500 mg/dL glucoseconcentration

Clinica Chimica Acta 356 (2005) 178-183.

Crit Care Med 2005 Vol 33, no.12.

CAPILLARY BLOOD GLUCOMETER VS REFERENCE STANDARD

Crit Care Med 2005 Vol 33, No 12

ARTERIAL BLOOD GLUCOMETER AND REFERENCE STANDARD

Chest 2005: 127:1749-1751.

meters originally designed to test glucose in diabetics with normal hematocrit

ICU patients may suffer from multiple metabolic +/or hematologic derangements

ICU patients may be treated with multiple drugs

Results which do not seem realistic in

view of the clinical assessment should

be repeated in the Core Laboratory.

POC Glucose

Urine Drug ScreenImmunoassay

Does it detect oxycodone?

Basic urine drug immunoassay testing for opiates tests primarily for morphine (heroin and codeine metabolized to morphine).

These tests do not generally detect low to moderate oxycodone use.

STAT Quantitative Serum Toxicology Assays Required to Support the ED

acetaminophen co-oximetry ETOH

lithium digoxin MEOH

salicylate phenobarbital ethylene glycol

theophylline iron

valproic acid transferrin

Oxycodone

To detect compliance, abuse or toxicity

best detected by specific assay detection levels < 100ug/L necessary

Urine Drug Screen Immunoassay

Drug X-reaction

PCP Dextromethorphan, diphenhydramine, sertraline

Opiates Quinolone antibiotics

Amphetamines Detects all types of sympathomimetic amines (including those in OTC diet suppressants and cold medications)