Developmental Hemostasis

Paul Monagle

Vera Ignjatovic

Leslie Roy Berry

Hemostasis is a complex homeostatic system that is critical to maintaining healthy life. Disturbances of the hemostatic system account for a large proportion of the noninfectious morbidity and mortality in westernized societies and are integral to many disease processes including cardiovascular disease, stroke, venous thrombosis, and even cancer. In some respects, nothing has changed since the mid-1800s when the German doctor, Rudolf Virchow, described the critical components of hemostasis as being the blood vessel wall, blood composition, and blood flow (Virchow triad). In considering the nonflow aspects of this equation, hemostasis can be considered as an interaction between the blood vessel wall, coagulation proteins within the plasma, and blood cellular components, predominantly platelets. Clearly over recent years, however, there has been an explosion in our understanding of the interactions within this system, and in particular, of the roles of individual plasma proteins. The hemostatic system interacts with other physiologic systems such as wound repair, inflammation, and angiogenesis in a complex and as yet incompletely understood manner.

Hemostasis is a dynamic, evolving process that is age dependent and begins in utero. The evolution of the hemostatic system continues throughout life, as evidenced by studies of the coagulation system in centenarians.¹ However, the changes are most marked during childhood and hence are of most clinical relevance during this time. Although evolving, the hemostatic system in healthy fetuses, infants, and children must be considered physiologic. The term “Developmental Hemostasis” was coined in the late 1980s by Dr. Maureen Andrew to describe this phenomenon. Dr. Andrew demonstrated in a single large cohort study of Canadian children that the concentrations of the majority of coagulation proteins, as measured by functional assays, changed significantly with age. The landmark papers, published in Blood in 1987, 1988, and 1992, not only changed the approach to research related to the coagulation system in children, but also the clinical interpretation of coagulation assays used by many hemostasis laboratories around the world since that time.², ³, ⁴

This chapter outlines our current understanding of developmental hemostasis, focusing on the plasma proteins. While there is evidence of age-related developmental changes in platelets⁵, ⁶, ⁷, ⁸, ⁹, ¹⁰ and the blood vessel wall,⁶, ⁷, ⁸, ⁹, ¹⁰, ¹¹ these changes are beyond the scope of this chapter. The implications of developmental hemostasis are discussed, in particular the clinical implications, the evidence that the age-related changes in the coagulation system influence the age-related epidemiology of thromboembolic disease, and the potential implications of developmental hemostasis for integrated physiologic systems. The impact of development hemostasis on the pharmacology and effectiveness of anticoagulant drugs are discussed in Chapter 121. There remain many gaps in our knowledge, and much work is required in this area. An understanding of developmental hemostasis in the broadest sense optimizes the prevention, diagnosis, and treatment of hemostatic problems during childhood and undoubtedly provides new insights into the pathophysiology of hemorrhagic and thrombotic complications for all ages.

THE HEMOSTATIC SYSTEM

The fundamental principle underlying developmental hemostasis is that the functional levels of coagulation proteins change in a predictable way with age.¹² While the absolute values of these changes are reagent and analyzer dependent, the trends in changes observed are consistent across a number of studies.¹³ These changes in functional protein levels are reflected in the results of global tests of coagulation such as the activated partial thromboplastin time (APTT). Other global measures of hemostasis may be more or less sensitive to age-related changes in hemostatic proteins. For example, there is little difference in normal thromboelastography (TEG) with age.¹⁴ Studies in this field have predominantly involved functional assays of the coagulation proteins due to the fact that these assays are commonly used in clinical practice. In fact, differences in immunologic levels of the coagulation proteins have not been reported to date. Table 119.1 lists major studies that have described age-related changes in coagulation proteins and routine coagulation assays. Tables 119.2, 119.3, 119.4, 119.5, 119.6, 119.7, 119.8 list values for these parameters as reported in a more recent publication.

Early evidence suggests that these age-related changes in protein concentration are not isolated to the coagulation system, but are in fact evident across multiple protein systems within the plasma proteome. Variation in the human plasma proteome with age has been examined using plasma samples collected from healthy neonates (day 1 and day 3), children (<1 year, 1 to 5, 6 to 10, and 11 to 16 years), and adults. The study reported significant changes in number and abundance of up to 100 proteins across various age groups tested.²⁶ FIGURE 119.1 shows a two-dimensional (2-D) DIGE gel image demonstrating differences in plasma protein abundance between a day 1 neonate and an adult. Table 119.9 lists the plasma proteins that were shown in this initial study to significantly change in abundance with age. Further work is required to identify the many more proteins that likely change consistently with age. The implications of these age-related changes are yet to be understood.

The possibilities for how plasma levels of coagulation proteins are different in children compared to adults include regulation at the gene level, posttranslational modifications (PTMs) that affect protein function, delivery or release of proteins, as well as differences in protein clearance. A recent study

demonstrated that even with a transplanted adult liver in situ, children maintain plasma levels of certain coagulation proteins at their expected age-specific levels.²⁷ Thus the liver, despite being the site of production for most of the coagulation proteins, is not the regulator of plasma levels. The authors hypothesized hormonal control, vascular endothelial control via an as yet unidentified mechanism, or control via variable clearance. However, whatever the mechanism, the vascular endothelium seems the most likely candidate as the primary regulator.²⁸ The endothelium is intimately involved with the function of the coagulation proteins.²⁹ Vascular endothelial dysfunction, as observed in disseminated intravascular coagulation, is usually measured by the degree of disturbance in coagulation proteins, even though it is not a primary disorder of coagulation.³⁰

Table 119.1 Studies reporting age-related differences in coagulation assays or proteins during childhood

Author	Year	Assays/Proteins Reported	Age Groups	N
Perlman¹⁵	1975	PT, TT, APTT, fibrinogen, FDP, platelet count, hematocrit, FV, FVIII, plasminogen, hemoglobin	Healthy infants Small-for-dates infants Postmature infants	N = 35 N = 26 N = 30
Beverley et al.¹⁶	1984	APTT, FII-VII-X, fibrinogen, α₂-antiplasmin, platelet count, MPV, megathrombocyte index, plasminogen	Cord blood Newborns (48 h)	N = 80
Andrew et al.³	1987	PT, APTT, TCT, fibrinogen, FII, FV, FVII, FVIII, vWF, FIX, FX, FXI, FXII, PK, HMW-K, FXIIIa, FXIIIb, plasminogen, AT, α₂-M, α₂-AP, C₁E-INH, α₁-AT, HCII, protein C, protein S	Day 1 newborn Day 5 newborn Day 30 newborn Day 90 newborn Day 180 newborn Adult	28-75 samples per age group
Andrew et al.²	1988	PT, APTT, TCT, fibrinogen, FII, FV, FVII, FVIII, vWF, FIX, FX, FXI, FXII, PK, HMW-K, FXIIIa, FXIIIb, plasminogen, AT, α₂-M, α₂-AP, C₁E-INH, α₁-AT, HCII, protein C, protein S	Premature newborns (30-36 wk gestation) Day 1 Day 5 Day 30 Day 90 Day 180	23-67 samples per age group
Andrew et al.⁴	1992	PT/INR, APTT, bleeding time, fibrinogen, FII, FV, FVII, FVIII, vWF, FIX, FX, FXI, FXII, PK, HMW-K, FXIIIa, FXIIIs, plasminogen, TPA, PAI, AT, α₂-M, α₂-AP, C₁E-INH, α₁-AT, HCII, protein C, protein S (total and free)	1-5 y 6-10 y 11-16 y Adults	20-50 samples per age group
Reverdiau-Moalic et al.¹⁷	1996	PT/INR, APTT, TCT, FI, FII, FVII, FVII, FIX, FX, FV, FVIII, FXI, FXII, PK, HMWK, AT, HCII, TFPI, protein C (Ag, Act), protein S (free and total), C4b-BP	Fetuses 19-23 wk gestation 24-29 wk gestation 30-38 wk gestation Newborns (immediately after delivery) Adults	N = 20 N = 22 N = 22 N = 60 N = 40
Carcao et al.¹⁸	1998	PFA100 Hb Platelet count	Neonates Children Adults	N = 17 N = 57 N = 31
Salonvaara et al.¹⁹	2003	FII, FV, FVII, FX, APTT, PT/INR, platelet count	Premature infants 24-27 wk 28-20 wk 31-33 wk 34-36 wk	N = 21 N = 25 N = 34 N = 45
Flanders et al.²⁰	2004	PT, APTT, FVIII, FIX, FXI, AT, RCF, vWF, protein C, protein S	7-9 y 10-11 y 12-13 y 14-15 y 16-17 y Adults	124 per age group
Monagle et al.¹³	2006	APTT (four reagents), PT/INR, fibrinogen, TCT, FII, FV, FVII, FVIII, FIX, FX, FXI, FXII, AT, protein C, protein S, D-dimers, TFPI (free and total), endogenous thrombin potential	Day 1 Day 3 <1 y 1-5 y 6-10 y 11-16 y Adults	Minimum 20 samples per age group
Chan et al.¹⁴	2007	TEG [R. K. a, MA, LY30]	<1 years 1-5 y 6-10 y 11-16 y Adults	N = 24 N = 24 N = 26 N = 26 N = 25
Sosothikul et al.²¹	2007	PT, APTT, fibrinogen, TAT, PC:Ac, TF, FVIIa, sTM, vWF (Ag and RCo), D-dimer, tPA, PAI-1, TAFI	1-5 y 6-10 y 11-18 y Adults	N = 19 N = 26 N = 25 N = 26
Mitsiakos et al.²²	2009	INR, PT, APTT, fibrinogen, FII, FV, FVII, FVIII, FIX, FX, FXI, FXII, AT, protein C, protein S, APCr, tPA, PAI-1, vWF	Small-for-growth newborns Appropriate for growth newborns	N = 90 N = 98
Newall et al.²³	2008	PF4 and vitronectin	<1 y 1-5 y 6-10 y 11-16 y Adults	15 per age group
Ries et al.²⁴	1997	TAT, F1+2, PAP, D-dimer	1-6 y 7-12 y 13-18 y Adults	20 per age group
Boos et al.²⁵	1989	PIVKA II, FVII, FII, FII:Ag	Day 1, 2, 3 neonates	N = 57 total

To date, efforts to understand developmental differences in the hemostatic system have mostly focused on quantitative differences in coagulation proteins based on functional assays.³, ⁴, ¹² However, coagulation proteins have complex tertiary structures, which in general bestow multiple functions.³¹, ³² PTMs affecting the structure of hemostatic proteins are known to occur and likely have significant impact on the function of these proteins.³¹, ³² As an example, fibrinogen has previously been demonstrated to exist in a “fetal” form, in cord blood of term infants.³² This “fetal” form of fibrinogen has increased sialic acid content compared to adult fibrinogen, a direct result of PTM. The phosphorus content of fetal fibrinogen is increased up to fourfold compared to the adult form of this protein.³³, ³⁴ In addition, thrombin clotting times are prolonged in newborns, suggesting differences in polymerization of fibrin from “fetal” fibrinogen,³⁵ an observation that has led to claims that fibrinogen in infants is “dysfunctional.”³⁶ The importance of differences in sialic acid content of fibrinogen is in the fact that sialic residues of fibrinogen directly bind Ca²⁺,³⁷ leading to a decrease in the intermolecular repulsion between fibrinogen chains and thereby facilitating fibrin polymerization.³⁷

A recent study investigating differences in fibrinogen purified from neonates and children to that from adults determined that the molecular weight of the Aα fibrinogen chain

was consistently higher by up to 1,500 Da in neonates and children compared to adults.³⁸ This trend toward a higher molecular weight of fibrinogen chains in younger age groups was also consistent for the Bβ and γ chains with differences of up to 400 and 500 Da, respectively. These differences in fibrinogen chains could represent multiple additional sialic acid or residues associated with increased glycan branching³⁹ in the neonatal and pediatric fibrinogen compared to the adult form of this protein. The same study also demonstrated significant differences in the chromatogram profile (area under the peak and peak height) in neonates and children compared to adults, suggesting differences in the interaction of the fibrinogen molecule from each age group with the chromatography column used, which also implies structural differences for fibrinogen in these age groups.³⁸

Table 119.2 APTT reference values for neonates and children using four different reagents compared to APTT results from Andrew et al.³, ⁴

	Age
APTT Results (s)	Day 1	Day 3	1 Month-1 Year	1-5 Years	6-10 Years	11-16 Years	Adults
PTT-A	38.7^a (34.3-44.8) N = 21 (10F/11M)	36.3^a (29.5-42.2) N = 25 (13F/12M)	39.3^a (35.1-46.3) N = 35 (3F/30M)	37.7^a (33.6-43.8) N = 56 (26F/30M)	37.3^a (31.8-43.7) N = 71 (27F/44M)	39.5^a (33.9-46.1) N = 54 (12F/42M)	33.2 (28.6-38.2) N = 42
CK PREST	Not available	Not available	34.4^a (31.1-36.6) N = 20 (3F/17M)	32.3^a (29.8-35.0) N = 22 (11F/11M)	32.9^a (30.8-34.8) N = 22 (12F/10M)	34.1^a (29.4-40.4) N = 39 (8F/31M)	29.1 (25.7-31.5) N = 40
Actin FSL	Not available	Not available	37.4^a (33.4-41.4) N = 20 (3F/17M)	36.7^a (31.8-42.8) N = 20 (10F/10M)	35.4^a (30.1-40.4) N = 21 (12F/9M)	38.1^a (32.2-42.2) N = 39 (9F/30M)	30.8 (27.1-34.3) N = 40
Platelin L	Not available	Not available	36.5^a (33.6-40.4) N = 20 (3F/17M)	37.3^a (32.5-43.8) N = 21 (11F/10M)	35^a (31.0-39.3) N = 22 (12F/10M)	39.4^a (32.6-49.2) N = 35 (7F/28M)	31.3 (27.2-35.4) N = 38
Andrew et al.³ , ⁴	42.9^b (31.3-54.5)	42.6^b (25.4-59.8)	35.5 (28.1-42.9)	30 (24-36)	31 (26-36)	32 (26-37)	33 (27-40)
For each reagent, the first row shows the mean and boundaries including 95% of the population. The second row shows the number of individual samples and the ratio of males to females for each group.
^aValues that are significantly different from adult values (P < 0.05). ^bValues that are significantly different from adult values for data from Andrew et al.³ , ⁴
M, males; F, females.
NOTE: Andrew et al.³ , ⁴ results for day 3 are actually day 5 results.
Reproduced from Monagle P, Barnes C, Ignjatovic V, et al. Developmental haemostasis. Impact for clinical haemostasis laboratories. Thromb Haemost 2006;95(2):362-372, with permission.

Table 119.3 TCT, PT, INR, and fibrinogen reference values for neonates and children compared to results from Andrew et al.³, ⁴

	Age
Coagulation Tests	Day 1	Day 3	1 Month-1 Year	1-5 Years	6-10 Years	11-16 Years	Adults
Thrombin clotting time (TCT) (s)	Not available	Not available	17.1^a (16.3-17.6) N = 20 (10F/10M)	17.5^a (16.5-18.2) N = 21 (11F/10M)	17.1 (16.1-18.5) N = 21 (11F/10M)	16.9 (16.2-17.6) N = 22 (11F/11M)	16.6 (16.2-17.2) N = 20
TCT Andrew et al.³ , ⁴	23.5 (19.0-28.3)	23.1 (18.0-29.2)	24.3 (19.4-29.2)	Not available	Not available	Not available	Not available
Prothrombin time (PT) (s)	15.6^a (14.4-16.4) N = 21 (10F/11M)	14.9^a (13.5-16.4) N = 25 (13F/12M)	13.1 (11.5-15.3) N = 35 (8F/27M)	13.3^a (12.1-14.5) N = 43 (23F/20M)	13.4^a (11.7-15.1) N = 53 (22F/31M)	13.8^a (12.7-16.1) N = 23 (7F/16M)	13.0 (11.5-14.5) N = 51
PT Andrew et al.³ , ⁴	13 (11.6-14.43)	12.4 (10.5-13.86)	12.3 (10.7-13.9)	11 (10.6-11.4)	11.1 (10.1-12.1)	11.2 (10.2-12.0)	12.0 (11.0-14.0)
International Normalised Ratio (INR)	1.26^a (1.15-1.35) N = 21 (10F/11M)	1.20^a (1.05-1.35) N = 25 (13F/12M)	1.00 (0.86-1.22) N = 35 (8F/27M)	1.03^a (0.92-1.14) N = 43 (23F/20M)	1.04^a (0.87-1.20) N = 53 (22F/31M)	1.08^a (0.97-1.30) N = 23 (7F/16M)	1.00 (0.80-1.20) N = 51 (43F/8M)
INR Andrew et al.³ , ⁴	1^b (0.53-1.62)	0.91^b (0.53-1.48)	0.88^b (0.61-1.17)	1 (0.96-1.04)	1.01 (0.91-1.11)	1.02 (0.93-1.10)	1.10 (1.0-1.3)
Fibrinogen (g/L)	2.80 (1.92-3.74) N = 22 (10F/12M)	3.30 (2.83-4.01) N = 21 (10F/11M)	2.42^a (0.82-3.83) N = 34 (7F/27M)	2.82^a (1.62-4.01) N = 43 (23F/2OM)	3.04 (1.99-4.09) N = 52 (22F/30M)	3.15 (2.12-4.33) N = 21 (7F/14M)	3.1 (1.9-4.3) N = 55 (47F/8M)
Fibrinogen Andrew et al.³ , ⁴	2.83 (2.25-3.41)	3.12 (2.37-3.87)	2.51 (1.5-3.87)	2.76 (1.70-4.05)	2.75 (1.57-4.0)	3 (1.54-4.48)	2.78 (1.56-4.0)
^aValues that are significantly different from adult values (P < 0.05). ^bValues that are significantly different from adult values for data from Andrew et al.³ , ⁴
M, males; F, females.
NOTE: Andrew et al.³ , ⁴ results for day 3 are actually day 5 results.
Reproduced from Monagle P, Barnes C, Ignjatovic V, et al. Developmental haemostasis. Impact for clinical haemostasis laboratories. Thromb Haemost 2006;95(2):362-372, with permission.

Table 119.4 Coagulation factor reference values for neonates and children compared to results from Andrew et al.³, ⁴

	Age
Coagulation Factors (%)	Day 1	Day 3	1 Month-1 Year	1-5 Years	6-10 Years	11-16 Years	Adults
II	54^a (41-69) N = 23 (13F/10M)	62^a (50-73) N = 22 (11F/11M)	90^a (62-103) N = 22 (7F/15M)	89^a (70-109) N = 67 (26F/41M)	89^a (67-110) N = 64 (23F/41M)	90^a (61-107) N = 23 (6F/17M)	110 (78-138) N = 44
II Andrew et al.^3,4	48^b (37-59)	63^b (48-78)	88^b (60-116)	94^b (71-116)	88 (67-107)	83^b (61-104)	108 (70-146)
V	81^a (64-103) N = 22 (13F/9M)	122 (92-154) N = 22 (11F/11M)	113 (94-141) N = 20 (6F/14M)	97^a (67-127) N = 75 (26F/41M)	99^a (56-141) N = 64 (23F/41M)	89^a (67-141) N = 20 (5F/15M)	118 (78-152) N = 44
V Andrew et al.^3,4	72^b (54-90)	95^b (70-120)	91^b (55-127)	103 (79-127)	90^b (63-116)	77^b (55-99)	106 (62-150)
VII	70^a (52-88) N = 22 (12F/10M)	86^a (67-107) N = 22 (11F/11M)	128 (83-160) N = 20 (6F/14M)	111^a (72-150) N = 66 (25F/41M)	113^a (70-156) N = 64 (23F/41M)	118 (69-200) N = 22 (6F/16M)	129 (61-199) N = 44
VII Andrew et al.^3,4	66^b (47-85)	89^b (62-116)	87^b (47-127)	82^b (55-116)	85 (52-120)	83^b (58-115)	105 (67-143)
VIII	182 (105-329) N = 20 (9F/11M)	159 (83-274) N = 25 (12F/13M)	94^a (54-145) N = 21 (6F/15M)	110^a (36-185) N = 45 (26F/19M)	117^a (52-182) N = 52 (20F/32M)	120^a (59-200) N = 24 (6F/18M)	160 (52-290) N = 44
VIII Andrew et al.^3,4	100 (61-139)	88 (55-121)	73^b (50-109)	90 (59-142)	95 (58-132)	92 (53-131)	99 (50-149)
IX	48^a (35-56) N = 24 (11F/13M)	72^a (44-97) N = 23 (11F/12M)	71^a (43-121) N = 21 (5F/16M)	85^a (44-127) N = 44 (25F/19M)	96^a (48-145) N = 51 (19F/32M)	111^a (64-216) N = 25 (6F/19M)	130 (59-254) N = 44
IX Andrew et al.^3,4	53^b (34-72)	53^b (34-72)	86^b (36-136)	73^b (47-104)	75^b (63-89)	82^b (59-122)	109 (55-163)
X	55^a (46-67) N = 22 (12F/10M)	60^a (46-75) N = 22 (11F/11M)	95^a (77-122) N = 21 (6F/15M)	98^a (72-125) N = 66 (25F/41M)	97^a (68-125) N = 49 (20F/29M)	91^a (53-122) N = 24 (7F/17M)	124 (96-171) N = 44
X Andrew et al.^3,4	40^b (26-54)	49^b (34-64)	78^b (38-118)	88^b (58-116)	75^b (55-101)	79^b (50-117)	106 (70-152)
XI	30^a (7-41) N = 20 (10F/10M)	57^a (24-79) N = 22 (11F/11M)	89^a (62-125) N = 22 (6F/16M)	113 (65-162) N = 41 (24F/17M)	113 (65-162) N = 50 (18F/32M)	111 (65-139) N = 24 (5F/19M)	112 (67-196) N = 44
XI Andrew et al.^3,4	38^b (24-52)	55^b (39-71)	86^b (49-134)	97 (56-150)	86 (52-120)	74 (50-97)	97 (67-127)
XII	58^a (43-80) N = 20 (9F/11M)	53^a (14-80) N = 21 (11F/10M)	79^a (20-135) N = 21 (7F/14M)	85^a (36-135) N = 39 (20F/19M)	81^a (26-137) N = 45 (17F/28M)	75^a (14-117) N = 22 (7F/15M)	115 (35-207) N = 44
XII Andrew et al.^3,4	53^b (33-73)	47^b (29-65)	77^b (39-115)	93 (64-129)	92 (60-140)	81^b (34-137)	108 (52-164)
^aValues that are significantly different from adult values (P < 0.05). ^bValues that are significantly different from adult values for data from Andrew et al.³ , ⁴
M, males; F, females.
NOTE: Andrew et al.³ , ⁴ results for day 3 are actually day 5 results.
Reproduced from Monagle P, Barnes C, Ignjatovic V, et al. Developmental haemostasis. Impact for clinical haemostasis laboratories. Thromb Haemost 2006;95(2):362-372, with permission.