9.1 Procedural Definition: What Is This Test About?

Increased whole blood lactate concentration measured by a lactate meter reflects a switch from aerobic to anaerobic metabolism and is often seen in diseases associated with tissue hypoxia due to hypoperfusion or hypoxemia, diseases that are associated with decreased oxygen utilization and renal disease associated with decreased glomerular filtration rate (GFR) with decreased clearance of lactic acid produced during normal metabolic activity. In addition, hyperlactatemia can be seen when there is an increase in oxygen utilization. A small amount of lactate is produced in the healthy animal because of anaerobic respiration. If oxygen is not available or cannot be used by the tissues, the pyruvate produced by glycolysis results in the production of lactic acid rather than being fully oxidized in the mitochondria to produce adenosine triphosphate. Increased anaerobic metabolism in the hypoxic environment results in less energy production per glucose molecule and produces excess lactic acid, resulting in decreased tissue and blood pH (acidemia).

Several studies have evaluated and compared the use of the handheld lactate meter for use in the dog and cat [1, 2].

9.2 Procedural Purpose: Why Should I Perform This Test?

The measurement of whole blood lactate is used primarily as a prognostic indicator in the critically ill patient. Diseases that result in significant hyperlactatemia include:

• diseases associated with decreased availability of oxygen
  
  
  
  • decreased tissue perfusion
    
    
    
    • cardiac insufficiency
      
    • distributive shock – sepsis
      
    • hypovolemia
      
      
      
      • dehydration
        
      • hemorrhage
    
    
  • decreased blood oxygen‐carrying capacity
    
    
    
    • anemia
      
    • methemoglobinemia
      
    • carbon monoxide toxicity
    
    
  • decreased blood oxygenation
    
    
    
    • pneumonia
  
  
• diseases associated with increased oxygen utilization
  
  
  
  • seizures
    
  • excessive exercise or exercise without adequate training
  
  
• disease associated with decreased oxygen utilization
  
  
  
  • sepsis without distributive shock.

Measurement of whole blood lactate is indicated in any patient with clinical evidence of alterations in oxygen utilization including:

• pale, hyperemic, or cyanotic mucous membranes
  
• significant tachyarrhythmia/dyspnea
  
• fever
  
• seizures
  
• thready pulse
  
• marked dehydration
  
• collapse
  
• peritoneal fluid accumulation with clinical signs suggestive of sepsis.

An additional use of the measurement of lactate is evaluation of body cavity fluid lactate in comparison with whole blood lactate. Lactate concentration in body cavity fluids can increase in association with sepsis or neoplasia. There is insufficient consensus in the literature concerning the specificity of fluid lactate concentration in the identification of sepsis. However, comparing the fluid lactate concentration to peripheral blood lactate concentration appears to be much more specific and warrants culture if bacterial agents are not identified in the cytologic preparations of the fluid [3]. A differential lactate concentration of greater than 2 mmol/l between the fluid and peripheral blood is strongly indicative of sepsis. Lactate concentration also increases in neoplastic effusions. Both neoplastic cells and microbial organisms can increase lactate due to their metabolic use of glucose within the fluid.

9.3 Equipment

The following equipment is used in performing this test:

• lactate meter
  
• lactate reagent strips
  
• syringe and needle
  
• microhematocrit tubes
  
• control product (recommended).

9.4 Procedural Steps: How Do I Perform This Test?

This procedure is for testing when using freshly collected capillary whole blood and describes the general steps involved in the lactate meter. Each lactate meter will have a specific protocol in the instruction manual, which should be closely adhered to when performing a lactate determination test.

9.5 A Note on Quality Control

Most instruments supply a control product. A control test can be done before using a patient sample to ensure that the instrument is working properly or for troubleshooting the instrument. See the instrument manual for proper use of the control product recommended by the manufacturer.

• The procedure for performing the control test is the same as that for the patient’s sample. However, there are additional aspects regarding expiration dates to keep in mind.
  
  
  
  • Like the test strips, the control product will have an expiration date. In most cases, the expiration date for storing the unopened control product is fixed. Once the product is opened, it may have an expiration date based on the date it is opened.
    
  • For example, the fixed expiration date for a control product is 4/12/2022 but the product cannot be used after three months of being opened. If the product was opened on 3/13/2022, it will expire on 4/12/2022. If it is opened on 12/2/2021, it will expire on 3/2/2022. To be sure that these dates are monitored, each vial of control product should have the date it is opened written on the vial.
    
  • Control products usually come in small dropper bottles. Prior to introducing the product, wipe the tip with tissue and discard the first two drops. Introduce the control product into the test strip using the dropper bottle. This is the same protocol for using the control product as described in Chapter 7 for use of the glucometer.