Clinical Biochemistry

The overall clinical penetrance in terms of iron overload-related clinical symptoms is less than 30% in HFE-associated hereditary hemochromatosis. Ferritin is the most reliable biomarker to quantify iron load but may be falsely elevated during an acute phase response as in inflammation, stress, or infections. In the investigation of clinical hereditary hemochromatosis, don’t order HFE C282Y testing unless BOTH the ferritin and the transferrin saturation are elevated. A normal ferritin rules out a clinically treatable hemochromatosis syndrome and is therefore an appropriate first line test. Transferrin saturation can be added on to the same blood sample if the ferritin is elevated.

The lifespan of a red blood cell (RBC) is approximately 90-120 days, thus the effects of a patient’s change in behaviour, diet, or newly adjusted medications will not be reflected in the HbA1c measurement until most of the previous RBCs in circulation are replaced (~90 days). Therefore, testing at time intervals earlier than 3 months does not allow enough time to pass to reach the treatment target or new steady-state. Overtesting may lead to unnecessary regimen changes, adverse effects, and higher costs. Testing at 6-month intervals may be considered when glycemic targets are consistently achieved. In pregnant patients with pre-existing diabetes, more frequent HbA1c measurements may be appropriate based on clinical guidelines (i.e. at each trimester).

Tissue transglutaminase IgA antibody (anti-tTG IgA) is the recommended first-line screening test for celiac disease as it provides the best diagnostic sensitivity and specificity. Serum IgA concentrations should be considered to rule out IgA deficiency. The addition of tissue transglutaminase IgG antibody (anti-tTG IgG), or deamidated gliadin peptide antibodies (anti-DGP IgG or IgA) in the initial screening will reduce the diagnostic performance and may cause misleading results. In particular, testing of anti-DGP antibodies result in a higher false positive rate that can lead to further unnecessary testing and/or endoscopy. Anti-tTG IgG and anti-DGP IgG testing should be reserved for individuals with IgA deficiency. Implementation of an automated reflexive algorithm in the laboratory can streamline the ordering process.

Renal calculi analysis is a laborious and expensive test. In Alberta, 16% of repeated renal calculi tests occurred within ~5 years (88% were repeated within 3 years). However, the repeated test only rarely demonstrated a change in stone composition (5.5% of all repeats). Similarly, the first epidemiology study of urolithiasis in New Brunswick found that 14% of renal calculi tests were repeated within 3 years, and in all cases, there was no compositional change. Both Canadian Urological Association and American College of Physicians do not recommend routinely monitoring calculi composition for recurrent stones. A calculi analysis may be repeated if there are significant systemic and/or urinary abnormalities, or patients do not respond to treatment.

Screening for monoclonal gammopathies should only be performed in patients with unexplained “CRAB” symptoms (hyperCalcemia, Renal insufficiency, Anemia, or lytic Bone lesions) or diseases associated with monoclonal gammopathies. For such patients, serum protein electrophoresis (SPE) should be the initial screening test with follow-up immunofixation electrophoresis (IFE) if indicated. If SPE is negative, serum free light chain (SFLC) testing may be ordered since SPE/IFE + SFLC offers the best sensitivity for detection of monoclonal proteins. If SFLC testing is not available, or if amyloidosis is suspected, 24-hour urine protein electrophoresis (UPE) may be ordered with follow-up IFE if indicated. Random UPE should not be ordered as there is very limited evidence supporting its sensitivity.

Ferritin is recognized as the most sensitive and specific marker of iron storage, and low ferritin alone is diagnostic of IDA in the general population, i.e. uncomplicated cases of IDA. The measurement of iron is a poor biomarker for IDA as it is susceptible to preanalytical factors such as diurnal variation, diet, and exercise, and ultimately does not represent iron storage. In patients with complicating comorbidities (e.g. infection, autoimmune disease, kidney disease, or cancer), ferritin is an acute phase reactant and may be falsely elevated. In this setting, ordering a fasting transferrin saturation is useful to help diagnose iron deficiency together with the ferritin result.

Routine biochemical screening frequently bundles redundant tests when one is sufficient from a screening, diagnostic or monitoring perspective. For example, ALT is a more specific test to detect liver injury compared to AST. AST is rarely needed if the ALT is normal, and AST should only be ordered by physicians with experience in treating liver disorders or monitoring of diagnosed liver fibrosis with a validated score (e.g. FIB-4). Creatinine alone is sufficient to check kidney function because laboratories automatically report estimated GFR; urea is often an unnecessary addition. Uncoupling bundled tests within order sets for initial screening reduces low value testing.

Direct bilirubin is a sub-component of total bilirubin. Total bilirubin assays measure both direct (conjugated and delta) and indirect (unconjugated) bilirubin. When total bilirubin is low or undetectable there is no value in measuring the direct bilirubin level. Limiting direct bilirubin testing to individuals with elevated total bilirubin has been demonstrated to decrease unnecessary testing. Additionally, implementation of a laboratory reflexive testing algorithm for infants, where direct bilirubin is automatically tested when total bilirubin is elevated, has been proposed to accelerate the identification of biliary atresia while also reducing the need for additional blood collections.

Urine drug tests (UDTs) have a limited but important role in managing patients with substance use disorders and should be guided by a care plan that will be meaningfully changed by the results. The unregulated drug market is encumbered by an evolving milieu of drug additives and contaminates which can complicate the interpretation of simplistic urine drug testing. In particular, testing by immunoassay without confirmation by mass spectrometry can fail to detect potent drugs that can be harmful. Immunoassays are also well known for false positives that can mislead patient management. Mass spectrometry testing delivers the most reliable and comprehensive results, but with delayed turnaround time. Clinicians that are considering drug testing should consider consulting with the laboratory for advice on choosing the best test methodology available and for help interpreting the results.

Positive allergen specific IgE (sIgE) tests represent sensitization and not necessarily clinical allergy. This means that IgE against specific allergens may be detectable even when a patient is clinically tolerant of a given food or environmental allergen. The positive predictive value (PPV) of this testing is low unless the specific allergen tests are carefully chosen based on a review of the patient’s clinical history correlated to specific food and/or environmental exposures. Screening panels and indiscriminate batteries of specific allergen tests should be avoided. Positive specific allergen test results in the absence of clinical allergy lead to incorrect diagnosis of allergy, unsuitable treatment and, in the case of food allergies, inappropriate dietary restrictions with potentially negative health consequences.

Clinicians play an important role in reducing environmental impact from clinical laboratory activity. The production, transportation and disposal of laboratory products have an environmental impact which includes, but is not limited to: tourniquets, needles, tubes, labels, and plastic specimen collection bags. Within the laboratory, additional waste is generated from the specimens, reagents and materials used for testing. The large amounts of energy and water consumed to generate results has a significant carbon footprint as well. Moreover, spurious results frequently lead to unnecessary medical follow-up or misguided therapy with further waste of resources and extension of the carbon footprint. Reducing blood work frequency (as appropriate), reflecting on appropriateness of laboratory orders (Using Labs Wisely) and rethinking laboratory orders (checking previous results instead of reordering, limiting duplication) are potential strategies to reduce environmental impact.

Laboratory testing contributes to a significant carbon footprint due to the required infrastructure (i.e. electricity, HVAC, water) and generated waste (i.e. biohazardous waste, plastic consumables). For example, a laboratory with 10 automated analyzers can consume enough water to fill an Olympic-sized pool annually. This is especially relevant as laboratories move towards increased automation and expanding test menus with a constant focus on throughput and turnaround time. While individual laboratories have agency on some of the contributing factors, the carbon footprint of laboratory testing is largely determined by the inherent design of the instrumentation. As such, it is vital that laboratories establish partnerships with the in vitro diagnostics industry to push for material, hardware, and software changes that allow for laboratory testing in an environmentally sustainable manner. There is a growing international movement in sustainable laboratory medicine with some associations already having published formal guidance in this space.

POCT requires a clinical benefit that justifies the costs and a comprehensive quality oversight that meets accreditation standards and mitigates patient risks. POCT is warranted when its absence has negative impact(s) on patient care (e.g. diagnosis delay, inappropriate patient management) and when the need cannot be appropriately met by central laboratory testing. Additional supporting factors include: inaccessibility to central laboratory testing, societal barriers, patient compliance and quality of life, small sample volume, short sample stability. Appropriate implementation requires appropriate personnel, information systems, instrumentation, supplies, and quality measures. A quality management system (QMS) is essential to optimize the total testing process and mitigate errors, by providing comprehensive approaches to apply standards, policies and procedures.

POCT fecal occult blood test (FOBT) is not useful for either cancer screening or gastrointestinal (GI) bleeding workup. Often the test is used ‘off-label’ in the Emergency Department (ED) to assess patients with suspected GI bleeding, iron-deficiency anemia and/or black stools. Although the test is relatively inexpensive and provides quick results, the test has poor diagnostic sensitivity and lacks clinical utility. It has a high false positive rate (e.g. red meat, beet root, NSAIDs or anti-coagulant medication) and potential for false negatives (e.g. vitamin C, time of collection). Given the absence of clinical evidence or guidelines endorsing the use of urgent screening with FOBT, it is recommended that the test be discontinued for such purposes in the ED and acute care settings.

Urine drug screening (UDS) by POCT devices may be used in clinical drug testing to manage patients with substance use disorders or drug intoxication, particularly when the patient contact time is paramount. The primary focus should be on patient safety and achieving pre-defined long-term goals for each patient.  Decisions to use POCT UDS should include consultation with the clinical laboratory, consideration of its risk versus benefit, recognition of its limitations (false positives and false negatives), and possible need for confirmatory testing, (e.g. for positive UDS results). Dilute urine is a potential cause of false results, with many central laboratories including urine creatinine as part of the testing panel. Testing should not be done without a meaningful plan for results. Based on the limitations, POCT UDS should not be used to accuse patients of dishonesty, or as evidence for punitive measures.

Most current POCT cardiac troponin assays, which are typically less sensitive than the more widely used central laboratory assay, require repeat sampling 3 to 6 hours post-admission to adequately rule out myocardial injury. In contrast, central laboratory cardiac troponin assays are highly sensitive and therefore require typically only 1-3 hours serial testing for ruling out myocardial infarction. Cardiac troponin assays measure either troponin T or cardiac troponin I, each with different cut-offs for ruling out myocardial infarction. Even when measuring the same form of troponin, differences in assay methodologies and manufacturers-specific cut-offs can lead to discrepancies between central laboratory and POCT results. The discrepancies could complicate the accurate interpretation of the rise and fall of troponin changes, potentially affecting clinical decisions such as risk stratification and treatment strategies. Therefore, a committee of clinicians and laboratorians should develop a testing algorithm for manufacturer-specific POCT troponin that reflects the specific methodology used.

Urine qualitative hCG POCT has several limitations that could lead to false negative results. These include: a) lower sensitivity during the first 4 weeks of gestation compared to serum hCG, b) unreliable detection of an hCG degradation product that is the major form of hCG excreted in urine during the late first and entire second trimester, c) susceptibility to ‘high-dose hook effects’ that can occur with very high levels of hCG, d) reduced urine excretion of hCG in ectopic pregnancy, toxemia of pregnancy and threatened miscarriage, and e) hCG being undetectable in dilute urine. Given the limitations of urine hCG POCT, quantitative blood hCG should be the test of choice unless urine hCG POCT significantly improves clinical management. Performing urine POCT in settings where blood hCG is accessible in a timely manner can lead to unnecessary duplication and negatively impact patient care.

POCT glucose meters should not be used to diagnose diabetes due to insufficient analytical precision (±15–20% error versus ±6% recommended for diagnosis) and susceptibility to user and environmental errors. They are suitable for self-monitoring and acute care management, but not for diagnostic purposes. Additionally, capillary whole blood (WB) glucose testing is unreliable in patients with poor perfusion, tissue edema, or hypoxemia, which can cause inaccuracies (e.g. pseudohypoglycemia) and lead to dosing errors. Given the potential limitations of POCT capillary WB glucose, use of venous or arterial samples is recommended for critically ill patients to ensure accurate glucose management.

Capillary blood glucose monitoring for type 2 diabetes can help make informed decisions about medical treatment. Multiple studies show that once optimal control is achieved in stable adults with type 2 diabetes, individuals not using insulin or medications linked to hypoglycemia do not significantly benefit from routine glucose monitoring. Unnecessary daily glucose monitoring in this population may result in potential harms, patient inconvenience, and anxiety without corresponding improvements in health outcomes.