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Clinical Biochemistry

Introduction

The Clinical Biochemistry Laboratories offers a comprehensive repertoire of laboratory tests ranging from stat/routine tests of renal, liver, cardiac, respiratory functions to highly specialized tests for hormones, tumour markers, trace metals, vitamins and therapeutic drug monitoring; to help clinicians in the diagnosis and management of a wide variety of diseases. Analyses of biochemical constituents are conducted in blood, urine, and other body fluids (such as cerebrospinal fluid, pleural fluid, ascitic fluid, etc).

Requests and Specimens for Biochemical Tests

Prior to sending requests and specimens for biochemical tests, it is advisable to establish clarifications with regard to the nature of specimen, time of collection, type of container and necessary precautions. As a matter of policy, test cancellations are only allowed if the laboratory has not performed the test at the time of notification.

Correct specimen labelling is expected – missing requesting doctor's name, MCR number and signature, unlabelled specimens, mismatched patient's identity on specimen tube and request form, or wrong specimen type may result in rejection of the test request and specimen.

Pre-analytical Variations

To avoid interference from preanalytical variations arising from circadian or diurnal factors, food intake, body posture and stress, specimens should be collected with the patient in the fasting state (e.g. before breakfast between 7am to 9am) and in a seated position, unless otherwise stated.

Timing of specimen collection is particularly important for biochemical constituents that undergo marked diurnal variation and for those used to monitor drug therapy.


For analytes affected by strenuous physical activity or exercise, such as creatine kinase (CK) and myoglobin, it is advisable to allow the patient an adequate period of rest before specimen collection.

Pre-analytical variations arising from specimen collection procedures and specimen delivery and storage are described in the following sections.

Collection of Blood Specimens

Venous blood is used for most tests while arterial blood is required for blood gas and blood pH measurements.

Venepuncture Sites

Inappropriate sites for venepuncture include:

  • Arms with fistulas or vascular grafts
  • Arm on side of mastectomy
  • Arm in which blood is being transfused or IV fluid being administered
  • Sites above an IV canula
  • Veins on lateral and palmar surface (underside) of the wrist
  • Infected sites
  • Scarred areas
  • Edematous areas
  • Haematomas
  • Extremity affected by stroke and injury

Do not collect blood specimens from the arm which an intravenous infusion is being administered, as this will cause erroneously high results for the analytes which are contained in the infused fluids and low results for other analytes due to dilution. Specimens obtained from the opposite arm are preferred.

Preparation of the Site

Ensure complete drying of alcohol-swabbed skin before inserting needle for blood collection. Alcohol may cause hemolysis of red cells and invalidate test results.

Precautions during Venepuncture

Prolonged tourniquet application, fist clenching and trauma to surrounding tissues (following excessive tapping of venepuncture site to enhance prominence of the vein) can result in haemolysis and spuriously high levels of serum potassium, LDH, CK, AST and phosphate. Haemolysis can also result in spuriously low levels of insulin. At the extreme, badly haemolysed samples are not suitable for analysis.

Prolonged tourniquet application (it is recommended that the tourniquet be released soon after the needle enters the vein) may also result in raised protein levels and concomitantly that of substances bound to them, e.g. cholesterol, calcium and drugs.

Collection of Venous Blood

For most of the tests, serum is required and blood need to be collected in a plain tube preferably containing clot activator and separator gel.

For other tests, whole blood or plasma is required and blood should be collected with specific anticoagulants. Fill the container up to the inscribed mark to prevent excessive dilution of the biochemical constituents by anticoagulant.

Please refer to the test list for the specific anticoagulant needed; as collecting specimens with a wrong anticoagulant will invalidate test results and may result in rejection of the test request and specimen. For example:  clotted specimens for HbA1c, G6PDH and Immunosuppressive drug (Cyclosporine, Tacrolimus, Sirolimus, Everolimus) requests (due to lack of appropriate anticoagulant) will be rejected.

Collection of Arterial Blood for Blood Gas and Acid-base Status

For the assessment of blood gas and acid-base status of patients, collect 3mL of arterial blood in a syringe containing heparin (preferably in a dried form).

Care must be taken to ensure that there is no air space in the syringe and air bubbles present in the syringe expelled: remove the needle, hold the syringe upright (nozzle at the top), gently tap on the side of the syringe to bring the air bubbles to the top, press the plunger to expel the air bubbles. Tightly seal the syringe nozzle to avoid exposing collected blood to air. The syringe should be gently rotated between the palms of the hands to ensure good mix of blood and heparin. The specimen should then be clearly labelled, placed in a biohazard bag and immersed in another bag with crushed ice and despatched immediately to the laboratory.

Order of Draw for Multiple Blood Specimens

When multiple blood specimens are required to be collected in different specimen tubes, to minimise potential pre-analytical errors due to cross-contamination from or carry-over of specimen tube additives or anticoagulants, the recommended order of draw (CLSI Guidelines GP41, 7th Edition, 2017, "Collection of Diagnostic Venous Blood Specimens") is as follows:

  1. Sterile specimens (e.g. blood cultures)
  2. Citrate tubes (tri-sodium citrate) / ACD tubes (tri-sodium citrate, citric acid, dextrose)
  3. Serum tubes (plain, with or without clot activator or separator gel)
  4. Heparin tubes (lithium heparin)
  5. EDTA tubes (potassium EDTA)
  6. Fluoride-Oxalate tubes (sodium fluoride/potassium oxalate)

Immediately after filling any specimen tube which contains an additive, gently invert tubes for the required number of inversions per the manufacturer's instructions to ensure proper mixing of blood with additives or anticoagulant.

If using the Becton Dickinson (BD) Vacutainer® evacuated blood collection system, for proper additive performance, the collection tubes should be inverted according to the following recommendations by BD:

  1. SST and serum tubes – 5 inversions
  2. Additive tubes (EDTA, Heparin, Fluoride-oxalate) – 8 to 10 inversions
  3. Sodium Citrate tubes – 3 to 4 inversions

If using other blood collection systems, please consult the manufacturer's instructions for the required number of inversions to ensure proper mixing of blood.

For multiple tube collections, the blood can be mixed while the next tube is filling. To avoid foaming or haemolysis, the blood must not be mixed vigorously.

Collection of Urine Specimens

Urine specimens should be collected in a sterile container and sent to the laboratory immediately after collection.

Timed Urine Collections

It is very important that timed urine collections (24 hour or shorter periods) should be collected with great care. Clear instructions to the patient are essential and include emptying of the bladder at the start of the collection period (discarding this urine sub-collection) and at the end of the collection period (keeping this urine sub-collection). Patients should be instructed to save the urine sub-collections at the time of defecation and while taking a bath. These instructions are particularly important for short timed collections, where errors may be amplified if a urine sub-collection is erroneously retained or discarded.

 

Methods of preservation include refrigeration at 2-8 oC or addition of relevant preservatives. Preservatives added to urine collection containers are toxic/corrosive as indicated by the affixed labels. Patients should be instructed not to discard the preservatives but to handle the urine collection containers and their contents with care, and to keep them out of reach of children. Urine specimens should be sent to the laboratory as soon as the collection has ended. The whole bottle of urine or an aliquot of approximately 20 - 50 mL in a smaller container may be sent. If an aliquot is to be sent, the contents of the bottle should be mixed thoroughly, its volume measured and written on the request form.

More details on timed urine collection and recommended preservatives for specific tests are found in the list of individual tests.

Random Urine Collections

Random urine can be collected at any time of the day. A mid-stream urine collection is preferred. Mid-stream urine is collected in the middle of a urine flow. To prevent contamination with skin, vaginal or urethral cells and bacteria, the urinary opening should be carefully cleaned and patient pass the first part of the urine flow into the toilet. The mid-stream of the urine flow is collected into the sterile container until the container is filled. The patient then continues to void his/her bladder.  The urine container is then capped tightly, labelled appropriately with patient identifiers, and sent to the laboratory immediately.

First-Morning Urine Collections

For some urine tests, first-morning mid-stream urine is preferred. First morning urine is collected immediately after arising from bed, after having emptied the bladder the night before going to sleep. For patients with atypical work/sleep schedule, this urine can be collected over any 8-hour period. Any urine which is voided during this 8-hour period should be pooled and refrigerated so that an accurate 8-hour specimen is obtained.

Other Urine Collections

Other urine tests which require special instructions include:

  • Urine for Phase Contrast Microscopy: Freshly collected first morning mid-stream urine should be sent to the laboratory immediately. Delay in the specimen reaching the laboratory would cause changes in the appearance of blood cells.

  • Urine for Porphyrins: Urine specimen should be protected from light by wrapping in aluminium foil before sending to the laboratory.
     

Details of specific instructions are found in the list of individual tests.

Collection of Cerebrospinal Fluid (CSF) and Other Fluids

CSF should be collected into a plain sterile container (unless otherwise stated) and sent to the laboratory immediately. Similarly, other fluids, e.g. ascitic, peritoneal etc. should be collected in plain sterile containers and sent to the laboratory immediately after collection If they cannot be sent immediately, they should be stored at 2-8oC.  Certain tests e.g. lactate-in-CSF should be collected in their specified containers.

Delivery and Storage of Specimens

Specimens should be kept at room temperature of 24oC (unless otherwise stated) during transport and delivered to the laboratories as soon as possible (within two hours).

When this is not possible, blood specimens for tests utilising serum or plasma should be centrifuged and the serum or plasma separated from blood cells before storage either in the refrigerator or freezer. If a centrifuge is not available, serum may be collected once the clot has retracted, into a plain container.

Specimens for tests utilising whole blood should be kept at the temperature stated for the relevant tests.  Some tests may also require additional precautions such as cooling to slow metabolic processes and protection from light to prevent analyte breakdown. For this purpose, specimen should be clearly labelled, placed in a biohazard bag and sent in ice; ie. immersed in another bag with crushed ice and despatched immediately to the laboratory.

Details of specific transport and storage precautions are given in the test list.

Please note that certain tests are not amenable for collection at sites remote from our performing laboratories. Details of this list of tests can be found in the Section: Test Request / Media Forms, under section: "Nature of Specimen".

Test Limitations and Interferences

It is important to note that any analytical assay can be subjected to interference which can falsely alter the test result. These interfering factors may interact with various parts of the assay and/or assay detection system producing spurious results. The effect of the interferents may be assay and/or analyser dependent.

Assay interference can have important clinical consequences and may lead to unnecessary clinical investigations and inappropriate treatment, resulting in unfavourable clinical outcomes. It is recommended that clinicians contact the Clinical Biochemistry Laboratory for further discussions should laboratory test results be inconsistent with clinical findings.

Potential interferences may arise from the following endogenous or exogenous sources:

  • Metabolites produced in pathological conditions
  • Substances introduced during patient treatment (e.g. drugs and drug metabolites, therapeutic antibodies, parenteral nutrition)
  • Substances ingested by the patient (e.g. various food and drinks, alcohol, alternative/traditional therapeutic agents, nutritional supplements such as Biotin)
  • Substances added during sample collection or preparation (e.g. anticoagulants, preservatives and stabilisers)
  • Contaminants inadvertently introduced during sample handling from sources (e.g. hand cream, serum separators, collection tube stoppers)
  • Specimen matrix (e.g. haemoglobin, bilirubin, lipids, proteins, endogenous antibodies, excessive analyte concentration)

Interferences of Special Mention

  1. Biotin Interferences

    Biotin (Vitamin B7) is a water-soluble B vitamin found in various foods, as well as multivitamins and dietary supplements (for hair, nail and skin). Biotin concentrations in multivitamins and dietary supplements may contain biotin concentrations ranging 0.015 to 10 mg. High dose supplementation of biotin (>10 mg/day) may also be used for patients with certain inherited metabolic deficiencies/diseases or conditions such as multiple sclerosis (MS).

    While standard intake levels of biotin do not typically cause interference, higher levels may cause significant interference with certain immunoassays that use biotin-streptavidin technology and affect corresponding test results, potentially leading to misdiagnosis. Some of these immunoassays (for hormones, tumour markers, cardiac markers, inflammation markers) used in Clinical Biochemistry Laboratory are biotin-based.

    It is recommended by the Laboratory:

    • Drug history taking by clinicians include query regarding the use of Biotin supplements
    • Abstention, where necessary, for 12 hours (longer if doses are above 10mg and in patients with renal impairment) prior to blood sample collection for laboratory tests
    • Serial testing (as recommended by established clinical practice guidelines) is performed in acute clinical settings especially with cardiac or inflammation markers
    • Clinicians discuss with the Clinical Biochemistry Laboratory when laboratory test results are inconsistent with clinical findings.  

    Details of these biotin-based immunoassays and their precautionary measures are found in the list of individual tests.

  2. Endogenous Antibody Interferences

    Circulating endogenous antibodies such as heterophile, human anti-animal antibodies (e.g. anti-mouse, anti-goat, anti-rabbit), auto-antibodies (e.g. Thyroglobulin auto-antibodies) can cause falsely increased or decreased results for analytes measured by immunoassays, depending on the nature of the interfering antibody and/or the immunoassay design. The magnitude of the effect of these interfering antibodies depends on the concentration of the interfering antibodies but may not be directly proportional. These interfering antibodies may mimic the analyte of interest, the reagent antibodies, or both and can bind to the various parts of the assay detection system producing unreliable results.

    A proportion of the tests (for hormones, tumour markers, cardiac markers, inflammation markers) used in Clinical Biochemistry laboratory are measured by immunoassays. It is recommended that clinicians contact the Clinical Biochemistry laboratory for further discussion should laboratory test results be inconsistent with clinical findings.

Reporting Units

System Internationale (SI) units are used for reporting in general. If on any occasion there is a need for conversion to conventional units, please consult the laboratory.

Reference Intervals

Reference intervals are meant to guide interpretation of laboratory test results and should always be correlated with clinical finding and other clinical investigations.

Whenever possible the reference intervals are established for the local population and non-parametric 2.5th to 97.5th percentiles are utilised. Otherwise published values relevant for the analytical methodology are used after appropriate verification. Where test values between the sexes are not significantly different, only one set of reference interval is used. For some tests, only adult reference intervals are available.

For non-serum/plasma specimens e.g. pleural, ascitic, dialysis, knee or cell culture fluids, or specimens from animals, reference intervals may not be available and the onus will be on the requestor to interpret the results in correlation with clinical findings.

For reference intervals to be included in the patient's test report, age and sex of the patient must be provided in the request form, as reference intervals are age and sex dependent and are appropriate for the registered patient only.

Critical Test Results Notification

Critical results are informed by telephone to the requestor and the communication recorded in the test report. Click here to view the biochemical tests with corresponding critical result levels.

Click here to view all Clinical Biochemistry tests