A clinical laboratory scientist performs 30 replicate hemoglobin ...

[Anajune7]

A clinical laboratory scientist performs 30 replicate hemoglobin determinations on a single blood sample. When statistics are used to determine the precision of the method, the mean is 13.8 g/dL and 1 SD is 0.1 g/dL.
 
  This means that 95.5 of the results on this specimen lie:
 
  a. Between 13.4 and 14.2 g/dL
  b. Between 13.6 and 14.0 g/dL
  c. Between 13.5 and 14.1 g/dL
  d. Between 13.7 and 13.9 g/dL

Question 2

The following hemoglobin results, reported in g/dL, are obtained on a hospitalized patient on 3 consecutive days:
 
  Day 1 Day 2 Day 3
   14.3 11.5 14.4
 
  The SD for this hemoglobin method was calculated in Question 18. A delta check was obtained on day 2. Controls were run as appropriate each day and were all within limits for this procedure.
 
  What is the most probable reason for the day 2 result when compared with those for days 1 and 3?
 
  a. It is within the 95.5 confidence levels for this test.
  b. It may represent an error in patient identification.
  c. The patient had a major blood loss between days 1 and 2.
  d. It is within the 99 confidence levels for this test.

[janeli1]

Answer to Question 1

ANS: B
Because 1 SD is 0.1 g/dL, 2 SD = 0.2 g/dL. Thus 95.5 of the results lie between 13.6 (2 SDs) and 14.0 (+2 SDs).

Answer to Question 2

ANS: B
The results for days 1 and 3 are statistically the same result (i.e., they are within the 95.5 confidence levels for this procedure and are therefore precise). The result for day 2 is clearly very significantly different, thus giving a delta check (the only possible explanation of those given here is that a patient identification error occurred and the specimen on day 2 is from a different patient). Delta checks are designed to help pick up this kind of critical error. If it had been within the 99 confidence limits, then it would have been within 3 SDs or no less than 14.0 g/dL. Because the results from day 1 and day 3 are the same, blood loss with a drop in hemoglobin cannot explain the day 2 results.

[Anajune7]

Excellent

[connor417]

Gracias!