Are point of care (POC) labs reliable?

Point-of-Care Laboratory Testing Reliability

Point-of-care (POC) laboratory tests are conditionally reliable when used appropriately, but their accuracy depends critically on proper quality control, operator training, specimen collection technique, and understanding device-specific limitations—particularly in critically ill patients where physiologic derangements can significantly compromise results. 1

Overall Performance Standards

POC tests demonstrate excellent specificity (≥99%) across most applications, making false-positive results rare and routine confirmation of positive results generally unnecessary. 1 However, sensitivity varies substantially by test type, clinical context, and timing:

• COVID-19 antigen testing: 81% sensitivity in symptomatic patients, dropping to 63% in asymptomatic individuals 1
• Urine albumin POC devices: Should detect ≥85% of patients with significant albuminuria (ACR ≥30 mg/g) to be clinically useful 1
• Respiratory viral testing: NAAT-based POC tests generally outperform isothermal assays in sensitivity 1

Critical Limitations in Intensive Care Settings

Glucose Monitoring

In critically ill patients, POC glucose meters are substantially less accurate than laboratory enzymatic methods and should be avoided in specific high-risk situations. 1, 2

Mandatory arterial or venous sampling (never capillary) in: 1, 2

• Patients in shock or on vasopressor therapy
• Severe peripheral edema
• Hypotension or impaired microcirculation
• Acidosis or dehydration

Major error sources include: 1, 2

• Hematocrit abnormalities (particularly problematic in neonates)
• Hypoxia and oxygen therapy
• Interfering medications (maltose, galactose, icodextrin)
• Operator errors exceeding instrument limitations
• Slow glucose equilibration during hemodynamic instability

Electrolyte Measurement

For urgent potassium measurement in critically ill patients, use arterial blood gas analyzer results for immediate clinical decisions rather than waiting for central laboratory results. 3

Sampling hierarchy to prevent contamination errors: 3

1. Arterial samples (most accurate, closest to laboratory values)
2. Venous samples (acceptable alternative)
3. Never capillary samples in critically ill patients

Critical technique requirements: 3

• Use only 0.9% sodium chloride (±heparin) for arterial line flush
• Properly discard dead space volume before sampling
• Avoid contamination from multilumen catheter IV infusions

Kidney Disease Testing

POC testing for creatinine and urine albumin is suggested only where laboratory access is limited or POC facilitates clinical pathways, provided rigorous quality standards are maintained. 1

Essential quality requirements: 1

• Same preanalytical, analytical, and postanalytical quality criteria as laboratory testing
• External quality assessment participation
• Manufacturer reporting of accuracy and precision data (currently often lacking)
• Capability to generate eGFR estimates using regionally appropriate equations

Major caveat: Exercise caution interpreting POC eGFR in patients where creatinine may not correlate with GFR due to non-GFR effects (tubular secretion, muscle mass extremes). 1

Coagulation Monitoring in Trauma

POC prothrombin time (PT) testing demonstrates good reliability and accuracy when PT ratio <2.0, but precision deteriorates at higher values. 1

Recommended thresholds: 1

• POC-PTr ≥1.2: Detects moderate traumatic coagulopathy
• POC-PTr ≥1.4: Detects severe traumatic coagulopathy

Viscoelastic methods (ROTEM/TEG): Show comparable outcomes to conventional coagulation tests for guiding transfusion, with potential mortality benefit specifically in traumatic brain injury patients. 1

Infectious Disease Testing

Respiratory Pathogens

CLIA-waived NAAT assays for influenza and RSV are increasingly available, with reverse transcriptase PCR technologies demonstrating higher sensitivity than isothermal assays. 1

Known limitations: 1

• Multiplexed panels may miss closely related viruses or emerging pathogens
• Adenovirus detection often has decreased sensitivity compared to singleplex assays
• Inability to distinguish enteroviruses from rhinoviruses in some panels
• Proprietary primers prevent investigation of emerging viral strains

COVID-19 Antigen Testing

POC and laboratory-based antigen testing show similar diagnostic accuracy (63-70% sensitivity, 100% specificity), making POC acceptable when rapid results facilitate clinical decisions. 1

Performance varies by clinical context: 1

• Symptomatic patients within 5 days of symptom onset: 89% sensitivity
• Symptomatic patients after 5 days: 54% sensitivity
• Asymptomatic individuals: 63% sensitivity

Common Pitfalls and Risk Mitigation

Operator error exceeds instrument error as the primary source of POC test inaccuracy. 2, 4

Essential quality control measures: 1, 2

• Regular device calibration and maintenance
• Proper test strip/reagent storage and handling
• Standardized specimen collection protocols
• Verification of out-of-range results with laboratory testing
• Ongoing operator training and competency assessment
• Awareness of medication and physiologic interferences specific to each device

Regulatory compliance requirements: 1, 5

• Appropriate validation prior to clinical use
• Proficiency testing participation
• Documentation of quality control procedures
• Performance enhancement programs

When Laboratory Testing is Mandatory

Confirm POC results with central laboratory testing in: 1

• Extreme glucose values (very high or very low)
• Positive semiquantitative urine albumin screening tests
• Discordance between clinical presentation and POC result
• Critical treatment decisions requiring highest accuracy (e.g., insulin initiation in DKA when K+ <3.3 mEq/L) 3

Laboratory enzymatic methods remain the gold standard with coefficient of variation ≤2.7% at clinically relevant concentrations. 2