Diagnostics - Exam 1

Front 1

What unit of measurement are used with plasma electrolytes?

Back 1

mEq/L or mg/dL

Front 2

What is plasma osmolality and what largely determines it?

Back 2

A measure of plasma concentration. Sodium is the major determinant of plasma osmolality.

Front 3

How is plasma osmolality mainly regulated?

Back 3

Through thirst and ADH:
- High plasma Osm (or hypotension): normally the pituitary is stimulated to release ADH -> concentrated urine/thirst
- Low plasma Osm: suppresses ADH release -> dilute urine from more excreted water

Front 4

What is the normal plasma osmolality range?

Back 4

275 - 290 mosmol/kg

Front 5

What is urine osmolality and what does it depend on?

Back 5

It is a measure of urine concentration. It depends on the integrity of the ADH-Renal axis.

Front 6

Urine osmolality varies with _______. How so?

Back 6

normal renal function.

Absence of ADH: 50-100 mosmol/kg
Peak ADH effect: 900-1200 mosmol/kg

Front 7

Sodium is the major determinant for ____ _____ and ____ _____ _____.

Back 7

Plasma osmolality and effective circulating volume

Front 8

What is effective circulating volume?

Back 8

The volume of arterial blood effectively perfusing tissue (and producing the blood pressure).

Front 9

What has opposite effects on the kidneys with respect to regulating effective circulating volume?

Back 9

Aldosterone & natriuretic peptides regulate ECF through the kidneys by having them excrete more or less Na+

Front 10

What is a normal plasma sodium level?

Back 10

136 - 144 mEq/L

- High = hypernatremia (+145)
- Low = hyponatremia (-136)

Front 11

Urine sodium (UNa) can be used to estimate _______? What are the limitations of this test?

Back 11

Volume status:
>25 mEq/L normal spot urine
<25 mEq/L hypovolemia

Limits: falsely elevated with high rate of H2O reabsorption (as in acute renal failure)

Front 12

What is a better way than UNa to calculate volume status in a patient with acute renal failure?

Back 12

A fractional excretion of sodium (FENa) would be a better assessment of direct renal sodium handling.

Front 13

What is FENa calculated from? And what does it describe?

Back 13

From a random urine. It describes the ratio of quantity of sodium filtered to that excreted (directly evaluating renal sodium handling)

Front 14

A FENa of <1% indicates?

Back 14

Volume depletion

Front 15

What are causes of hypernatremia?

Back 15

1) Sodium Load (eg, hypertonic NaCl, NaHCO3)
2) Free Water Depletion
- Increased loss
- Osmotic Diuresis
- Diabetes Insipitus

Front 16

Give examples of free water depletion.

Back 16

- Increased loss (sweat, respiratory, osmotic diarrhea)
- Osmotic Diuresis (mannitol, glucose, urea)
- Diabetes Insipidus (can't reabsorb H2O b/c pituitary isn't releasing ADH or ADH isn't working on the kidneys)

Front 17

The cause(s) of hypernatremia MUST be superimposed on ____________.

Back 17

lack of thirst or poor access to water

(⁂ hypernatremia = lack of thirst OR poor access to H20 PLUS sodium load OR free water depletion)

Front 18

In hypernatremia the plasma osmolality is _______.

Back 18

increased

(normal response: release of ADH, ↑H2O reabsorption, more concentrated urine (elevated urine osmolality))

Front 19

The ADH-Renal axis is functioning normally if urine osmolality is _______.

Back 19

>700-800 mosmol/kg

If that is the case, then the hypernatremia is either from sodium load or water depletion

Front 20

If the urine osm is >700-800 mosmol/kg and the urine sodium is <25 mEq/L, then the hypernatremia is caused by________.

Back 20

volume depletion

Front 21

If the urine osm is >700-800 mosmol/kg and the urine sodium is >25 mEq/L, then the cause of hypernatremia is?

Back 21

sodium overload

Front 22

If ADH is absent or nonfunctional (ie, DI), then free H2O can't be reabsorbed - urine will be? urine osmolality?

Back 22

Urine will be dilute. The urine osm will be <100 instead of >700-800 mosmol/kg. This indicates diabetes insipidus.

Front 23

To distinguish between central DI from nephrogenic Di, give ______. The results could show?

Back 23

ddAVP

- If urine osm rises = central DI
- If urine osm has little or no rise = nephrogenic DI

Front 24

If urine osm is 300-800 mosmol/kg (middle range) with hypernatremia, then the cause can be either _____ or ____.

Back 24

Partial DI (some ADH being released, but not enough) or Osmotic Diuresis

Front 25

How can partial DI and osmotic diuresis be differentiated in hypernatremia?

Back 25

By total solute excretion (urine osm x daily urine volume).

Elevated (>1000) suggests increased solute excretion from OSMOTIC DIURESIS (glucose, urea)

Front 26

Usually in hyponatremia, ________ is reduced.

Back 26

plasma osmolality

(b/c plama osm is mainly determined by sodium)

Front 27

In some cases of hyponatremia, the plasma osmolality may be normal or elevated - this is called?

Back 27

Pseudohyponatremia (falsely low - something is replacing a portion of the plasma and making sodium levels look low)

Front 28

What are the 3 main conditions that can cause pseudohyponatremia? What else?

Back 28

1) Hyperproteinemia
2) Hyperlipidemia
3) Hyperglycemia

(Also absorption/infusion of sucrose, maltose, glycine, or mannitol)

Front 29

If pseudohponatremia is due to hyperglycemia, what can be done?

Back 29

It can be corrected by adding 1.6 mEq/L sodium for EACH 100 mg/dL rise in glucose above 100.

Front 30

Example:
Sodium = 132 mEq/L
Glucose = 400 mg/dL

What's the corrected sodium?

Back 30

Glucose is 3 units above 100 mg/dL.

1.6 mEq/L x 3 = 4.8 mEq/L Na+ to add

Corrected Na+ = 132 + 4.8 = 136.8 mEq/L

Front 31

What is the normal response to hyponatremia with low plasma osmolality? What should the urine osmolality be?

Back 31

Suppression of ADH, causing more free water excretion to return plasma osm to normal. The urine osm should be <100. This means the ADH-Renal axis is intact.

Front 32

Hyponatremia: if urine osmolality is >100, there's an inability to excrete free H2O - what can this be accompanied by?

Back 32

1) Decreased effective circulating volume ("appropriate")

2) Normal ECF volume ("inappropriate")

Front 33

What can cause decreased ECF volume, hyponatremia and urine osmolality of >100?

Back 33

Heart failure; cirrhosis; renal insufficiency; nephrotic syndrome; diurectics, vomiting; other

It is "appropriate" that ADH is still being released.

Front 34

What can cause normal ECF volume, hyponatremia, and urine osmolality of >100?

Back 34

SIADH (Syndrome of Inappropriate Antidiuretic Hormone); hypothyroidism; adrenal insufficieny

It is "inappropriate" for ADH to still be released.

Front 35

If it's unclear whether a patient is hypovolemic or euvolemic, what might help?

Back 35

A urine sodium may help.

- Urine Na < 25 = Hypovolemic
- Urine Na > 25 = Euvolemic
- Urine Na 25 - 40 = unclear

Front 36

If a urine sodium is between 25 - 40 & it's unclear whether patient is hypovolemic or euvolemic, what can be done to clarify?

Back 36

- Give isotonic saline
- If hypovolemic, the fluid removes stimulus for ADH release, causing more dilute urine & normalization of serum sodium
- If SIADH, urine osm remains high while Na+ excretion is promoted by volume expansion

Front 37

Describe the characteristics of SIADH.

Back 37

1) Euvolemic hyponatremia
2) Low plasma osmolality
3) Inappropriately high urine osm (>100)
4) Urine Na > 40 mEq/L

Hint 37

4 important descriptors

Front 38

What is normal plasma potassium?

Back 38

3.5 - 5.0 mEq/L

Front 39

What is K+ secretion directly linked to?

Back 39

Directly linked to Na+ reabsorption

Front 40

What is the influence of K+ secretion?

Back 40

Aldosterone and natriuretic peptides

(may decrease K+ secretion in response to hypokalemia)

Front 41

Renal K+ handling is also linked to?

Back 41

Renal handling of H+ and Cl-

(this system is activated by hypokalemia, & stimulates production of K+/H+ - ATPase)

Front 42

Define hypokalemia and the normal response.

Back 42

Hypokalemia = plasma K+ = <3.5

Response is to lower K+ excretion to below 25-30 mEq per day OR 15 mEq/L

Front 43

What is the normal range for plasma sodium?

Back 43

136 - 144 mEq/L

Front 44

What is a normal spot urine?

Back 44

Greater than 25 mEq/L

(<25 indicates dehydration)

Front 45

What is the normal range for plasma potassium?

Back 45

3.5 - 5.0 mEq/L

Front 46

What is the normal range for plasma chloride?

Back 46

98 - 106 mEq/L

Front 47

What is the normal range for plasma bicarbonate?

Back 47

24 mEq/L

Front 48

What is the normal total plasma calcium?

Back 48

8.8 - 10.3 mg/dL

Front 49

What is the normal ionized calcium range?

Back 49

4.5 - 5.5 mg/dL

Front 50

What is normal serum phosphate?

Back 50

2.5 - 4.5 mg/dL

Front 51

What is normal serum magnesium?

Back 51

1.4 - 2.0 mg/dL

Front 52

What is the normal WBC count?

Back 52

4,400 to 11,000 cells/mm3

Front 53

What is normal hematocrit in males and females?

Back 53

Male: 46
Female: 40

Front 54

What is normal platelet count?

Back 54

150,000 to 450,000 cells/mm3

Front 55

What is normal hemoglobin amount in blood in males and females?

Back 55

Male: 15.7
Female: 13.8

Front 56

What is normal MCV (mean cell volume)?

Back 56

88 fL

Front 57

What is normal MCH (mean cell hemoglobin)?

Back 57

30.4 pg/RBC

Front 58

What is normal MCHC (mean cell hemoglobin concentration)?

Back 58

34.4 g/dL

Front 59

What is normal RDW (red blood cell distribution width)?

Back 59

13.1

(clinically, there is only normal or elevated RDW)

Front 60

What is normal INR (international normalized ratio)?

Back 60

0.8 - 1.2

Front 61

Which cells account for most of the white blood cells?

Back 61

Neutrophils and lymphocytes

Front 62

What is normal bleeding time?

Back 62

1 - 9 minutes

Front 63

A fractional excretion of sodium (FENa) of <1% indicates?

Back 63

Volume depletion

Front 64

What does sensitivity refer to? What equation represents sensitivity?

Back 64

Those who test positive for disease.

It equals TP / TP + FN

(ratio of all true positives over the total amount of those thought to have disease (true + and false + )

Front 65

What does specificity refer to? What equation represents specificity?

Back 65

Those who test negative for disease

It equals TN / TN + FP

(ratio of all true negatives over the sum of those thought to be without disease (true - and false - )

Front 66

What is positive predictive value?

Back 66

The probability that a patient with a positive test actually has the disease.

PPV = TP / TP + FP
`
(greater PPV - more meaningful likelihood ratio)

Front 67

What is negative predictive value?

Back 67

The probability that a patient with a negative test is truly free of the disease.

NPV = TN / TN + FN

Front 68

What is the positive likelihood ratio?

Back 68

The probability that a pt with disease will test positive by the probability that a pt without the disease will test positive

Higher LR = better test

Front 69

What is the negative likelihood ratio?

Back 69

The probability that a pt with disease will test negative by the probability that a pt without the disease will test negative

(lower negative LR = better test)

Front 70

A likelihood ratio of ____ means the test is meaningless.

Back 70

one

Front 71

The __________ _____ a likelihood is from 1, the more meaningful it is.

Back 71

further away

Front 72

Mean cell volume (MCV) can be elevated in ?

Back 72

- Alcoholism
- Liver Disease
- B12, folate deficiency
- Cold or Warm Agglutinins (RBC clumps)
- Reticulocytosis

Front 73

Mean cell volume (MCV) can be low in?

Back 73

- Iron deficiency
- Thalassemia
- Anemia of chronic disease

Front 74

Mean cell volume (MCV) can be normal in?

Back 74

Hemorrhage

Front 75

At what platelet count do you need for spontaneous bleeding?

Back 75

<10,000

Front 76

What is the gold standard for platelet counting?

Back 76

Peripheral smear