Pre-analytical Variables Affecting the Integrity of Human Biospecimens

Introduction

Biorepositories or biobanks function to collect, process, transport, and store biospecimens. The integrity of these biospecimens is crucial for the success of clinical trials and research. There are many factors that can influence the results within research such as:

  • Pre-analytical environmental or biological variables

  • Pre-analytical technical variables

  • Analytical variables

  • Post-analytical variables

Pre-analytical variables are defined as factors that can have an impact before the start of the analytical phase. It not only affects the integrity of the tissue samples, but also the results of the analysis. Pre-analytical variables are critical as the analytical integrity of the research can be jeopardized. Seeing as most errors in the laboratory can be attributed to pre-analytical errors this stage is of upmost importance.

Pre-analytical Factors in the Collection of Biospecimens

It is important to adhere to guidelines for general laboratory safety. The collection of biospecimens require a balance of:

  • Accrual rate

  • Types of biospecimens

  • Sample size

  • Costs

  • Location

  • Storage requirements

  • Transport logistics

The biospecimens collected can be either invasive or noninvasive. Biospecimens that are collected through non-invasive methods may lead to an increase in sample size due to easiness of collection, reduced costs, and willingness of donor to participate. This method is especially important when dealing with pediatric biobanking. It is important that biological and environmental factors are standardized and documented when interpreting results as it can affect the downstream analysis. It is also vital to take measurements to observe the effects of intervention and the changes over time.

Pre-analytical Factors That Affect the Collection of Blood Samples and Its Derivatives

The collection of blood samples should be performed by trained staff. Those that are involved in collecting samples from children should specialize in pediatric phlebotomy. The staff needs to be highly trained as this ensures the highest quality of specimens and prevents the donors from experiencing any kind of discomfort. Depending on the research requirements different additives may be required. Different types of additives are coded using different colored collection tubes. Some of the important pre-analytical factors to take note of include:

  1. Using the same tube brand and the same lot number throughout the study. This would be ideal as different brands can have different anticoagulants, additives, and may introduce bias.

  2. Another important factor is the expiration dates on the tubes as the vacuum in these tubes can decrease with age and negatively impact the blood draw and filling of the tube.

  3. Using the same posture such as supine, standing, or supine as these can cause plasma volume changes that may lead to increased analyte levels.

  4. Using the recommended needle gauge as a needle that is too thin can lead to hemolysis that distorts the potassium concentrations and hematological cell counts.

  5. Using the recommended and same duration of tourniquet use as prolonged use can cause changes in analyte concentrations and hemoconcentration.

  6. Avoid inadequate filling as this can result in inaccurate results due to the decrease in blood and additive ratio.

A general rule for common analyses is to use ethylenediaminetetraacetic acid for hematology, DNA, hemoglobin A1C, and a range of proteins. For plasma glucose, it is recommended to use sodium-fluoride tubes while lithium heparin plasma can be used for assays such as kidney function, iron parameters, liver enzymes, thyroid hormones, C-reactive protein, and more.

In remote sites that are resource-poor, capillary dry blood spot (DBS) are easy biospecimens that can be collected. Small volumes of capillary blood from the peripheries can be deposited onto specific paper cards and dried at room temperature for three to four hours. DBS can be used in many analyses. However, some of the pre-analytical variables to note are:

·         Type of collection paper used

·         Type of chemical used in the manufacturing of the paper

·         Thickness of paper

·         The volume of blood deposited

·         Environmental factors such as heat, humidity, sunlight, and moisture

In DNA and RNA collection, there are also biological factors that can affect the biospecimens. These include the donor’s:

·         Gender

·         Age

·         Body mass index

·         Tobacco consumption

Since RNA is more vulnerable to degradation, some of the preanalytical collection factors that can affect the integrity are:

  • Tube additive

  • Tube type

  • Tube sterility

  • Type of biospecimen

  • The volume of blood collected

  • Short-term storage temperature

  • Lag time until extraction

In microRNA’s, the pre-analytical variables include:

  • Diet

  • Age

  • Race

  • Exercise

  • Drugs

  • Altitude

  • Tobacco use

  • Chemicals

  • Hemolysis

  • Coagulation times

  • Temperature

Pre-analytical Factors That Affect the Collection of Urine and Saliva

Urine can be collected in many different ways as it can be used for measurements of many analytes. In urine biospecimens, the preanalytical requirements can be conflicting.  This may result in the requirement of multiple biospecimens. Some of the preanalytical variables for urine collection include:

  • Collection method

  • Environmental exposure

  • Urine dilution

  • Dipstick components

  • Preservatives or additives used

For saliva, these biospecimens have many advantages as they are easy to collect and can be used in many situations especially if donors are afraid of needles. The preanalytical variables for this biospecimen include:

  • The time of collection

  • The temperature the specimen is stored

  • The collection method

Conclusion

The factors mentioned are pre-analytical variables that affect the biospecimens during the collection phase. However, it is important to note that there are many more pre-analytical variables that can affect the integrity of the biospecimens during the processing, transport, and storage phase.