4.22: Sample Analysis II

A technologist is working alone on the third shift in a hospital’s chemistry stat ('rapid response') laboratory. The technologist receives, simultaneously from the emergency room, five specimens for analysis. They are: a) a serum sample for a renal profile (Na, K, Cl, CO2, glucose, BUN, creatinine), b) a blood gas, c) a serum sample for potassium and glucose, d) a serum beta-hCG (“pregnancy” test), e) a sample for urinalysis (dipstick plus microscopic).

QUESTIONS

1. What should be the order in which these samples are analyzed?
2. Ten minutes after the first five samples arrived, another blood gas specimen arrives in the laboratory. Will this specimen affect the order of the analysis of the remaining specimens? Why?

Questions to Consider

1. What clinical and laboratory factors should the technologist consider in deciding upon the order of analysis?
2. What, if any, acute emergency situations might be most comonly associated with each of these types of specimens?
3. For which of the situations discussed in question #2 would the physician’s potentially life—saving medical decision-making be most likely to depend on the laboratory results?

Answer

1. The best order of work would most likely be: a) Run the blood gas specimen immediately. b) While the blood-gas analysis is being performed (approximately 2 minutes), set up blood samples (specimens a, c, d) to centrifuge if they are clotted. While the samples are centrifuging (approximately 8-10 minutes), the technologist should get the reagents ready for the pregnancy test and, if necessary, calibrate the instrument that will perform the renal profile. If time is still available, the dipstick analysis can be performed on the urine sample before it is centrifuged. c) When the blood-gas analysis is complete, enter and verify the results. Then set up the pregnancy test, which requires 7-10 minutes to obtain a negative result, and it is probably best to get the incubation period going since this test’s clinical priority is very high. Next analyze the serum specimens in the order of d) Glucose and potassium and e) Renal profile. Finally, while the serum samples are being analyzed (10-15 minutes), prepare to do f) Urinalysis.
2. The logic for prioritizing sample analysis does not change; one must assume a blood-gas specimen is needed for immediate medical decision making. The second blood-gas specimen should be analyzed immediately upon receipt before resuming the analysis of the remaining specimens.

Answers to Questions to Consider

1. The most important factor in making a decision on sample priority is the emergency nature of the patient’s condition. The more acute the situation, the faster the laboratory result is required by the physician. An “emergency” can be defined as a potentially life-threatening situation requiring medical intervention within a relatively short period of time - ranging from minutes to several hours.
   
   Many hospitals encourage physicians to communicate with the laboratory and provide information on the medical problem of a patient, drug history, etc. Although this information can be invaluable to the technologist in prioritizing sample processing or interpreting results, it is rarely provided. In addition, in an attempt to get results faster (whether cliniclly needed or not), many physicians order tests "stat.", although that might not be justified on clinical grounds.
   
   The major laboratory factors which must be considered in deciding upon sample priority include sample processing and analysis times. The time for sample processing prior to analysis includes time for allowing serum to clot and centrifugation time. Analysis time includes time for actual measurement and any lengthy incubation times. A lengthy incubation may often need to be started before analyzing the higher priority analyses just to get a lengthier procedure initiated.
2. a) A renal profile does not suggest any acute medical situation. A convenience for physician ordering, this profile might be ordered for both non-emergency and emergency situations. Unfortunately, when such a profile is ordered without an accompanying patient history or presumptive diagnosis, the technologist does not know which situation the physician has encountered. (See Chapters 24, 26.)
   
   b) A blood-gas specimen is difficult to draw and is usually obtained for critical situations involving many types of acute acid-base disorders ranging from pulmonary arrest to ketoacidosis to poisonings. (See Chapter 25.)
   
   c) Glucose and potassium are typically ordered together for some disorder of diabetes: diabetic ketoacidosis (DKA), hypoglycemia, etc. A patient presenting with DKA or hypoglycemia can often be in a critical situation. (See Chapter 32.)
   
   d) A serum (or urine) beta-hCG will be ordered in cases of females of childbearing age presenting with lower abdominal pain. The physician needs to differentiate an ectopic pregnancy as the source of the pain from other sources of pain not associated with pregnancy. Other situations requiring an hCG analysis include those cases of young females requiring some other emergency intervention (surgical, x-rays, etc.). In these cases, the clinician needs to determine whether the patient is pregnant before beginning an intervention that could endanger a fetus. In all cases, some impending intervention by the physician will depend upon the hCG resuls from the laboratory. (Chapter 40.)
   
   e) A urine sample may be ordered in cases of renal failure, possible kidney infection, etc. Rarely are these acute emergency situations. (See Chapter 26.)
3. For specimens a and e, the technologist can have no idea if the physician really requires immediate results to make a medical decision. Results for specimens b, c, and d very likely are needed for acute patient care. Although an ectopic pregnancy is a potentially life-threatening condition, the physician generally does not require immediate results. Therefore, specimens b and c are presumed to require the most rapid analysis.