From the Guidelines
A serum bicarbonate test is done by drawing a blood sample from a vein, typically in the arm, using a needle and collection tube, and is crucial for monitoring metabolic acidosis in patients with chronic renal failure, as indicated by studies such as 1. The test measures the level of bicarbonate, a form of carbon dioxide, in the blood serum. To perform the test, a healthcare professional will clean the skin at the collection site with an antiseptic, apply a tourniquet to make the vein more visible, insert a needle into the vein, and collect the blood in a tube. The sample is then sent to a laboratory where it's analyzed using automated chemistry analyzers. No special preparation is typically required before the test, though fasting may sometimes be recommended. The procedure takes only a few minutes, with results usually available within 24 hours. This test is important for assessing acid-base balance in the body and can help diagnose conditions like metabolic acidosis or alkalosis, kidney problems, or respiratory disorders. Normal bicarbonate levels typically range from 23 to 29 mEq/L in adults, though reference ranges may vary slightly between laboratories. Key points to consider when interpreting serum bicarbonate test results include:
- Monitoring frequency: patients with GFR 30 ml/min per 1.73 m2 should be monitored for acidosis (serum bicarbonate concentration) at least every three months, as recommended by 1.
- Correction of metabolic acidemia: maintaining serum bicarbonate at or above 22 mmol/L should be a goal of management, as suggested by 1.
- Treatment options: higher dialysate bicarbonate concentrations, oral supplementation with bicarbonate salts, or a combination of both may be used to correct metabolic acidemia, as discussed in 1.
From the Research
Serum Bicarbonate Test Procedure
The serum bicarbonate test can be done using either arterial or venous blood samples.
- The test involves collecting a blood sample from the patient, which can be done using a needle and syringe or a Vacutainer tube 2.
- The blood sample is then analyzed using a blood gas machine to measure the pH, bicarbonate, and potassium concentrations in the blood 2.
- The phlebotomy technique used to collect the blood sample can affect the accuracy of the serum bicarbonate values, with factors such as prolonged tourniquet time and underfilling of Vacutainer tubes potentially leading to errors in the results 3.
- To ensure accurate results, it is recommended to use a suitable needle size and to fill the Vacutainer tubes to the recommended volume 3.
- The test can be used to assess pH, bicarbonate, and potassium concentrations in critically ill patients, and venous sampling alone is sufficient for this purpose 2.
Key Considerations
- The choice of needle size does not significantly affect serum bicarbonate values 3.
- Prolonged tourniquet time can result in a statistically significant elevation of serum bicarbonate, although this may not be clinically meaningful 3.
- Underfilling of Vacutainer tubes can significantly influence the accuracy of serum bicarbonate values, leading to spuriously low results 3.